Author Topic: Jan Ridders' Simple LTD Stirling Engine - craynerd build log  (Read 51648 times)

Offline raynerd

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #25 on: August 10, 2010, 11:45:59 AM »
Hi Nick, the recess in the plate is on the piston side, the base is totally flat.



This is actually called for in the plans as the recess allows the displacer cylinder walls to sit inside it and be glued/sealed in place. The only difference is, I started with 6mm thick ally and left the walls this thickness instead of the 3-4mm in the plans. I have now reduced it to whatever the plans say so I`m back inline with the plans!

Chris
« Last Edit: August 10, 2010, 11:54:20 AM by craynerd »

Offline raynerd

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #26 on: August 10, 2010, 05:21:58 PM »
A quick update… last night I sealed the cylinder to the top plate:


and then I sealed the side of the displacer onto the top plate:


This evening I managed to cut the counter weight but I have to admit I struggled with this. At one point the flywheel was clearly falling to the bottom weighted position. The instructions, as I read them, was to keep trimming material from the weight until the flywheel landed at random positions. After quite a bit of material coming off the weight, I did get to a position where it became a little more random but it still favoured one side – I am concerned the power piston brass centre is too heavy as it is this falling to the lowest position which is causing the flywheel to end up at one side. That said, it isn`t as bad as it was so I`m hoping it is balanced correctly. If it doesn`t work it`ll definitely be my first “check”.
All the bits together and a picture of my trying to balance the system without the bottom plate.


And now the bottom plate sealed in position:


I guess the proof will be in the pudding when I try it out tomorrow when the sealant has gone off! 

Offline sbwhart

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #27 on: August 10, 2010, 05:47:03 PM »
Looking good Chris

If you use ER collets on your mill you can use them for drilling that will give you more head height.

Stew
A little bit of clearance never got in the road
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Offline raynerd

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #28 on: August 11, 2010, 02:53:08 AM »
Hi Stew, yes I have a set of er32 collets so I guess your right, it`ll give me a little more height but still think it`ll be an issue.

It is 7:50am, I awake with my alarm call (daughter shouting she wants to get out of her cot), dashed downstairs to put it on a hot cup and coffee.

and.....

It doesn`t run !    :( :( :( :( :( :(

Humm, it does seem to be pushing itself around a little bit... OK, I`ve a few things to check now. All I can say right now beginners with B ands rhymes with hugger.

Offline raynerd

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #29 on: August 11, 2010, 05:18:18 AM »


Is it just me or does it look like it is having a bit of a push behind it? Look at the first spin, the last two revolutions seem to get a "kick" ??

I`ve sadly ammended the first concern I had, that being the yoke to the power piston was too heavy and I`ve sealed it properly. Sadly, still no joy :(

Any thoughts or suggestions. I`ve also lifted it up and tried it in various positions and still no go.

Chris

Offline NickG

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #30 on: August 11, 2010, 07:23:19 AM »
Chris,

This nearly always happens with Stirling engines and I've heard LTD are notoriously difficult to get to run.

If you're confident of the seal between top and bottom plates I would start by taking the flywheel / frame assembly off, leave the the displacer piston rod in, submerge the displacement cylinder in water and blow into the power cylinder to see if any bubbles come from around the displacer piston rod. If it's a good seal there shouldn't be any, or very little.

It sounded like the power piston was a good fit in its cylinder, does it move very very freely because it needs to. The displacer rod also needs to run very very freely in its guide. What is the clearance between the displacer piston and cylinder wall? You don't want any unnecessary drag caused by friction or too small a clearance.

Finally, the crankshaft needs to be extremely free running. if you spin it over with nothing connected it should keep spinning for about 20 seconds.

Hope this helps, I know how difficult it was trouble shooting my stirling and flame gulper but if you take a systematic approach you'll get there.

Cheers

Nick
Location: County Durham (North East England)

Offline raynerd

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #31 on: August 11, 2010, 07:25:10 AM »
Removed the bottom cover and re-balanced the system. I think I did this correctly yesterday dispite my concerns and so things haven`t changed at all.



Now, call it impatience, I call it experimenting but I sealed the bottom plate on again and with the sealant still tacky, I put it on a hot plate. The sealant started to buldge out as the gas expanded inside the engine....does this tell me that the system is well sealed and also, more importantly that I have a good seal on the power piston and displacer bushing?!?

What could be wrong ...  :smart:
« Last Edit: August 11, 2010, 07:33:40 AM by craynerd »

Offline raynerd

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #32 on: August 11, 2010, 07:33:03 AM »
Chris,

This nearly always happens with Stirling engines and I've heard LTD are notoriously difficult to get to run.

If you're confident of the seal between top and bottom plates I would start by taking the flywheel / frame assembly off, leave the the displacer piston rod in, submerge the displacement cylinder in water and blow into the power cylinder to see if any bubbles come from around the displacer piston rod. If it's a good seal there shouldn't be any, or very little.

It sounded like the power piston was a good fit in its cylinder, does it move very very freely because it needs to. The displacer rod also needs to run very very freely in its guide. What is the clearance between the displacer piston and cylinder wall? You don't want any unnecessary drag caused by friction or too small a clearance.

Finally, the crankshaft needs to be extremely free running. if you spin it over with nothing connected it should keep spinning for about 20 seconds.

Hope this helps, I know how difficult it was trouble shooting my stirling and flame gulper but if you take a systematic approach you'll get there.

Cheers

Nick

Hi Nick

Thanks for the reply, we were typing at the same time! But if you look at my last response you`ll see I`ve ensured the system is balanced and I think you`ll see from the video that the crank seems to be freely moving. I`m happy with everything... I`ll have a bit more of a play once the sealant has gone off again. My main concern, and perhaps I should have changed it just now when I had the bottom plate off, but the displacer piston has a gap of about 1mm - 1.5mm. I know this is uneven but it is due to the foam board not cutting quite as clean as hoped in the end. Perhaps the 1.5mm gap is too large. The plans do state balsa wood but I know foam board is used. The plans also call for only 5mm thick balsa and this is quite thin, I know most stirlings take up a lot more of the displacer cylinders volume up with the piston itself!! Perhaps if after a little more fiddling I can`t get this to run, I`ll turn to the displacer cylinder and change that. Thanks for the support and advice..I appreciate it!

Offline Brass_Machine

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #33 on: August 11, 2010, 03:12:21 PM »
Chris

I have no advice as I haven't built a LTD Sterling (yet!). Keep plugging at it though... you are bound to get it.


Eric
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Offline Dean W

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #34 on: August 11, 2010, 07:23:47 PM »
Chris, here's my take on your first video;  I think it's making a little power.  When you rotate it CCW, it seems to
try to make a little go of it.  When you rotate it CW, it appears that the engine doesn't want to go that way, and
just from looking at it, seems to be making power enough to try to "push back" when turned the wrong direction.

When the glue dries, try it again.  Use a little more heat to see if it will make even a bit of a show at working.  If it
does, you probably just have some tuning work to do in the area of the crank bearings and alignment of the crank
journals, and in tracking down friction in the power piston and the displacer bushing.
It may have been my imagination, but I think I heard a squeak a couple of time when you were spinning it. 
Squeaks are a pretty sure sign of friction on some point.

Sometimes it just takes a while to sort these out.  The first one I made took me many hours to get running,
mainly because I didn't know "how much is too much" when it came to friction.
The last one I built started on the first flip.  
You'll figure it out!  Keep at it.  (BTW, the balance looks quite good.)

Dean
« Last Edit: August 11, 2010, 07:26:58 PM by Dean W »
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Offline Stilldrillin

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #35 on: August 12, 2010, 03:19:13 AM »
Chris,

I think the word is, perseverance.......  :thumbup:

You are so close..... You will have a runner!  :)

David D
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Offline raynerd

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #36 on: August 12, 2010, 03:26:11 AM »
Well it is back open again. The only thing that I wasn`t 100% happy with was the displacer piston. I`m going to get some fresh material for that and replace it, seal the unit back up again and then concentrate on mods to the top of the engine to get it running. Fingers crossed.

I was proud of myself last night, I opened it up and started making a new displacer. Things were going wrong so guess what I did.... yes, I managed to leave it and put it down for the night...  :med: :med: :med: :med:  I couldn`t believe myself!

Offline sbwhart

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #37 on: August 12, 2010, 03:36:50 AM »
Keep at it Chris you have all the basics for a runner you just have to slowly work at it and tease it into life, your at the point that we all arive at with a new engine of really learning about it, making the engine is only part of the story, getting it running is the last and most important chapter.

Stew
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Offline NickG

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #38 on: August 12, 2010, 07:32:09 AM »
Not far off now Chris,

I think your gap of 1mm around the displacer piston probably was too big so it'll be that and friction that are your enemy. Sorry I haven't seen your videos yet but as Dean says, try more heat or a couple of ice cubes on top plate. I had to do the ice cube trick on my stirling to initially get it to run, which helped troubleshoot.

Something else that isn't easy to see but just worth checking, is there definitely 90 degrees in your timing? Things can slip / move etc.

Nick
Location: County Durham (North East England)

Offline madjackghengis

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #39 on: August 24, 2010, 12:25:32 PM »
Hi Chris, I just watched your balancing video, and it seemed to me you are a bit tight on the bearings there.  I've not built an LTD stirling, but studied them a bit, planning on one, but I have lots of experience balancing shafts in ancient military radio and radar equipment, and the flywheel should coast more I believe, yours seems to stop rather certainly and not just drift to a stop.  Another thing, the use of the foam seems to be standard these days, but punching out holes in the displacer, and inserting stainless steel wool, boiled clean, as a "regenerative material", accumulating heat as the displacer moves down, and being a very poor conductor of heat, giving it back up to the air, as the displacer moves up, is also supposed to be a substantial improvement in efficiency, with about a third of the displacer area being replaced by the stainless wool being the norm.  Friction is the main enemy in any event.  good luck, I hope to see a running video instead of a balancing video, next. :nrocks: mad jack

Offline raynerd

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #40 on: August 24, 2010, 03:35:56 PM »
Yes, me too MadJack. My lathe is currently burried under tools while I re-organise my workshop .I should be finished tidying by weekend and I`ll try again then - I think I needed a break from it anyway.

You know the steel wool - how does it stay in? I can imagine the stray whisker popping out and causing a problem!

Thanks for the motivation. I`ve not given up, just a short break!

Offline NickG

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #41 on: August 24, 2010, 04:58:39 PM »
Just seen the video Chris and it's almost running! Not far off at all, I had a Kontax one like the one David D showed us earlier in the thread and the moment of inertia of the flywheel on that was way higher than on yours  - wonder if that has much bearing on how easy it is to get them to run - possibly better with a higher moment of inertia although obviously the ones with CD's for flywheels have been proven to work too.

Did you try some ice cubes on top plate? I think it might run just with a bit more heat, it's nothing more than fine tuning any 'tight' spots and possibly that displacer.

Nick  :thumbup:
Location: County Durham (North East England)

Offline madjackghengis

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #42 on: August 26, 2010, 10:08:42 AM »
Hi Chris,  the steel wool must be pushed and prodded into shape so it basically holds its own shape, with the holes in the foam providing a perimeter, and taking a needle or fine set of tweezers and weaving stray fibers back into the pad with some super glue to get the last stragglers to stay in place.  I'm curious, have you run an indicator around the test tube power cylinder and checked it for oval and taper?  I'm not sure how the test tubes are made, but I'm pretty sure they are not a ground finish inside, and you may well have less than a good piston seal.  I've got an "air-pot" dashpot, which is a ground glass cylinder with a graphite piston, intended to act as a shock absorber in some sort of electronics equipment, I got it as a "free sample", by mailing a card in, and the piston will stay at the top of its cylinder for hours with very little discernable drop, if the port is plugged completely.  It takes about twenty four hours to drop down if left totally alone.  If all else fails, I would try using conventional lapping techniques and lap out the power cylinder with perhaps a wood dowel lap, and very fine carborundum lapping compound, which is also a rather good way to see exactly how straight and round a glass cylinder is, as well.  I've found with my little flame sucker, it can easily be a dozen problems all at the same time stopping it from running, yet needing each and every fix, and not allowing a single one go undone and still work.  I questioned whether the new cylinder with actual head fins was necessary, after fixing everything else wrong, and put the old cylinder back on, with all the other problems still fixed, and while it was better than previous, it still did not even try to run, and immediately after putting back the new cylinder, it ran the first time I spun it over.  The only thing making me certain it was my problems, was the fact I've seen an engine exactly like mine, but with a quarter inch bore and a seven sixteenths stroke with a quarter next to it for size, just sitting there running a few thousand rpm like it was no problem.  I hope to see your LTD engine running like a top, soon.  I'm sure you'll get it all worked out, and you will know exactly where you fixed the most important impediment when you get to it. :thumbup: mad jack

Offline cidrontmg

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #43 on: August 26, 2010, 12:00:28 PM »
Heh, MadJack, not trying to steal craynerd´s thread, but the head fins in the flame licker are vitally important, like I told you elsewhere... 
I can´t be of much help with the LTD, having never built one myself. Although one is in my projects list. But from the videos it seems that it´s actually producing some power, but not enough to sustain the entire 360* rotation. So, you need more power, and less losses. More power= bigger heat differential, "tighter" power piston. Less losses= reducing friction in the bearings, linkages, wherever it might feel tight. Just one thought. Instead of a CD, I might try using an old hard disk platter, for the flywheel. They come in two varieties, metal and glass disks. Either one would have far greater a momentum than a polycarbonate CD.
And I´m sure you get a runner, it´s not missing much.
 :wave:
Olli
Penafiel
Portugal

Offline madjackghengis

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #44 on: August 26, 2010, 12:26:22 PM »
Not to steal this thread myself, but I must admit you were absolutely spot on, with regard to the head fins, cidron, and as a matter of fact, I took the engine and mounted it to the cylinder head of a ten horse Tecumseh engine which died, just to get the extremely greater heat dissapation the head fins give, and the engine runs essentially till I shut it down.  I would second that motion for a hard drive disc for the greater flywheel weight and effect, the videos both show the engine is very close to running, and just lacking the last little bit.  Powdered graphite is sold for use in locks for doors and such, and a tiny bit on the displacer shaft and in the power cylinder could help a bit.  As cidron says, you are definitely close to having a runner. :headbang: mad jack

Offline raynerd

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #45 on: September 26, 2010, 08:04:17 AM »
Well, I hate to be defeated but this has beat me. I`ve spent hours and hours on this and still no luck. I`m sure it`ll be something obvious, there have been attempts when it felt like it wanted to "go" but could never quite pull itself around. So, sadly, it has the same fate as my other attempt and to the shelf it goes..... unless I can tempt anyone to have a quick look at it for me and give me your opinions and perhaps a bit of time..???... I`d pay for P&P both way!!
I`ve always wanted one of these and I`m gutted to see it not running
Chris

Offline rleete

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #46 on: September 26, 2010, 09:04:58 AM »
After seeing your last post, I went back and looked at the thread from the start.  I think you are very close.  Your balance looks good, but I think it's deceptive.

You have way too much friction in the system.   That flywheel should turn over many times with a flick of the finger before stoping.  It should also "coast" to a stop, as madjackghengis observed.  Thses things have next to zero torque, and will not overcome

Loosen thing up a little, and I'll bet you find that your balance is still a bit off (but close), and that it will run after you dial that in.
Creating scrap, one part at a time

Offline raynerd

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #47 on: September 26, 2010, 02:55:58 PM »
The crank seems free running in the pivots, I feel any friction is coming from the power piston and more than anything, the displacer rod bush - if I free them up I`m worried then I`ll have air escaping! Hummmm...  :( :( :( :( :(

Offline madjackghengis

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #48 on: October 08, 2010, 11:57:04 AM »
Hi Chris, if you'd like I'd take you up on the checking it out, but I fear the postage would be a killer for you.  I've just gone through your build log and this is what I see, and I'll try to keep it in order of priority.  First, I have no confidence in your cylinder.  Test tubes are not ground and lapped, so it is not round nor straight, I would almost guarantee.  The fix is to machine a piece of polycarbonate or some other hard plastic to just barely fit in the cylinder, put some grooves to hold lapping compound, and I would rub rouge on it, lapping it longitudinally, while rotating the lap back and forth, and if the cylinder is true, you will get even lapping evidence throughout the cylinder.  The best lap would be one longer than the cylinder, probably twice as long or a bit more.  You can "prove out the cylinder by coating the piston with prussian blue, and pushing it down in the cylinder and pull it out taking care to avoid any turning or side pressure.  If the cylinder is round and straight, you will get at least a 75% transfer of blue and it will be evenly spread with the 25% max, being spots disconnected from each other.  Knowing the quality of test tubes from experience, I wouldn't even bother, but would lap the cylinder from the start, and if you can't get the one in place out, break it out, after you've lapped a new one, and are completely happy with it.  Your lapping is done when you've got as near 100% cross-hatch as you can get, but you must ensure no dirt or dust gets in the lap.  You can also turn a piston out of some plastic or metal, just for the use of testing your cylinder in place, making it just barely fit, and using it with the prussian blue.  Secondly, once you are sure you have a perfect cylinder or as close as possible, you will need to turn a new graphite piston, but it will be easier this time, because your cylinder will be more accurate and a better gauge than the last.  Your trunion in the piston should be as small as possible and aluminum for mass purposes.  Third, you should have little discernable friction in the graphite displacer rod bushing unless it is cocked, or under pressure.  Once reamed in line, there should be no discernable friction there.  Fourth, your connecting rods should be loose enough on their pins to have no discernable friction there as well.  The possibility of excess glue on the pin is something to investigate for and you should be able to feel any friction when turning the connecting rods around their respective crank pins, and there should again, be no discernable friction.  If they are just a little snug, a bit of shaking side to side while rotating them around their pins should move sufficient metal to relieve any friction if there is no glue, and the pins are truly round.  Next, the main shaft, with no connections, but rods freely moving, should be turned not by the wheel, which gives enormous mechanical advantage, but removes any slight "feel" you might get, but turn the shaft in your fingers by the end of the bare shaft, or somewhere in the middle, where your fingers can judge any force necessary to overcome friction.  Again there should be no discernable friction here as well.   There seemed to be some in the main shaft from your videos, but that is not as good as feeling it, so I may be wrong.  A little loose is better than dead on, if you put your two respective "cranks" together with the main shaft running through both side plates of both cranks, and sawing out the middle of the shaft, once the pins were glued in, it should be in line.  If you didn't do that, it is quite possible each crank is performing its own elipse, and causing the excess friction.  If this is the case, I'd re-do the cranks, putting all the cheeks in their proper respective places on a single piece of shaft, gluing the pins in place at the same time as gluing the cheeks to the shaft, but only after getting all aligned and in proper timing to each other, and giving over night for the glue to set, so you don't disturb your accurate setup while cutting out the shaft between the cheeks of the respective cranks.  At this point, I would mount everything but the flywheel, with the connecting rods attached to the displacer rod and the piston, and turn the shaft with your fingers pinched, to get the best feel of what actual friction you will have accumulated.  It should almost be free enough to have momentum past spinning, even without the flywheel.  If it does, then it is time to mount the flywheel and balance it.  If it does not, as per my own experience, you must find where the friction has crept in, and it will be in one of the places you've just been through.  It will most likely be a niggling little thing, such as a slight bend in a connecting rod or a pin where it connects to the displacer rod or the piston.  Spinning it with light machine oil on the metal to metal bearing surfaces with a drill motor at a moderate speed so as not to bend the crank from the inertia of the displacer, should free up any friction in the shaft at this point.  Once the flywheel is balanced to compensate for the mass of the displacer, it should run, as those are all the essential points absent the basic concept of a stirling, the sealing and good heat transfer.  A "dashpot" made for many purposes in both electronics and in vacuum control circuits is commonly sold which is a ground, lapped and polished pyrex cylinder, with a fitted piston is commonly available here, I expect you can find similar there looking up "dashpot" as the key word, if you wish to avoid the work of fitting the power piston, however there is no reason you can't equal what they do, if you start right.  For a new cylinder, I would put a piece of hard plastic round stock in the lathe with double the length of the cylinder sticking out, machine it to a snug fit and spin it in the lathe, working the test tube cylinder back and forth on it until is moves freely.  I'd either split the plastic, or mill our a section half way through, in the middle of the working section of the lap, before using it, and take another piece already turned to the exact same size, and mill half of it away, and drill for two pins to hold the two parts in alignment, with the pins fixed in the main part of the lap, and then, once the cylinder tube is free on the lap, adding a piece of fine cigarette paper between the two parts of the lap to expand it, and continuing, doing this each time the cylinder gets free, before it gets loose, and continuing until you have an even lap as close to 100% as you are willing to work it.  The displacer rod bushing should be reamed to exact size, and if it is a two part bushing, both parts in place for the reaming.  That should eliminate any friction in it.  I supect your piston and cylinder is the power issue, as you can probably tell.  The lapping of the glass cylinder can also be done with a hardwood dowel, however I've had problems with warpage once I've cut one, because of grain patterns, that's why I recommend the plastic rod.  I believe it is acetal or delrin I've used, not polycarbonate.  Delrin is very cheap and easy to get, so I would go with it.  I hope you can find some use in this, I'd hate to see you shelve a project with the labor in it, you will someday look at it and have to fix it anyway, that is my own experience. :poke: :scratch: jack

Offline NickG

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Re: Jan Ridders' Simple LTD Stirling Engine - craynerd build log
« Reply #49 on: October 09, 2010, 02:04:11 AM »
Chris,

just to give you an idea of friction required, not sure if you've seen Jan's troubleshooting tips on his other LTD page here http://heetgasmodelbouw.ridders.nu/Webpaginas/pagina_koffiekop_jan/koffiejan_frameset.htm

Notibly though, "The unloaded fly wheel must rotate for at least 4 minutes after you gave it a firm push by hand" and "With only the displacer coupled to the fly wheel this rotating time must be at least 15 seconds" finally "With coupled displacer and working piston this rotating time must be between 5 and 10 seconds (10 to 20 strokes)"

there are also guidelines on permissible air leaks, I would strongly recommend you look at that page, following his guidance was what got my stirling running.


Nick
Location: County Durham (North East England)