MadModder
Gallery, Projects and General => Project Logs => Topic started by: NickG on November 20, 2010, 12:21:28 PM
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I've been to the doctors and diagnosed with :proj: again! :doh:
This is annoying as I now have 3 projects on the go - not counting the bigger ones!
The other annoying thing is that my projects always start off as a quickie but don't end up that way - this time it was Jan Ridder's fault again! He recently posted his Micro Stirling Engine on his website - I had to see it so asked for the plans, which he was very kind to send to me. The problem is, I just don't like making stuff from other peoples plans blindly! It never seems to suit my materials or processes so I have to change things - but I probably go too far.
This time I've tried to combine the best ideas from Jan's and another engine I found on youtube - see below:
http://heetgasmodelbouw.ridders.nu/Webpaginas/pagina_stirling_1_euro_10/frameset.htm
Mine is going to end up a little larger than these two mainly to make things a bit easier for myself and what I have to hand, it should also give it a slightly better chance of running.
I have done the CAD model which took a bit of working out but have not yet done the 2D drawings. Please see attachment for the 3D model. I did calculations to ensure the ratio of swept volumes between displacer piston and power piston are almost the same - this is quite important as it largely governs the temperature difference the engine can run on, of course there are a lot of other factors but I think this engine should work.
Need to crack on and produce the drawings over the next few days and get cutting some metal - otherwise I'll have projects coming out of my ears!
Nick
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this will be very interesting to watch :)
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Hi Nick, seems weīre both making Stirlings. Mine will be bigger, yours is really small. I d/loaded your CAD model, the yellow parts are obviously brass, flywheel seems to be aluminium. How about the pistons? Graphite power, I guess, but whatīs the displacer made of? And the displacer cylinder? Ball bearings, I assume? In the video, the flywheel seems to be acrylic(?).
I might try an LTD Stirling sometime soon, but not quite this small :) In HMEM, thereīs an ongoing build of an alpha-type Stirling that refuses to run. I must be daft, but I canīt see why or how it would run... :scratch:
Although I know that (some) alpha Stirlings DO run...
Looking forward to many pictures, Iīm going to watch this both eyes wide open!
:wave:
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I like that Nick :thumbup:
I may have a go at one when you've got the drawing completed.
Stew
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Looking forward to this project Nick. :wave:
Good luck! :thumbup:
David D
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Thanks for the interest guys.
Is still have a couple of issues to sort out with the design. The crankshaft on mine is turned from a piece of solid brass - it might be a bit heavy but I can balance the assembly later by adding mass to 1 side of the flywheel. Hopefully, as my cc is larger, the engine will have enough about it to turn it over. It shouldn't be difficult to machine but I'll have to do things in the right order as it will not have much structural integrity once I start cutting the journals. The other problem doing it from solid is how do you get the big ends on?! Jan's plans suggest putting small slit at the end of the con rod into the big end hole, the rod is that thin you can simply bend it, push it over the crank journal and it'll spring back - I don't really like the sound of that so was racking my brains to think of something else - I can't think of something simple so it seems Jan's idea is a good one.
You're right about all the materials Olli. The displacer is supposed to be balsa wood (I know, the colour is wrong!) but I might have to see what else I have that's suitable - might have some balsa somewhere. I think the flywheel in the vid looks like acrylic. I've found some plastic for my displacer cylinder - top off sun cream, might work, might not, if not I'll have to do what Chris suggested and go around tesco's with my digi vernier :lol:
Ade kindly sent me the graphite for the piston so I'll be attempting that.
I'm not sure what an Alpha type engine is Olli - I was up to speed on this sort of stuff but have forgotten, would have to read up again! Is it the type where the displacer makes a seal too rather than allowing the air around it? I think you need a lot of heat for them and they usually have a low ratio of swept volumes to keep everything as efficient as possible? Or am I thinking of something else?
I'll have to get on with the drawings later but I won't post them until I know it works!
Nick
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Hi Nick, interesting build, funny you should only have three projects going, are you ever going to be a serious modeler? :poke: A beta Stirling is one where the power piston runs in the same cylinder as the displacer, and is probably the most efficient, it certainly is in large scale. An alpha type is one with a separate displacer cylinder and power cylinder, with the two connected, and easiest to make LTDs since they tend to have large diameter displacer cylinders, and short strokes, with long stroke, hence high torque power pistons, to make them work well at low differentials. I only know this because I'm starting one of each at the moment, and am still gathering materials. :hammer: mad jack
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Hi Madjack,
:lol: I said I wasn't including the larger projects, mainly because it just depresses me - can I never finish anything?! I might as well mention them now though, they include the refurbishment of a 3 1/2" gauge locomotive (same as Stew's as it happens), refurbishment of a 4 1/2" scale wallis & stevens simplicity Steam Roller, building of a 5" gauge sweet pea locomotive and not a model but the restoration of a 1989 Ford Escort RS Turbo - all work in progress but haven't done much with any of them for a long time. Every time I look at any of them more seriously, I find something that makes them become an even larger project :doh:
Thanks for explaining the different stirling cycle engines. I have made 1 stirling so far to my own design, it was an alpha type engine with the cylinders at 90 degrees to each other enabling use of the same crank.
I remember coming across another type of engine though, I can't remember the designation, still two cylinders but they both have air tight pistons - can't quite remember how they work, willhave to have a look. THink there is a regenerator in the middle and somehow both pistons provide a power stroke?
Nick
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Wow that is a tiny Sterling. Best of luck on this one Nick. I know I will be watching.
Eric
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Hi Nick, there is a "Ringbom" Stirling, which has a piston which moves just the displacer, and has a separate power piston which moves according to the pressure differential, and there is a "resonance" or "acoustic resonance" type where it has a single piston, a heat chamber with good insulation from the cylinder and piston with the cylinder well cooled, and relies on a "resonating pressure pulse" established by the heat raising the pressure, and the power piston setting up a pulse, which will settle into driving the piston at the resonant frequency of the pressure wave in the closed cycle, as it alternates between pressure and temperature change, as per the first law of thermodynamics, I believe, which says in a closed system, the pressure of a gas will be directly proportional to the relative temperature, so the piston changing the volume allows the temperature to turn into pressure when the volume is reduced, and pushes the piston out, which increases the volume, allowing the air to cool, with the excess heat carried off by the mass of the cylinder, piston and the rest of the "cool" end of the engine, which takes it below its original pressure, so it expands faster when all the air is pushed into the hot end, and raising the pressure again. The phase shift takes place in the transfer of the heat to pressure, and the change of pressure with the "loss" of heat when the piston has been moved, and has lowered the pressure by increasing the volume, and at the same time, losing some of the energy of the heat also through transfer, causing the resonant effect which acts in place of a displacer. This engine seems to work by applying the same principle of a "hydraulic ram", pumping system which uses the inertia of running water to establish a resonance, and pump by just changing the pressure in a closed chamber with valves to bleed off excess water, and keep a resonating pressure change continuing and the inertia of the water actually doing the pumping. There is a video of this form of single piston Stirling among the videos available at the beginning of this post. It has taken a lot of mind bending to get around this idea and make it make sense, but having seen it work, it must make sense. :loco: mad jack
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Count me in on the peanut gallery crowd Nick :beer:
Have to get around to an LTD myself at some point... A "normal" sterling as well!
Kind regards, Arnold
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Thanks for the info Madjack, I've often been fascinated by the acoustic resonance and thermal lag type engines but have never made the effort to understand how they work! I will have to read your post a few times to get it to sink in. The type of engine I've seen isn't that or a ringbom though, it's more like the following link, except I didn't realise it was 'Rider' engine: http://www.stirlingengines.org.uk/work/cyc1.html (http://www.stirlingengines.org.uk/work/cyc1.html)
I think we're all getting confused with alpha and beta types - alpha is the sort I am talking about in link above, according to Wikipedia http://en.wikipedia.org/wiki/Stirling_engine (http://en.wikipedia.org/wiki/Stirling_engine) (and that was the way I understood it). The beta, as you rightly said has the loose fitting displacer which displaces air from a hot end to the cold end and the power and displacement pistons are in the same cylinder. The gamma is the one with a loose fitting displacer but there are separate power and displacement cylinders which are connected, so that is the sort I have made before and is what this LTD will be.
Nick
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Good grief!!!! That thing is small. Don't sneeze or you'll never find it. :D :D :D
You people that can do this small stuff have my greatest admiration. :bow: :bow:
Nice going Nick.
I have enough trouble with the size of Elmers engines.
Ron
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Thanks Eric, Arnold and Ron - but I haven't made an LTD myself yet, let alone this small! So the jury is out on whether I can do this small stuff or not yet!!!
If it doesn't work it'll get a metal displacer & cylinder and a blow torch underneath it! :lol:
Nick
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I've got to say, Nick, you've definitely got the right attitude :poke: I like that, put a metal displacer in it, and fire up a torch!! :lol: Sorry I forgot about the "big" projects you mentioned, I tend to forget about them because I have so many of my own sitting in the middle of repair, dis-repair, and mere contemplation. When I've got pictures of the different types, and their names under them, I can always tell what kind is which one, other than that, I'm easily confused once you get past the common ones, the alpha type, with the separate displacer cylinder and power cylinder, with the connecting hole, tube or line, and the beta, with both in one cylinder. I spent about an hour watching some of the fifteen or more examples in the link you attached to the beginning of this log, and have seen both the Ringbom type, and the accoustic resonance type running, as well as a whole set of ones I've heard of but never seen. It's quite a link to some very fine, and I mean fine, engineering. I think you'll get this one down just fine. :thumbup: :bugeye: mad jack
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Madjack,
I'm glad it's not just me, I knew it wasn't though - there must be so many unfinished projects out there, I bet some just an inch from completion of amazing models. But lots, like yours and mine in the middle of repair, dis-repair and occasional contemplation!
That's the problem with youtube - you click on something and then realise there are many others in the frame on the right, then when watching one of those, it brings up another 15! I love the Ringbom type engines, they are fascinating to watch! Last night was wasted on youtube instead of working on the drawings :poke:
I hope it goes to plan, am quite looking forward to it. I was planning to make two but I think I'll just go for one, otherwise I'll get bored and it'll be another part finished project!
Nick
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On the subject of small Stirlings, here's a nano version:
Andy
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:jaw:
That's impressive, watch maker?!
Nick
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That's impressive, watch maker?!
Nick
I don't know about that, but I believe he is very severely disabled. Goes to show that rather than giving up, you should just get on, do what you enjoy, and impress everyone with the results.
Andy
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Wow! And the reason I don't get things done is mainly laziness - puts things into perspective.
I did actually make some progress last night - I 2D drawings for 5 of the parts, but have another 11 to go. The good thing is, many of them aren't complicated - I'll probably hopefully get another few done tonight then the remainder on thurs night ready to start machining on the weekend!
Nick
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Got all the drawings done for the Tiny Stirling now and was planning to start machining over the weekend but as always, life gets in the way. Saturday I started painting the downstairs loo, Sunday the car broke down and won't start and today on the way to work the other car broke down and went into limp mode - nearly killing me, again! Only had it since August, was in the garage last week supposedly getting repaired for something that wasn't covered by the 3 month warranty - Ģ250 later then today, of all days, it cuts out when pulling onto motorway. In my experience all I can say is, don't buy a Citroen and don't buy from Evans Halshaw.
A very pissed off Nick! :bang:
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Thats a real bummer Nick luckily you weren't hurt.
Stew
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Ohh, Nick!.
Very sorry to hear that.....
It's amazing how life gets in the way of the best laid plans. :bang:
Hope you're soon sorted, and back to what passes as "normal"..... :thumbup:
David D
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thats bad luck mate hopr you get it sorted soon and back to normality
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Cheers guys, sorry, bit :offtopic: but I started ripping bits off the little Clio today to try and find out what's wrong. I was thinking it could be the crank angle sensor so have taken that off and ordered a new one, but while I was on I thought I'd whip the spark plugs out and do a compression test, as it sounded like there was no compression when turning the engine over - with my heath robinson compression tester (a grandad special!) there was zilch on any cylinder - will have to borrow a proper one to confirm it though. Not quite sure what it could be - cam belt could have slipped round? but would expect to see something on the gauge - valves stuck open possibly? - will have to get the rocker covers off to have a look at that. Anyway, will leave it there as this could be a whole new topic but you get the picture!
As for the other car (citroen) it's just too complicated for its own good, am incredibly annoyed, they are charging me Ģ85 to get a recovery truck to pick it up to "have a look at it" as far as I'm concerned it aint coming back, going to fight for my money back (or most of it) and try something else :doh:
As Stew said, no actual harm done though and I've finished painting the toilet so :) :ddb:
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Well Nick, that's what you get for posting a u-tube of tiny stirlings on your thread :poke: I spent almost an hour yesterday just looking at all the different tiny engines and wondering why I am planning on getting rid of any scrap at all. With all your cylinders showing no compression you either have a problem with the gauge and or its connection with the cylinders, which should be audible when cranking over, or you probably have a blown head gasket, which, with all cylinders affected, should also be audible when cranking. Unless you've got a very new vehicle which has valve controls I've never seen, even a timing belt or chain would leave at least one cylinder with the valves closed, and thus get compression. Kind of wish you were in my neighborhood, at least I could confirm your diagnosis. Hope things work out better for you, and know the level of inspiration you have raised with that tiny stirling, and the not quite as tiny flame sucker, which is absolutely stupendous. I'm also very taken with the tiny stirling set on the oak thumbnail, which runs so well and looks so perfect in all its glory, even when not running. :bugeye: :jaw: It might be time to work on a stirling powered vehicle, for reliability. :lol: mad jack
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Madjack,
you make a good point there about scrap! Until I made my flame gulper, I'd only ever used scrap bits of metal to make my engines. For the flame gulper though I was fed up of hunting around for bits and I knew I didn't have any cast iron so just took the opportunity to buy all the bits I needed whilst there. It was a bit of a revelation for me as I found rather than struggling on, all the material I bought machined beautifully! So horses for courses I guess. For the tiny stirling I will be using scrap again!
The engine on the Renault Clio is the 2.0 16v 172bhp - it has variable valve timing which I'm not that familiar with, apparently it could be something to do with that vvt pulley. I'm going to borrow another compression tester but I fear the worst, I put my hand over one of the spark plug holes and cranked - there was nothing! I'm at a loss trying to explain what's happened at the moment. I don't think it's head gasket as there is literally no compression and there is no oil in the water or vice versa. As you say, it should be audible when cranking but again, nothing! I'm with you on the cam belt - at least one of the cylinders would have both valves closed at some point and hence get compression. The only explanation I can come up with is that the at least 1 valve on each cylinder has stuck open - possibly being bent but then you would have thought I'd hear something metallic. I won't be able to confirm this until I get at least the rocker cover off though. Will see what the proper compression tester reveals and go from there!
:lol: I actually hate cars at the moment!
Nick
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Hi
in your first post you stated :
'I did calculations to ensure the ratio of swept volumes between displacer piston and power piston are almost the same - this is quite important as it largely governs the temperature difference the engine can run on, of course there are a lot of other factors but I think this engine should work'
If my understanding is right, this will result in a non running engine (its quite possible that I am incorrect as I have only recently started researching these). So please don't take offence.
These engines work on the expansion of air caused by increase of temperature. If the volume is fixed that's about 1 psi for every 5C. To return to normal atmospheric pressure the air will expand 1 / 273rd of its volume, so for 5C that would be around 2%.
For a coffee cup or LTD a reasonable differential would be 30C, with an expansion of 11% to normal atmospheric pressure. This would mean that the displacer volume / power piston ratio should be 89 - 11 or around 8 to 1.
If the displacer volume is larger, heat will be lost without doing work (no big deal), however if the ratio is the smaller then the energy produced will be lost as the piston works against the atmospheric pressure, overexpanding the gas.
As I said earlier, I am still coming to an understanding of these engines so feel free to tell me where I am wrong, I certainly will not be offended.
Best Regards
picclock
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These engines work on the expansion of air caused by increase of temperature. If the volume is fixed that's about 1 psi for every 5C. To return to normal atmospheric pressure the air will expand 1 / 273rd of its volume, so for 5C that would be around 2%.
For a coffee cup or LTD a reasonable differential would be 30C, with an expansion of 11% to normal atmospheric pressure. This would mean that the displacer volume / power piston ratio should be 89 - 11 or around 8 to 1.
Interesting stuff :D
Anyone know if using a scotch yoke on the displacer would help? My thinking here is that the yoke could provide additional dwell at the top/bottom centre of the displacer movement.
Bill
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Hi Bill
Thats what my post in the design section, vertical shaft LTD was about.
Its not as elegent as a scotch yoke, but would have lower friction and less load.
Regards
picclock
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Hi
in your first post you stated :
'I did calculations to ensure the ratio of swept volumes between displacer piston and power piston are almost the same - this is quite important as it largely governs the temperature difference the engine can run on, of course there are a lot of other factors but I think this engine should work'
If my understanding is right, this will result in a non running engine (its quite possible that I am incorrect as I have only recently started researching these). So please don't take offence.
Hi Picclock,
Thanks for the interest and your calculations. I didn't know that method for calculating an ideal ratio for efficiency, I did look into the maths behind it many years ago but can't remember any of it now so thanks for that. What I did know is generally, the lower the temperature differential, the larger the required ratio.
What are you saying would result in a non running engine though?
As I said, I calculated the ratio of Jan's engine and designed mine to pretty much match that. The ratio, if I recall correctly was 22:1.
Nick
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OK I see where I have gone wrong. In your first post where you say
'the ratio of swept volumes between displacer piston and power piston are almost the same'
you are referring to the same ratio as in Jan's plans, not the same displacement.
From my figures optimum ratio for 30C differential is 8:1. 22:1 sounds a bit severe, needing 12.5C differential for optimum efficiency. (edited due to bad math - See later post for a better understanding of this issue).
To me this gives the piston a higher average pressure over a much smaller diameter. Decreasing the ratio to nearer optimum will allow a more efficient extraction of the energy available. AFAIK, the closer to the optimim ratio, the better use is made of the available energy.
I'm quite new to this so my calculations may be in error, but on Jan's most recent coffee cup design he has a 100mm displacer and a 14mm power piston both being moved 5 mm. This gives an expansion ratio of 51:1 on my calculations (displacer=39250, power=769.3).
However, as I said before, I am still at the trying to understand :hammer: all aspects of this phase, so there may be reasons unknown to me why my calculations are incorrect :scratch:.
Just bought a couple of plastic tubs at Wilko's for experimenting with. When I get enough bits I will start a project log and try to figure it all out.
Best Regards
picclock
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Hi Nick, I was going to comment about the calculations but it seems that picclock has a fine handle on the important parts and what he says essentially covers everything except the friction parts, which are more easily dealt with by known materials, and experienced building, than calculations at this small size. I am largely unaware of modern versions of car engines, as I gave up that career years ago, and don't want it back. The VVT alters things as far as compression testing, but you still should have compression. As far as a valve in each cylinder being off its seat, it's either an automatic compression release, for ease of starting, in which case it is normal, or the strangest of coincidences, which I don't believe in, and am supported by the likelihood of piston meeting with said open valve in at least one of the cylinders, making loud funny noise. I know automatic compression release is becoming common in small engines and in some motorcycle engines, because they have to make so much power out of small volumes, and such engines rely on strong ignition spark because they lack on compression, for starting. I would start with checking to see if your engine does have compression release, and I'm assuming it cranks over relatively quickly as it ought to. I gave up on newer engines because I've spent all the money I want to spend on tools, and every new model needs new tooling, and new electronics to divine its problems. I get enough work from people who have engines most mechanics never even heard of before, because they weren't born yet, when the engines started the first time. No one teaches the old technology in schools. Can I suggest you buy an old Mercedes? I know this is :offtopic:, but my new to me 81 240D is running great and has no electronics, only electrics, which are like plumbing, to someone who once worked on radar. :lol: it gets good mileage too, and only cost me $1000 after my Buick got water logged with our recent flood. That's less than the difference between what our son gave us for the Buick, and what he still owes, since his car got flooded far worse, one of those low sitting Mustangs with water all in the wiring and the dash. If you've got one, put a timing light on one of the plug wires, and see if you've got spark at anything like close to the timing mark if it has one. If it were a head gasket, you'd hear the huffing and chuffing, and I expect the same if it were a problem with stuck valves. I hope you get this straightened out. mad jack
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Hi Nick
I think I've got a bit more figured out now. First a nice simple optimum ratio equation:-
optimum temperature differential = 273 / (power cylinder volume/displacer volume)
In Jan's design with a ratio of 51-1 the temperature change for optimum work is 273 / 51 or only 5.4C.
So why do Jan and others use such a high ratio, and optimise for such a low temperature differential ?. The answer is that during the time that the displacer is in a heating or cooling position, the maximum change of temperature that can be made to the working fluid is limited. These limitations are caused by the low thermal conductivity of the working fluid, and the small surface area available to heat/cool the fluid.
Which brings us back somewhat to my post in design ideas, where I suggested that if the displacer had a layer of pie tin foil (mmm Pies ::) ) on either side this would increase the area available to heat cool the fluid, allowing a lower ratio and making more power available.
Hope this helps to clear the waters I've muddied.
Good luck with the LTD and the car - seems like your due for some.
Best Regards
picclock
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Hi Madjack,
I'll quickly get the car issue out of the way - it's grown but still no further forward! There is indeed zero compression on all cylinders but the cam belt wasn't snapped - quite puzzling. It has something called a dephaser pulley on the inlet cam which moves relative to the shaft hence changing the timing according to throttle position, rpm and inlet pressure! I think the only viable explanation is that it's slipped around due to a faulty tensioner or water pump bearing and got drastically out of timing, pistons clattered valves and bent, sticking at least 1 valve open on each cylinder hence no compression. I can't confirm it yet as spend 1h30min trying to get rocker cover off, only to realise you have to take off wheel, inner wheel arch, crank pulley, timing belt cover, both cam pulleys then rocker cover! Anyway, it's a very sore point but the upshot is, the most cost effective and easiest way is going to be to get a 2nd hand engine (Ģ600ish) and swap it.
Now back to the project - I really want to start this but with the car in the garage, off the road that may become a more pressing matter! Another thought is, to save money - get on with this engine and it can be my dad's christmas present - I can't afford to buy anything more with the car fiasco!
Thanks for the further analysis picclock. Firstly, remember a lot of people designing / making LTD stirlings are trying to achieve an engine that runs from the temperature of your hand hence the large swept volume ratio and as you say, the large surface area to take on as much heat as possible. A lot of people make the cold end finned to transfer heat to the air but yours is a good idea of effectively creating a larger surface area on the inside of the hot end to transfer the heat to the working fluid.
Remember mine is based on Jan's new micro stirling, I guess there's another limiting factor hear in that you want to keep it tiny - I don't think Jan has thought about this in detail to be honesst but it seems his engine runs on something with a temperature of around 70 C so about 40C differential? so I thought if I maintain his ratio, mine should run as it is also larger.
It would be interesting to construct something with what the calculations show to be the most efficient ratio and see if it works on the designed temperature differential - I'm not sure I've got my head around the calculations properly. Surely a massive displacer with a large swept volume and surface area (assuming it's kept light) to take on heat would be able to drive a small power piston more easily than something with a smaller volume and area?
Jan has made an LTD and done some experiments - I roughly worked out it has a ratio of swept volumes of 52 and he says runs down to 8deg temp differential so they could be right. It's strange his smaller one with the 22:1 ratio needs a temp of around 70 degrees to run though or a difference about 40 deg. But is this due to something madjack illuded to - friction, which is probably much higher on the small engine in proportion to its power output - so it's something that can't be ignored in these calculations at least for small engines.
I see Jan on his website has done a 2nd improved version now, incorporating some of the same ideas as mine (I haven't shown him mine yet so he must have thought the same about the original). He has made his even smaller though instead of making it larger like mine!
Nick
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Well, I finally got a little bit of motivation and got in the garage to cut some metal tonight!
A slightly frustrating night but it has yielded 1 component - I started off collecting some materials together but then got bored of that so started turning the bottom displacer cover or hot plate as I've called it on my drawings. I quickly realised that because of the thin register I need to turn that and part it off a longer piece of stock. I have some cast gunmetal that I'm using. The slither that I had planned to use has now ended up as the flywheel! This means I've already deviated from my drawings, when I felt the weight of the aluminium I'd planned to use for the flywheel I thought it was too light, so I thought I'd use the cast gunmetal and thicken it up by 1/16" to 1/4" thick. The diameter has ended up as 1.22" or something rather than the 1.5" I had originally planned. Actually, this now seems a bit heavier than I thought so may have to do the ally one after all but maybe keep the 1/4" thickness, then it might be heavy enough.
Anyway, here it is:
(http://img.photobucket.com/albums/v287/NickG24/Tiny%20Stirling/2010-12-0323-46-56_0001.jpg)
The cake is 2nd hand, my 2 year old son licks the icing off but he didn't do a very good job on this one so waste not want not!
(http://img.photobucket.com/albums/v287/NickG24/Tiny%20Stirling/2010-12-0323-47-33_0002.jpg)
Feel a bit disappointed that that's all I managed in a night but at least it's done. As I said, it deviates from the drawing in size and material. I couldn't be bothered to find / change tools etc either so the recess isn't quite right. I think I will modify the drawing just to widen the alloy flywheel. Unless this one works then I'll change it to brass. The plan is just to loctite it to the crankshaft - just easier for this little engine, it'll have no power so won't come loose.
This is probably the 2nd most complex part on the engine so at least it's a start.
Nick
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That looks good Nick.Yer off to a good start. Despite the material decisions/ recycling. :thumbup:
You are tougher than me..... I've managed 3off, 20 minute sessions this past week. Before the fingers gave up. ::)
Angle grinding yesterday. REALLY didn't need the extra cooling draught it produced...... :bang:
David D
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Thanks David,
For some reason I didn't feel the cold actually - it must have been the coldest day for a long time yesterday, mind you, had long johns and thermal vest, then a fleece, jeans and overalls on so guessing that helped! Got a bit of carpet in front of the lathe too which helps. What doesn't help is the car sitting behind me with a half dismantled engine and bits everywhere to trip over!
Nick
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Did some more in the garage today - again, not as much as I'd have liked. More messing around sorting the parting tool out - it had remained in snapped form since I tried to part off some tough steel but I need it for this. I always struggle turning thin things like cylinder covers for some reason!
Not much progress to show, below is the hot plate or bottom displacer plate, the other side doesn't look as good as the parting tool was not on dead centre height so it left a bigger pip that it should of, then I had to file it down - no matter though as it's the underneath of the engine.
(http://img.photobucket.com/albums/v287/NickG24/Tiny%20Stirling/2010-12-0419-13-28_0001.jpg)
I have almost finished the top plate which is probably the most complex part - touch wood it's gone ok so far, it had to stay in the milling machine though as just got to drill and tap the hole for the upright then it's finished. I got a good fit with the register on the plastic tube so am confident it will seal well. just need to work out what sort of glue to use. Maybe some quick ish drying araldite?
Nick
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Lo Nick,
that sure is a small engine! If you need a heavier flywheel, you can solder three twopenny pieces together, and done... Iīd be likely to lose most of my ready made parts before I could assemble them together. Even if I kept them in a box, then Iīd probably lose even the box...
Gluing with Araldite will certainly keep the bottom and the plastic tube together. Even if you later on would like to get them separated :bang:
One possible alternative might be "Marston universal jointing compound", that you can get for instance, from
http://www.bengs-modellbau.de/werkzeug/werkstattbedarf/marston.php
Itīs not a silicone but polyurethane, and it never really hardens. Itīs easy to take apart if needed, and absolutely tight when in place. The page says itīs blue, but mine is definitely red... Good up to 250C°, at least. The excess (and the stuff itself when disassembling) comes off wiping with a rag with some spirit (ethanol, methanol). Iīve used it in several engines, for gaskets. Despite its English-sounding name, it is made in Germany (http://www.marston-domsel.de/index.php?id=173&L=2&L=2). You donīt need much of it. I bought some years ago a 20 ml tube, and have used it for many engines, when Iīve stripped and put them together again, many many times, during the years. And I still have some 3/4 of it left. It certainly beats silicone gasket compounds (or paper or Klingerite, etc.) in model engines, hands down. And the usual: No connection with Bengs MB, except a satisfied customer.
:wave:
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Hi Olli, I've just done some more and am now only realising the true size of this thing myself - what have I taken on here?! :doh:
Thanks for the advice on sealant, I will have to look into it, it would certainly be an advantage to have something that'll withstand temperature, although I'm not sure what the plastic displacer cylinder will go to! :scratch:
Got a bit more done today - I bet people can't believe this ... I've been in the garage a few days running!
Started off by finishing the top plate which is combined power cylinder and displacer rod guide on my version. All I needed to do was drill and tap the hole in the right position 4ba - how hard could it be?
(http://img.photobucket.com/albums/v287/NickG24/Tiny%20Stirling/2010-12-0514-23-51_0001.jpg)
Well, for me very hard apparently - I tried to be clever and tap it in the milling machine under power- normally I do it loose enough so the tap will spin in the chuck - not this time :bang: it stripped the thread straight out! :doh: At one point I was just considering loctiting the bolt in when it comes to assembly but then I realised the other bolt option I had got out was slightly larger- 4mm alen key screw. Won't look as good but it'll do the trick.
(http://img.photobucket.com/albums/v287/NickG24/Tiny%20Stirling/2010-12-0514-46-34_0002.jpg)
Next I cut the plastic tube to length, I gripped it in the lathe with a bit of nylon I found inside for support and parted it - worked fairly well, just needed tidy it up a bit with stanley knife, take little burrs off.
(http://img.photobucket.com/albums/v287/NickG24/Tiny%20Stirling/2010-12-0515-04-56_0003.jpg)
Unfortunately it's probably not as clear as it appears in the photo, it also has picked up a scratch on 1 side. On the plus side, it is a really good fit on the little registers on top and bottom plate and is actually just about air tight with no sealant at all, but think I'll use something at least on the hot end.
Next I decided to have a look around for some material for the con rods - I couldn't really find much, I had designed it 1/8" wide x 1/32" thick. I found some 1/8" x 1/16" brass strip and thought this would do. The little ends have a slot in them 1/16" wide so there won't be any clearance there - will just have to make sure there is a little. The big end journals are 1/8" wide so plenty of clearance there.
This was the point when I had to double and triple check my dimensions as it all seemed stupidly small!
(http://img.photobucket.com/albums/v287/NickG24/Tiny%20Stirling/2010-12-0515-55-43_0005.jpg)
That is the shorter displacer con rod, I have made the other too (see last photo). The only problem I see with these is whether I'll be able to get them over the crank or not - I was planning on turning that from solid. Hopefully they'll bend out enough to slip over then nip back with pliers. I annealed them before I made them to straighten them but may do again to be on safe side.
Here are all the bits so far:
(http://img.photobucket.com/albums/v287/NickG24/Tiny%20Stirling/2010-12-0516-33-08_0004.jpg)
Still got uprights, all rods and pins (they are just cutting to length though), crank, displacer and pistons to do.
Nick
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Hi Nick, you let other people play with numbers and glues and such, you're doing a bang up job on a tiny little engine and I can only wish I were ready to do the same. I'm really looking forward to seeing it run, now that I have it in proper perspective, that is quite a little beastie, and should be beautiful running. :jaw: mad jack
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Thanks Madjack,
Forgot to mention in the text, I did use some thin aluminium to protect it while it was offset in the 4 jaw to drill / ream the power cylinder hole but I must have gone a bit far - didn't want it to come loose so it still marked the gunmetal through it. :(
Never mind!
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Hi Nick, sorry, not clicked on this one for a while. It is looking a real stonker!! I`m really liking this and the size is crazy. I hope it runs for you - I`m sure it will!
Chris
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Thanks Chris,
I'm doubtful as to whether it'll run or not, I should have tried a much larger jobbie for an LTD as these look tricky at the best of times, but I fell in love with it when saw it and thought I could make some improvements to the design. Have you revisited yours yet or are you concentrating on the Stuart? I know you've been making those great puzzles too.
I wish I had made it from materials that would take heat - suppose I could always replace the plastic for some glass and some sort of high temp adhesive though if I need to. It's going to be a present for my dad so even if it doesn't run it should look ok - bit choddy giving your dad something that doesn't work though :lol:
Anyway, here is the latest instalment - no machining to show, all I did was cut / file / grind some pins to length and turn the displacer - I didn't have any balsa wood or really any wood I could easily turn so I thought i'd make it from nylon - had some 5 thou under the diameter I had planned so don't think that'll matter, I have no idea whether the material will work though! :scratch:
(http://img.photobucket.com/albums/v287/NickG24/Tiny%20Stirling/2010-12-0700-10-25_0001.jpg)
(http://img.photobucket.com/albums/v287/NickG24/Tiny%20Stirling/2010-12-0700-16-05_0001.jpg)
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Nick,
Sorry, I replied to your post over on HMEM.
I gave a few pointers that might help.
John
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Looking good Nick
Stew
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I have to smile, every time I look at this build Nick. :thumbup:
Fiddly diddly parts/ my fumbly fingers.... ::)
I'd have enough remade parts, stored under the duckboards/ in corners/ disappeared entirely, to make a batch quantity! :doh:
Blummin well done! Of course it will run! :clap:
David D
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Hi Nick, I'm keeping an eye on this one, the tiny ones are the hardest to get running, as the friction and power come closer to each other from opposite directions. With regard to the nylon, your biggest issue is mass, and if you can counter balance the mass of that displacer, the power piston only has to make it change direction, not lift it, so it's a matter of inertia rather than sheer power. If it's too heavy, you can drill many holes in it, and cover them with plastic film glued on. Moving the displacer is necessary, but it is the big energy drain the power piston has to provide for. I keep thinking of a well with two buckets and a rope so you only lift the water and not the weight of the bucket, and thinking about two tiny engines, with their displacers out 180 degrees and with the cranks connected, so all the parts counter balance each other. I'm really hoping you get this little engine running, it ought to, for your dad. :poke: by the way, what is "cold" there? I'm feeling it here, and it's 25 degrees F. :bugeye: On the car, I hope the engine swap goes well for you, and you find a warm day somewheres along the way, I know I don't look forward to engine swaps any more. That engine sounds like it has too many parts for its own good, all in all. mad jack
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Thanks for the advice John / Madjack - I will have another look around for more suitable displacer material. I think I might have some balsa wood round at dads - can't imagine it machining well!
John mentioned exactly the same over on HMEM. I was planning on putting a counter balance on the flywheel but as you say, this could make the moment of inertia too high - funnily enough I had just sketched the bucket scenario, you also have the power piston which is 90 deg out but that is pretty light. If I can't find anything else easily, skimming a bit off, drilling a load of holes and sealing with some film seems a good idea though.
It is pretty cold here at the moment Madjack, on the odd couple of nights it's been under minus 10 Deg C, apparently -14 Deg C one night! I put the thermometer in my garage the other night and it said 7 though so I doubt if it's been much under 5 in there.
Cheers Stew!
David, surprisingly in this cold, I've managed not to lose anything yet - I put the 2nd little pin in a pin chuck to de-burr after the first nearly went missing though! I cleverly (or so I thought) put all the bits inside the displacer cylinder with the top on so as not to lose them - today I thought I'd take the lid off to admire my work and the bits went everywhere! :bang: Was almost a disaster but managed to find them all - phew! :beer: I really hope I can get it running.
offtopic: On the car engine, that thing just gets stupider by the minute - apparently the problem could have been caused by a slipping crank pulley that drives the camshafts - to which I said, surely there must be a keyway - but no, there are no key ways on the engine, everything is controlled by friction and stretch bolts! So if somebody has torqued the crank pulley bolt wrongly or the bolt is passed it, the whole thing slips, pistons into valves and good by cylinder head! I can get an engine for around Ģ650 but as somebody said, it'd be kind of daft not to have the cambelt done before putting a 2nd hand one in - but that costs about Ģ400 due to 4 specialist locking tools you need - then there's the auxillary belt that drives aircon, alternator, power steering pump, water pump, tensioner etc - it's really just a nightmare. Somebody did point out that because of the model it is, it's prob worth about Ģ500-Ģ700 without an engine so that is an option I'll have to weigh up, just getting rid of it:offtopic:
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Nick, I can't offer you advise, but have been following along closely :) - That is a really small little LTD you're busy designing and building here :bow: :bow: - I really wish you success with it!
Kind regards, Arnol
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This is an interesting build Nick :thumbup: what a tiny little engine :bow:,
Ray.
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Hi Nick, good luck with the car, they always do it during the cold season it seems. The balsa wood should turn well if at high speed and with very sharp edges. I've got a book on LTD stirlings, and it suggests the use of styrofoam, and a hot wire to cut it. It focuses on a coffee cup sized engine, and suggests cutting out four holes in the displacer, like one would with a cookie cutter, and filling them with stainless steel wool, as "regeneration material, absorbing the heat of the air as it passes through to the cool end, and the air absorbing the heat right back when it returns through as the displacer moves the air to the hot end. I just thought I'd mention that although it would be a bit difficult with the size of your displacer, it would affect the efficiency of the engine overall. :offtopic: I am truly surprised to think there isn't a key or other positive locating device on such an important part, and sensitive issue in that kind of engine. I know also, I would never take an engine, sitting in my shop, and put it in a car without replacing a timing belt, given their propensity for shedding teeth. That whole thing sounds like a nightmare. On the other hand, I'm really looking forward to your success with your stirling, looking to see a video of it running. :beer: mad jack
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Thanks Arnold & Ray.
Thanks for the good luck with the car Madjack, I'm at the end of my tether with those, it's a good job I've had this stirling to take my mind off it. I did think about a regenerator but have never seen them used in an LTD, maybe it just doesn't make enough difference to warrant. I think I might try to lighten my nylon displacer and stick some very thin plastic over the holes.
I've been looking at the engine manual today and the whole thing is a nightmare- not helped by such things as power steering pumps and air conditioning compressors - I'm in half a mind to remove them completely, make my own idler pully and tensioner.
I'm hopeful for this engine but it is extremely small!
NIck
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.........I've been looking at the engine manual today and the whole thing is a nightmare- not helped by such things as power steering pumps and air conditioning compressors - I'm in half a mind to remove them completely, make my own idler pully and tensioner.
I'm hopeful for this engine but it is extremely small!
NIck
going :offtopic: (and deliberately misreading things) if you just caught this thread at this point, I'd be wondering what power density this mini-stirling generated to drive hydraulic pumps and an air compressor!
and/or will the project then develop equally tiny pumps and compressors ....
Dave :coffee:
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Hmm, good point Dave, I hadn't read that back but it was very misleading - apologies!
Might generate some more interest continuing on this theme though :lol:
Nick
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Dave,
If you do a bit of searching on the web, the Stirling has progressed a lot further than people think.
Only a couple of weeks ago I was looking at plans from a few years ago of the stirlings that were used in the Space Shuttle program. Mainly for refrigeration systems. Again, a few years ago, Japanese students had a fully operational (and compact) motor vehicle using both solar power and very low emission and highly economical fuels driving a sterling engine for it's main source of traction.
We are rather far behind on the design of things with what we do.
Bogs
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I was doing a little looking around for mini stirling engines on the internet and found this:
Stirling Engine Motherboard Fans Powered by Waste Chip Heat (http://gadgets.boingboing.net/2008/02/29/stirling-engine-moth.html)
Talk about hightech! A stirling engine powered by microchip heat and used to cool said microchip!
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Pretty impressive stuff Bogs!
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Got a quick update tonight. I only managed 2 hours work, not pleased with the results but nevertheless it yielded 2 iffy components :bang:
I set about making the 2 bearing uprights, one is was to be soldered (I think actually I'll glue it some how instead as I don't want to mucky up and have to clean everything) and the other bolted to aid assembly.
I started by finding some suitable brass, as luck would have it I found some 1/16" plate which is what I had designed it for - some 3/8" wide strip would have been ideal but this would be ok.
I made a bit square and marked it out, first mistake was annealing it - this made it black and difficult to mark out.
(http://img.photobucket.com/albums/v287/NickG24/Tiny%20Stirling/2010-12-1322-38-02_0001.jpg)
Cut the two ends off and filed to size, then put in milling machine to drill bearing hole. Mistake 2 - managed to drill off centre and using a blunt drill made a massive burr on the other side.
(http://img.photobucket.com/albums/v287/NickG24/Tiny%20Stirling/2010-12-1323-02-32_0002.jpg)
At least the hole was sort of square, but this is so thin I can just give the holes a bit more clearance to reduce friction if anything is binding anyway.
(http://img.photobucket.com/albums/v287/NickG24/Tiny%20Stirling/2010-12-1323-14-18_0003.jpg)
I could use this rod to help me hold them together while I filed one side to make the hole central again - got bored of this to be honest and it's already 20 thou undersize on width now - doesn't really matter but it's frustrating.
My marking of the radius on the top had now gone so I had to do it by eye - filing button would probably have been the order of the day here but for 1 rad on this thin bit of metal it was hardly worth it.
Here are the finished bits, even managed to drill the other hole off centre for the bolt too. A pretty poor night really, lots of scratches in it too. :(
(http://img.photobucket.com/albums/v287/NickG24/Tiny%20Stirling/2010-12-1400-07-48_0004.jpg)
Final mistake was that I forgot I'd used 4mm instead of 4ba for the bolt, therefore my clearance hole isn't big enough, which means I couldn't do a trial assembly. By the looks of it I still have a burr on the top plate anyway so that'll need to go first.
I should really have paid more attention to these, because the flywheel sits between them, they are quite visible. I don't have time to go back and start re-making parts now though, I think I'd rather just prove the design if I can.
Well, that leaves me with 4 parts to make ... 2 small ends, crank and piston. So 2-3 more nights at least, hopefully I'll be finished on Friday. I will probably need to re-make or modify the displacer though which will be too heavy.
When I was eating my bacon sandwich from the canteen on Friday it occurred to me that the box may be the sort of material people were talking about:
(http://img.photobucket.com/albums/v287/NickG24/Tiny%20Stirling/2010-12-1400-11-52_0005.jpg)
Or alternatively, the lid I stole from the fridge could be used to seal up my nylon displacer after I have attacked it with a drill!
Nick
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"Pretty poor night" , Nick? ...... I don't think so! :scratch:
Two off, shiny, adjustable components. Plus the lessons learned during their manufacture. :thumbup:
Also, thinking inside the box, while eating a bacon sarnie..... Who could ask for much more! :lol:
Hope things go even better for you this eve. :D
David D
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David, thanks for putting a positive slant on that - think I need to do that more often when I make rubbish! :lol:
:lol: Yeah, if it takes bacon sarnies to inspire me, think I'll do more of that in the future!
Hope so too, approaching the home straight now.
Cheers,
Nick
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Now thats odd, Nick, I was having a couple of bacon sandwiches the other night, and I got a great idea of what to do with a cylinder I'd bored and finned out of some cast iron, and fitted a piston to, but didn't have exactly what kind of engine it should be part of, chosen yet. Must be something about bacon, it's great for seasoning cast iron pans and pots as well. Must be some special brain food in that bacon, got to eat more of it. As David said, hardly a wasted night, just a bit of learning is all, and a couple of shiny parts to boot. :poke: mad jack
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Haha, it must be - will ask the wife to add some more to shopping list as I need some inspiration right now, instead of perspiration :lol:
:offtopic: Earlier I had a nice phone call saying the garage had sorted my other car that conked out, they've changed a couple of parts out of good will but the real problem was the use of supermarket fuels - strange nobody else has the problem I thought. Anyway, merrily went along to pick the car up and the light on the dashboard and fault came flashing back up before I had managed to get it into 1st gear! At which point my blood reached boiling point and I politely told them to shove it! I want them to exchange the car for something else, but it remains to be seen what they'll offer me for the car they don't know how to repair. That's not my fault, I can see this being a long drawn out argument. :bang: Meanwhile, back to my mum's volvo!
There's my excuse for not being in the garage - getting abit late now but I may go and do an hour, might help me unwind a bit
Nick
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Well, even though it was a late start, I did an hour and a half in the garage last night. Had to keep the momentum up! I started by lightening the displacer, drilled a load of holes, not right through and superglued some thin plastic over it. I don't know yet if it's enough, it's probably only 30% lighter. I was going to make a backup with some closed cell expanded polystyrene stuff from the bacon butty box, but as Bogs suggested, the glue I tried just melted it, so I'll need to get the proper stuff for the job or find some thicker material to make it from 1 lump.
After that I turned the piston from the graphite - that stuff gets into all the little scratches in your fingers and doesn't want to wash out! I found that the bore of my power cylinder is slightly tapered so it probably won't work. I reamed it so it shouldn't be the case, really I would need to ream to next size up but I only have the odd few reamers so don't have anything to do it with now. Anyway, I've turned a piston and it seems a reasonable fit but I can't really get a feel for it until the whole thing is assembled.
Remaining parts are 2 small ends - 1/8" dia brass with a hole drilled through, a slot in 1 end and a cross hole, and the crankshaft which is the most complex component. If the solid version fails I will have to build one up and loctite together I think, might be easier anyway.
No pics, not much interesting to see but will take some tonight. Night off tonight as am off to pub for a much needed drink. Just realised it's work xmas party on Fri night too so I'll have to get my skates on on Thursday.
Nick
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Hi Nick, I meant to get back to you on this, I've had the same problem with tapered holes bored. I ended up finding swarf under the back way of my carriage, and then found the carbide on the boring bar was a bit wrong angled for the material, and finally got straight boring the final cut with only a couple of thousandths, stopping the lathe with the cutter at the bottom, reversing the feed, and starting the lathe, cutting with no extra, back out of the hole. I got down to less than half a thousandth that way, but no way to change that except do some scrapping on the headstock and the bed. With an open ended cylinder, I hone out all the taper, and with brass, I'd use a piece of delrin or the like, to be softer than the brass, and fine carborundum in oil. For cylinders, it's best to have a long lap, at least twice the length of the cylinder, and a short lap, about half the length. You use the short one to remove local problems, and the long lap to even all the local work out. On brass, I end up using polishing paste along with a block of rouge, rubbed on the lap after the paste, and it leaves a mirror polish, good for graphite. The short and long lap method is really good when using graphite pistons, I learned it for doing hydraulic pump cylinders, and fitting new pistons in worn out ones. It is worthwhile to make your power cylinder with a head, just so you can lap out all the taper, particularly since you've got it on a base which can hide it. Hardwood dowel is good for laps in brass and aluminum too. I hope you Dad relished all the work you put into his gift, and will fully appreciate it when he gets one that runs. If you were around the corner, I'd lend a hand. :poke: mad jack
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Thanks for the info madjack, I just drilled and reamed my bore on this one as it was small but your comments are noted for next time I bore something properly. I don't understand why I got a tapered hole unless I had a tapered reamer, couldn't see any markings to suggest it was and I always struggle measuring reamers. I got a small set of new, common sized reamers for christmas so I should be able to achieve better results on things like this in the future. Also got a slitting saw arbor so thin slits etc should be no prob. I kept a couple of slitting saws from my horizontal mill.
Anyway, sorry I haven't been on for a while but this will be my final update on this version of the tiny stirling engine.
Here is a pic of the lightened displacer, as I said, it didn't make it that much lighter to be honest, maybe 30%. Apologies for these pics, I was just having one of those days and not a lot would go right!
(http://img.photobucket.com/albums/v287/NickG24/Tiny%20Stirling/2010-12-2319-38-32_0001-1.jpg)
Next was the piston as I said below, then the two small ends. I didn't have any 1/8" dia brass (thought I had some brazing rod but couldn't find it) so I made some square versions from some flat 1/8" brass strip. I also decided to make them a tad wider than 1/8" in the other plane so I would have more room for the slot. I selected the right drill to give a nice push fit for the pins so everything together with a pretty easy press fit. Here are pics of them assembled to rods. I was running a bit short of time by this point so sorry, I didn't get any machining pics but there wasn't much to show.
(http://img.photobucket.com/albums/v287/NickG24/Tiny%20Stirling/2010-12-2319-53-34_0001.jpg)
The last piece was the crankshaft. I started making this from 3/8" square brass and quickly screwed the diameter up resulting in a wobble on the flywheel before I'd even started on the journals. So that bit got scrapped, then I could only find 3/8" square steel. This was bought about 13 years ago for my 5" gauge Sweet Pea locomotive project that hardly got started. It actually cut nicer than the brass which I was pleased about.
This was a tricky component to make. I had to decide on the right order of machining operations so as to leave enough structural integrity so that it wouldn't bend.
The first job was to centre it in the 4 jaw. That wasn't too difficult as I found out 3/8" was the smallest size my 4 jaw would go down to - this became a problem later. I faced each end to overall length then turned the longer plain diameter for the flywheel and the 1/8" spigot for the bearing. Turned it around and did the same on the other end so each end was concentric (within the accuracy of my 3 jaw - good enough).
That's when I was going to put it back in the 4 jaw to offset turn the journals but of course I couldn't, the 4 jaw was too big, when I tried to get the offset the jaws just clash into each other.
So I decided on a fool proof way of getting the 1/8" offset to give me 1/4" stroke. I just put a bit of nylon in the 3 jaw, offset by 1/8" with a bit of packing under 1 jaw, centre drilled and drilled a hole for a tight fit on the plain diameter, then put a saw cut through to the hole along the length of the offset bush. I then clamped the crankshaft in the bush in the 3jaw. I was struggling to get it to grip the shaft but when I did, I took too big a cut and it mangled the nylon and pulled the shaft out - luckily or miraculously no damage. So I decided to make an alloy split bush instead by the same method. This gripped much better.
I turned the journal furthest away from the chuck first, then the one nearer in, as I said so it still had enough strength. This worked pretty well except I possibly got a little frightened as it was approaching 1/16" diameter and stopped a little large.
When I took the crankshaft out, it had turned out well except I don't think it had achieved the 1/8" offset I required. How could this happen? I just assumed if I put 1/8" packing under 1 jaw that would do the trick, or did I need to work some geometry out? I've never even thought about it to be honest!
(http://img.photobucket.com/albums/v287/NickG24/Tiny%20Stirling/2010-12-2319-37-07_0002.jpg)
This was on Christmas eve or the night before I think so I didn't have time to make a new one, I just thought I'd have to try it. The effect this would have is to leave dead space at the top and bottom of the displacer though - not good.
I thinkit was on christmas eve that I assembled the engine. Here are the assembly pics.
(http://img.photobucket.com/albums/v287/NickG24/Tiny%20Stirling/2010-12-2418-46-16_0002.jpg)
(http://img.photobucket.com/albums/v287/NickG24/Tiny%20Stirling/2010-12-2418-45-42_0001.jpg)
(http://img.photobucket.com/albums/v287/NickG24/Tiny%20Stirling/2010-12-2418-46-35_0003.jpg)
(http://img.photobucket.com/albums/v287/NickG24/Tiny%20Stirling/2010-12-2418-47-50_0004.jpg)
I forgot to mention, the other issue on the crankshaft was, I got carried away and forgot to make the journals the correct width. I thought ah, it'll be near enough jsut being the width of the parting tool - that way I only had to do 1 plunge for each. But it wasn't quite - When I assembled, one of the bearing uprights was to be super glued onto the top plate but to get it free running, I had to put a couple of shims under it to prevent metal to metal contact with the crankshaft and one of the rods - luckily I had allowed enough clearance on the length of the crank main bearings to allow this.
The other bit I found difficult was putting the rods onto the journals - these were the ones that had slits in the big ends to bend out, over journal and back in. With hindsight, I think I needed bigger slits. The plan was to bend them back with the long nosed pliers but I couldn't get in with those. I might have been able to do it resting on something and acouple of taps with a hammer and thin piece of steel. Not a great way of attaching the big ends really I don't think. May have been better building a crankshaft up of 3 or 4 bits but I thought I'd try to be clever and make from one piece!
The engine seemed very free running, I tried it on top of a flat bit on the heated towel rail and couldn't really get a peep out of it. It span over faster (10 or 15 revolutions) in the direction of running and only 4 or 5 in the opposite direction but nowhere near running I don't think.
Tried holding it over a tea light too and that was no different.
I think there are a few reasons it didn't run. The first, was the crank didn't have a long enough stroke leaving too much dead space in the system. Secondly, the fit on the displacer rod and piston could have been better. Thirdly, friction was possibly still too high even though I thought it was free running enough. The fourth could be the weight of the displacer, although the assembly seemed fairly balanced to me, it didn't seem to settle in any particular place. It had the weight of the piston and pin etc on the other side. Maybe the flywheel was also too heavy. If I make another, I will address all of these issues and hopefully have a runner.
I could provide drawings but I don't think anybody would want to risk spending the time and effort making something that might not work so I'll wait until I've built a working version.
My dad seemed happy with his present. Put a copy of the general assembly drawing wrapped up with it so he knew I'd design and built it with the intention of giving it to him for Christmas. I was gutted to have to give him a non working model though, if I do make a working version his will be swapped for it!
Nick
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Nick, looks great and even as a non-runner, it is a smashing model of a LTD stirling. I`m sure your dad won`t want to swap it and will appreciate the time you spent in making and drawing the plans up. It is nice giving something that you made, my dad really liked his puzzle I made him - I think Dads appreciate the time involved!
Just curious, did you do a water test and submerge it to see where the leaks were?
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Cheers Chris, glad your dad liked the puzzle. I think they do appreciate it but I still would have felt 100 times better if I could have showed him it running! I literally didn't have time to do any trouble shooting so didn't even do leak test but if I was a betting man I would put money on around the displacer rod and probably power piston. I think my seal between the tube and top and bottom plates was good as they were sort of a snap on fit and I glued them on too. When I first made the bits I blew into the holes unglued and there was no leak on the bottom, very slight on top which I assumed would be easy to stop with glue. I might do some trials with offset turning and what sizes I need to make the big ends for them to snap over the crank journals or think of a different method as wasn't happy with that.
Nick
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Nick,
Just a couple of pointers.
The first is that even though it doesn't run, you have learned a lot from your mistakes. Mistakes get remembered a lot longer and easier than successes, so you won't do them again.
The other is concerning reamers.
As far as we are concerned, you could basically class them as two types, hand reamers (including adjustables), and machine reamers. There are loads of other types, but for our use, just the two.
Hand reamers have a square on the drive end that fit a normal type of tap wrench, and machine reamers will be either straight shank for fitting into a drill chuck or morse taper.
The major difference (in this easy to understand text) is that hand reamers have a long lead in taper, up to 1/3rd of the length of the cutting edge in some cases, and machine reamers normally usually have only a very small lead in taper.
Where this is leading, is that you said you ended up with a tapered bore after using a reamer. Two causes for that if they are hand reamers, the first is that you used the wrong technique for cutting and you made the beginning of the hole larger because you wobbled about a bit, or the usual cause, you didn't penetrate with the reamer all the way thru, so didn't reach the parallel part of the cutting flutes, only the tapered lead in area. It is for that reason you can't use normal hand reamers in blind holes, the bottom of the hole will always end up tapered.
You don't usually get this problem with machine reamers, because they are parallel for almost all their length, but you can still end up with tapered bores, especially if your tailstock isn't exactly central.
A floating reamer holder solves most of those problems. A project for me that isn't very far off.
I hope this helps
John
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Hi Nick, I have been reading the whole thread once again, and figuring out what to suggest. But havenīt come up with anything obvious or show stopping. Itīs difficult to make remote diagnoses :doh:
That displacer seems to me rather heavy. Styrofoam, polyurethane, balsa, something a lot lighter would probably be better. The displacer rod also seems to be touchy. Itīs prone to leaking, and that will make quite a difference. The power piston leaking slightly wonīt be nearly as harmful.
The all-important thing is, it must be free-running. Reducing friction is far more important than reducing leaks. I guess the bearings are OK, but if you have any oil/grease(!) in them, you should wash it all away. With my engines, I rotate the flywheel back and forth in +/- 10o steps, through the whole circle, and listen and feel if thereīs any scratchy noises or stiffness anywhere. And do my best to find the causes, and reduce them as much as possible. If I give the flywheel a flick with my finger, the engines make some 8-10 rotations, accompanied by a "swoosh-swoosh" noise, coming mostly from around the displacer rod. I cannot make it completely airtight and still make the engine run. But itīs not a LOUD noise, barely audible, and it is more when the displacer is moving towards the hot end.
The engine might need a bigger heat difference. If you cooled the top cover, by putting some ice (snow... I guess that could be arranged... :) ) on it, it might show some vital signs...
Other than that, and without seeing/feeling it, quite hard to suggest anything. Wish you the best of luck with it!
:wave:
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John, many thanks fir the reply. Now that you've explained about reamers I think I've seen you explain in another post but I'd forgotten. This could very well be the case as it was a hand reamer I used, I don't think I wound it all the way through and the cover is relatively thick. My new reamers are also the hand variety but look a bit longer so hopefully will have a longer parallel section. I'll be sure to wind right through and use it as a floating reamer supported by tailstock if that's a better technique. Olli, thanks for the trouble shooting techniques, and the displacer material will definitely be as suggested by a number of people this foam next time. I will also try to lighten all of the rotating / reciprocating components. Cheers guys,
Nick
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Hi Nick, as John said, reamers are fickle things, and while one seldom finds a less than straight machine reamer, if of decent quality, one does get by occasionally. Most of the time, a machine reamer reams taper because it is held too rigidly, and for instance, my tailstock dangles about two or three thousandths, from sixty odd years of wear, so a proper reamer holder would improve their performance much. With regard to the eighth in shim in the three jaw, you effectively only moved the radius a sixteenth, this was the error I made in turning my cam in my Duclos flame sucker, twenty years ago, and prevented it from ever running until this year. Were I you, I would look for a piece of balsa wood to make the displacer out of, as that seems to be generally available in hobby stores, and it has been proven out many times. My wife hates it, but I have no problem digging in the "green boxes" and rescuing someone else's trash, if I see machine parts available, or scrap metal for stock. I only buy metal when I have to, but I've got tons of iron and steel from years of a machine shop, and quite a few hundred pounds of aluminum of various sorts. One should never let a printer or computer go in the bin without being disassembled, and all the useful parts kept. You might need to practice more scrounging :poke:, if you're going to build engines. None the less, it is nice looking, and I'm sure you'll get it all sorted out soon, after the holiday rush. :bugeye: :thumbup: mad jack
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Thanks Madjack,
I think I will have to wait until after the holiday rush! More car trouble and it's just becoming so annoying now. I managed to get the dealership to do a straight swap for the citroen that had all the issues with it for a Vauxhall Vectra SRi. Despite the dealership being a bunch of incompetent ***** I thought I'd got a good deal out of them in the end. I picked the new car up on Christmas eve, it was a year newer than the other and a petrol this time - 3 days later the engine management light was on on the dashboard, had a friend plug it into the vauxhall diagnostic (thanks to him as just doing that normally costs Ģ65 + vat!) and it says there's a fault with the 'cam phasing mechanism' - another engine with daft variable valve timing ... why does everything have to be so complex these days?! So I'll no doubt have more trouble getting that repaired and getting the dealership to pay for it, but they better do, only had the car 4 days!
I have sketched the thing with the 1/8" packing to get the right offset and I still don't understand why it wouldn't give me the right offset, surely you are just moving it 1/8" off it's original centreline by doing that, I can see that if you put it under 2 jaws it wouldn't move as much but just under the 1, shouldn't that have worked?
Nick
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I think you said you were putting 1/8" packing under one jaw of a 3-jaw chuck. With a 3-jaw, you only get an offset which is 2/3 the thickness of the packing, so 1/8" packing offsets by 1/12". If you want 1/8" offset, you need 3/16" packing.
It took me a while to get my head round it :scratch: :scratch:
There's an explanation of a sort three-quarters way down this page:
http://homemetalshopclub.org/news/aug03/aug03.html
Andy
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Actually, it's a bit more complicated than that. One needs to take into account the thickness of the chuck jaws. There's a program on my page (ECCENT) that will do all the dirty work for you.
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Actually, it's a bit more complicated than that. One needs to take into account the thickness of the chuck jaws. There's a program on my page (ECCENT) that will do all the dirty work for you.
Thanks, Marv. For me, life increasingly seems to be getting "a bit more complicated than that" :scratch: :(
I have had a go with ECCENT. Does the "pack to 1.5 times the offset" idea only break down when the dimensions of the work couples with the required offset are such that the work is not being supported by the flat faces of the "other two" jaws, but by their sloping sides, or are there other complicating factors?
Yours curiously,
Andy
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Yes, as the work loses full contact with the two other jaws the geometry gets more complicated.
The program accounts for all this automatically.
For round stock, the ECCENTUB technique is much more stable since the work is fully supported on all three jaws.
None of these techniques are as good as the old four jaw, however.
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Thanks Andy and Marv - I completely neglected the fact that with the packing, the jaws have to open further - I just don't seem to be thinking straight at the moment. Now I've come to think of it I'm sure someone has shown me that page before Andy, it's amazing all this stuff I keep forgetting! Marv, I'll definitely be using eccent for the next one, thanks. I guess you'd have to be careful with smaller stock as there is quite a radius on the gripping face of my jaws.
Nick
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Hi Nick, I just wanted to chime in, I have never crossed that page, and never really considered the whole issue geometrically, and thus my answer was wrong, as well. I've let the problem be an issue without ever solving it, and Andy was very helpful in clearing my head on this as well, if you don't mind my using your post to thank him. I think I will book mark that page, and have it when I need it. By the way, what program are you using to draw your designs with, if you don't mind my asking? I see them in the background and they look simple, but very nicely done. I wouldn't mind something more than scribblings on scratch paper, for drawings, sometimes intricate details don't get down on the scratch paper and get missed. By the by, with the LTD stirlings, the longer you make the displacer rod tube, the more effective it is in sealing, if you've got it reamed well, as John described, and if the rod is ground and polished. I don't know how far your Dad lives from you, but if you built the engine again, and fixed all the little issues it has, you could probably trade it out without letting him know, and let him have one that runs, after you work out all the bugs. I was hoping to do several presents this Christmas with small engines, but the flood sort of took up the past couple months, and I ended up with gift cards - nothing like the same. Keep posting and let's see a runner soon :poke: mad jack
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Hi Madjack,
I did the same as you, but at least you didn't just think sticking in packing the thickness off the desired offset would work! :bang:
The drawing package I use is called Alibre Design. It's free to download a trial version but there are limitations, then about a year or so ago an offer came up to get the full version for Ģ99 so I hmm'd and arr'd about it for a while and then bit the bullet. I am a design engineer by trade (although we don't actually do that much new design as such at present times) and at work we use a similar package called unigraphics which costs many thousands of pounds, but this little one seems to do all the basics just as well, and in fact it's more user friendly so for Ģ99 it was somewhat of a bargain.
It is a 3D CAD package - not sure whether you have come across these before but essentially you create each individual part in 3 dimensions (models) - starting with a primitive solid (cylinder or cube) or a sketch which is extruded, then adding bit by bit all the features to it. Once you have done all of the parts you then create an assembly or sub-assemblies if required and give them mating constraints to put them together - this comes easy for us engineering-y types because you think about how the assembly works and it gives you a clue as to what mating constraint you need. Doing this correctly has the advantage that the final assembly will be left with the correct degrees of freedom the actual model would, which means you can animate it - for example I can grab the flywheel on mine and turn it over, all the other pieces will turn over with it as they should in real life. This can show up if you've made a boo-boo and get contact, you can get pretty complex with it but I'm not a draughtsman so I try to keep it simple.
Anyway, once you've got the 3D model of each part, the package will then generate 2D views of that part and will automatically dimension them if you wish, I usually dimension myself as the system will probably do it any old how (probably in line with some convention or standard actually but not the way I would do it necessarily). As I said, I've kept my models simple, I haven't put any chamfers or radii on as all this transfers to the drawing and takes up more memory. Also, I don't have a plotter, only an A4 printer so for clarity I can't put mega detail into the drawing.
The reason I got the package is that my scribblings are just too scribbley for me to understand - I'll forget what I have scribbled! When I first got the package I ideally wanted to fully tolerance all the drawings so that anybody could make any part and it'd still go together and work - but that turned out to be a huge job and is not generally seen in model engineering.
Back to the tiny stirling, that was the idea with the thick top plate - the displacer rod guide is relatively long - as you say, helping with sealing, but the rod I had was not ground - just stainless I think and the hole was just drilled with the nearest number drill which I don't think was good enough. On my other stirling I just drilled the guide but It had a screw in bit so there was provision to put some graphited yarn in there and it was ground because it was 1/8" rod rather than 1/16". I'll have to see whether you can get 1/16" silver steel - can you get 1/16" reamers?
My dad just lives around the corner and I know where it is, in his glass book case so your idea is entirely possible!
I think I want to get back onto my poppin flame sucker / licker / gulper next and get those done which are not that far off - the broken machine vice stopped them, then I got :proj: and started jumping about. Then I'll re-visit the stirling as I think it's a nice design (if I say so myself) that other people could do if I iron out these bugs.
Thanks for the interest,
Nick
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Hi Nick, your reason for going with the drawing program sounds exactly like my reasons for being interested, some of the niggling little details occasionally get lost from the house to the shop. I'll take a look at the program and see what it looks like, working with it. I was once a pretty fair draftsman, many long years ago, but too much time in the machine shop ruined me.
A trick I've used when a reamer isn't around is to take a new drill bit of good quality, and with magnifying googles, stone a radius on each of the corners of the two cutting lips. With extreme care, getting both radii equal, it will work almost as well as a real reamer. They do have sixteenth in reamers though, and if you want, I'll look through my pile and see if I've got one. I bought a large assortment from the son of a machinist and it included many very small reamers. If I find one .062, I can post it to you, and some sixteenth drill rod as well, if you'd like. I'll let you know about the reamer tomorrow, after I've looked through my box. :thumbup: jack
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Many thanks for the offer Jack but please don't go to any trouble. If the reamer and drill rod are available I should have novtrouble getting them. Will have a look tomorrow. It's worth a try of the trial version of that software and keep an eye out invade the offer comes back up.
Nick
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Hi Nick, I don't have that reamer, but my catalogs show reamers down to 3/64ths, and I definitely have drill rod that is a sixteenth, so it is available. If you do have difficulty getting such a reamer, let me know and I'd be glad to help out, no problem at all. mad jack