Author Topic: Building another Stirling (Read 54025 times)

cidrontmg · « **Reply #25 on:** November 21, 2010, 12:29:41 PM »

Some more. I rounded the base board corners. I don´t have a "proper" tool for this, so I took a wood router bit, it has carbide tips, so it´s all OK with aluminium. Took several passes, small chips everywhere... Ran the mill probably faster than at any time before.

I also polished the board, tool marks and scratches incl. And the rest of the stand. They can now be put aside for a while.

Then it was about cutting the air passages in the cylinder supports. In the platter that goes next to the cylinders, there are two holes for passing the air to the cylinders, and a channel uniting the holes. In the other platter, there´s just the channel. I used a bit of scrap ali to hold the platters in the mill vise. Drilled and tapped some M4 holes in the sacrificial bit, and attached the platter with some screws. And drilled the M4 (so far) holes.

And milled the channel

Here´s the two plates, and the ali "jig" to hold them.

The displacer cyl. will have a hole that aligns with this hole. It will go straight "up" to the bottom of the displacer cylinder. The hole for the power cylinder in the previous engine needed a bit more complications. There is a brass pipe that goes right through the cooling fins towards the cylinder top. There is a horizontal hole, bored into the cylinder top, that unites this pipe and the cylinder. And then the hole in the cylinder side was plugged with a small piece of ali. You can see the said pipe and the ali plug in the other engine, in here. It´s sort of "hidden", not too obviously visible. But it´s there.

In this engine, there´s a separate cylinder head, so the brass pipe will pass right through along the whole cylinder, and also go some way into the head. And then I´ll mill a channel in the cyl. head to pass the air above the piston.
More when there´s more

NickG · « **Reply #26 on:** November 21, 2010, 01:18:56 PM »

Thanks Olli, now I know how it works!

Nick

cidrontmg · « **Reply #27 on:** November 23, 2010, 07:02:45 PM »

Some more photos. I drilled the hole for the tubing alongside the power cylinder, and milled the hole in the cylinder head. The tubing end protrudes slightly into the head.

Then there´s need to open up the holes in the cylinder support plates for the power cylinder, to create space for the connecting rod. Not much space above the lathe ways, but enough. I drilled it to 20 mm. The piston will be 19 mm (cylinder bore = 19.05mm = 3/4"), so it can enter freely.

And then bored the cylinder to 18,5 mm, and opened it with a 3/4" reamer. I don´t have a drill chuck nearly big enough to hold 19 mm, but the reamer has a centre, so no big problem. You can see there´s a homemade handle to facilitate turning the mandrel by hand, and slowly feeding with the tailstock, a lot of cutting oil, a spanner holding the reamer from turning, it worked quite well. The bore is straight, uniform in size, and with a rather good surface finish.

I had a slight change of plans. I was intending to use graphite for the power piston, but turning graphite is a messy business. The graphite bar is 20 mm dia, so about 1 mm needs to be turned to dust. It´s not terribly much, but...
So I was thinking about a Teflon piston. Or rather a Teflon wrapper around an aluminium core. Teflon is also a very low friction material...
I turned an ali bar to 12 mm dia, 23 mm long, and made 10 mm deep hole with M4 thread into one end. And turned a 23 mm stump of Teflon to 19 mm dia, with a 12 mm hole in one end. And pressed the two together. Rummaging in my scrap bin, I found a 70 mm long 6x6 brass bar, and bingo! - a con rod. Unfortunately it was some 4.5 mm short...
I also found a bit of 13 mm bronze bar. I turned the bar to a nicer(?) shape, and milled a 6 mm slot in it.

And soldered the two together.

Now the con rod is long enough. I made a small brass piece, 6 mm dia, with a M4 thread to go into the piston, and a flexible joint with the con rod. So there´s the power piston as it now stands.

There´s a reddish tinge on the Teflon, don´t know why. But it´s really snow white. The bronze "big end" really is rather reddish, clearly different from the brass. I turned two thin grooves in the Teflon, and wound them full of plumber´s Teflon tape. Not that it´s really needed, the piston has a good compression even without it. But it seems to wipe away "something" from the cylinder bore, and it can be easily replaced. And the compression "fine tuned". The stroke is 20 mm, it will be the same also in the displacer cylinder.

The power piston now breathes freely through the tubing, and with a hefty flick of a finger on the flywheel, it turns something like 22-23 revolutions (a bit difficult to count). If you block the tubing, it just bounces back and forth, not even one full rev. So there´s still some hope - it hasn´t jammed solid yet...

NickG · « **Reply #28 on:** November 24, 2010, 03:25:27 AM »

Olli,

Nice work. I was wondering about the use of teflon for a piston but I bet it's more difficult to achieve a good fit than with graphite? I suppose the heat won't be (hopefully) much at the cold end so it should cope with that ok. It sounds like you've got a good seal but a high compression ratio - it shiould be a fast runner provided there's enough volume of air heated to overcome the compression, or rather you heat the air enough.

Nick

Stilldrillin · « **Reply #29 on:** November 24, 2010, 04:37:41 AM »

Olli.
Some time back, I used PTFE for the 5/16" diameter pistons, in a special Mamod steam engine.

When the steam hit, they expanded by around .0025", jammed solid........ Modified, to a thinner PTFE sleeve, still gave .0015 expansion.....

I think you will have to experiment, even at Stirling temperatures......

The experiment was a success....... The engine is still performing as hoped for, with it's new owner, in Australia.

David D

cidrontmg · « **Reply #30 on:** November 24, 2010, 07:52:26 AM »

Hi Stilldrillin, NickG,
I haven´t used PTFE for a piston before, so it well might not be a good idea, but still worth trying. I can revert back to the graphite (I still have it...) if it´s a no go! I just didn´t feel like turning graphite right then. I had other engagements that evening, and didn´t want to show up there looking like someone just rescued from a coal mine... I´ve turned graphite a couple of times, and it makes an awful mess. At least it did with me!

Experimenting is certainly in the books, that´s the main reason for building this engine. I also want to experiment with other displacer sizes and materials. And balancing the engine, etc. Teflon and graphite, although both very low friction, are quite different as to thermal expansion. Graphite-not at all, PTFE-plenty. In this particular Stirling type, the work cylinder always stays cool, so I hope PTFE will behave. If not, too bad, and on to something else.

What I´m worried about now is balancing the engine. That connecting rod is sturdy, but boy is it heavy! Drilling holes in it (or grooves) will make some difference, but I´m afraid not nearly enough. Taking off some material from the crank disk will also make a bit of difference, but still not enough I think. Lead weights opposite the crank pin... Might be...
Thanks for watching, more on the way.

cidrontmg · « **Reply #31 on:** November 24, 2010, 10:34:39 PM »

Not much. Did another flywheel to experiment with. Rather, it was an old brass flywheel that had an 8 mm hole. Too large, the crank axle is 6 mm. I guess I could have done a split taper fit, but it also had a smallish hub, nowhere near the +/- 22 mm needed (the engine will have a 20 mm stroke). So I made a plug, cut a 5 mm disk of 30 mm brass bar, and soldered them together. Then I cut two lobes away with a 2.25" face and side cutter (and didn´t take pictures

)...
And then Loctited the plug in the flywheel (green goo in the picture). It´s now waiting to harden, will drill and ream it tomorrow. And probably drill (again...) 5 holes to make it lighter.

Stilldrillin · « **Reply #32 on:** November 25, 2010, 02:06:03 AM »

Crisp work Olli!

Mine never looks so good.......

David D

cidrontmg · « **Reply #33 on:** November 25, 2010, 11:45:38 AM »

A few bits more. I cut some glass. I first cut the flared portion off the test tube, to get a feel how it works. Not too well, seemingly, because I broke the flared end... This doesn´t seem to be genuine Schott glassware, although it´s branded as Duran. Or maybe Schott has a factory in China... So a bit more care, and another trial cut. I just need 78 mm from the bulb, and there´s 200 mm of it. Better this time, but not good. One more cut, this time with feeling, at the right length. Third time lucky, seems like the real McCoy. The cutting tool is next to the pieces, a "Dremel" diamond disc, definitely made in ROC. This is still the first test tube, I bought two.

The tube needs a hole in the displacer cylinder, so it had to be bored to size. The piston rod is 6 mm, and now I have bought some more silver steel (drill rod), and there will be two Oilite bushings to guide and to seal it. The displacer will be some 25-26 mm dia, the glass tube is 27 mm inside, so the rest of the displacer must be bored also to 27 mm.

There must also be a small step (+/- 10 mm long) for the test tube to enter, its outside is 29 mm.

And enter it does.

Test tube in place, with the O-ring, and a bit of silver steel with the bushings.

Bushings pressed into the displ. cylinder.

And another mockup. Seems to be rather square and reasonably well aligned.

It´s not missing much, the displacer proper and its connecting rod. Might run during the weekend. Or maybe not...

NickG · « **Reply #34 on:** November 26, 2010, 03:33:27 AM »

yep, nearly there Olli

, I'm confident it'll run - your machining looks spot on.

Nick

madjackghengis · « **Reply #35 on:** November 26, 2010, 11:04:41 AM »

Hi Nick, that engine is really moving along, and should be running here, shortly. Cutting glass is always a bit dicey, I've had good success with thin tubes by wrapping a cotton string around and tying it off, then putting some lighter fluid on it and lighting it, and hitting it with some water when it is about burned out, cracking it off pretty cleanly where the string was. Some care with a propane torch, taking lots of time to heat up the edge evenly very slowly, and the edge can be melted to a nice round profile, and eliminating cracks from starting from an unfinished edge. I always practice on the throw away piece because I never can be patient enough until I've cracked on before sucess strikes. I'm wanting very much to find a couple of test tubes myself, with all this inspiration. That ought to be a fine running engine when you're done with it.

mad jack

cidrontmg · « **Reply #36 on:** November 26, 2010, 04:00:50 PM »

Hi madjack, the way you suggested (with a "burning string") is also good. I cut the tubes for the previous engine that way. For the other engine, I bought 4 test tubes (showing great confidence in my glass cutting abilities..). I cut them all that way, all broke exactly where intended.

It´s also a very good idea to "polish" the cut edge with heating. Slowly is the key word, and careful... I overheated one of the tubes, and it instantly began to creep. See the left side on the pic below. It´s not round anymore

The tube is usable, there´s tolerance enough in the cyl. bore. But if it ever comes into contact with the ali cylinder wall, it´s fairly certain to crack. Borosilicate glass develops hairline cracks very easily, it doesn´t shatter to small pieces.
I went to cutting with a diamond disc, although the burning string method works very well. But I also wanted to try if I can cut an opening in the cylinder side. Haven´t tried that yet, but I will

Test tubes usually can´t be bought one off, they come in lots of 10-50. Not that it matters much, they´re cheap(?) in bigger lots, and you often need more than one

One source for single/a few tubes is
http://www.bengs-modellbau.com/material/buildingmaterials/index.php
they´re in Germany, the same site in German http://www.bengs-modellbau.de/
the German site is far bigger. Good quality, lots of hard-to-get things, and they send very fast. No connection except a happy customer

cidrontmg · « **Reply #37 on:** November 26, 2010, 09:42:26 PM »

The end in sight. The only piece missing is the displacer, and that has caused some head scratching. Seems I don´t have (and can´t quickly arrange) 25-30 mm aluminium tubing.

So what else is there... Plastic - no. Wood - no. Some heavier metal - ehh, no... A cigar case would be just about ideal - except I don´t have one that big. Might need a Robusto- or even Gordito- size. I have some cigar tubes, but the biggest is 16 mm dia. Not nearly enough.
It is of course possible to make a tube from a solid piece of bar. Starting with a 30 mm, and making swarf and throwing away some 95% of it just doesn´t sound good. Hm. What comes nowadays in aluminium cases... Even many cigars come now in plastic tubes...
After rummaging through some accumulated and increasingly unlikely trash (it tends to accumulate...), I hit the jackpot. An electrolytic capacitor, quite old and most likely dried up years ago. Outside dia. = 25.5 mm. Hehe. Just what the doctor ordered.
So I opened it up, by turning a bit away in the lathe, and stripped it of its (dried up) innards. It turned out to have massive amounts of rock-hard asphalt inside. I cleaned it away with paint solvent, and got just about everything out, but it was a struggle. I then turned an end cap for it.

British made even. And then glued the end cap in place with Loctite. And it´s a nice fit in the tube also.

So tomorrow, I´m going to finish it. I think I´ll wipe the texts away, and polish it slightly. There´s a few dents in it, but I hope it will do. At least until I get some bigger cigars in ali tubes.

There´s also the need for a bigger spirit lamp. I´ll first try, and hope it will work with the smaller engine lamp, but of course this engine needs its own. Back to scrounging the scrap buckets...

madjackghengis · « **Reply #38 on:** November 27, 2010, 09:31:43 AM »

Hi Oli, that capacitor turned out to be a nice fit, and leaving the printing on it leaves something interesting for people to wonder about, so that was a good job. Looks like you should be down to the end pretty quick here. I take it the test tubes hold up well to heat and you don't have to order special ones. I want very much to have an open and visible displacer, just to add another visual component to the engine, but the only tube I have is tiny, only about half an inch o.d. I definitely need to order some test tubes of substantial size. I like very much the way you have the power cylinder and the displacer cylinder side by side, I think it makes a very good looking engine. I'm looking forward to seeing it run.

mad jack

cidrontmg · « **Reply #39 on:** November 27, 2010, 10:39:13 PM »

First setbacks, one minor, another major. The displacer piston (the electrolyte cap.) is, I think, too short. I had to cut the glass cylinder (twice) to get it short enough. The piston should almost hit the cylinder bottom, and also almost hit the glass cylinder, at the resp. dead centers. Now it does, but the glass cylinder is a stump. Not looking good.

I´m fairly certain I´ll have to make another piston and cut the other test tube. It might work as it is, but there´s a bigger problem.

That (displacer) piston rod leaks furiously. When I flick the flywheel, it goes swoosh, swoosh, with the power piston going up or down. I made sure that´s where it leaks, with soap suds.

As you might remember, there are two Oilite bushings to guide and to seal the piston rod. They seem to guide it well, but the seal is non-existent. No wonder the piston rod was so very free to move... In the previous engine, I used the same construction, except the piston rod is 4 mm, here it is 6 mm. And in the previous engine it works perfectly. Blast.

I didn´t think that would be a problem... Now, I´ll have to push the bushings out, and then make a tighter bronze bushing (not Oilite). The piston rod I think I´ll keep, it was quite hard (sic) to make. I have a 6 mm reamer, remains to be seen if that will finish the bushing airtight, but still freely moving.
Another possibility would be a Teflon bushing. The Oilites are 10 mm dia and 10 mm long each, so there would be 20 mm to give guidance to the rod. Should be enough. Or maybe use one Oilite and replace the other with Teflon. This will need some experimenting. But it certainly won´t even attempt to run with that kind of a leak.
So it ain´t over till the fat lady sings. And she hasn´t started yet.

NickG · « **Reply #40 on:** November 28, 2010, 04:04:31 AM »

I get the impression there is always something extra to do with these engines Olli, nearly there though.

Nick

Stilldrillin · « **Reply #41 on:** November 28, 2010, 04:06:32 AM »

Quote from: cidrontmg on November 27, 2010, 10:39:13 PM

So it ain´t over till the fat lady sings. And she hasn´t started yet.

Don't worry Olli.

She's poised, and tuned up!

Setbacks are character building, I'm told.......

David D

cidrontmg · « **Reply #42 on:** November 28, 2010, 06:12:09 PM »

Well, the fat lady just started singing (but she´s not finished yet). She sings so loud that the table shakes (the engine/flywheel is still largely unbalanced).

Some more pics.

This shows the shorter power stroke.

Changes since yesterday: Pushed the Oilite bushings out, and substituted one of them with a Teflon bushing.
Changed the (=made a new) power piston connecting rod. The old one might have worked in a well-balanced engine, but it was too heavy (I told you...).
Shortened the power stroke, drilled and tapped another hole in the crank disk. The displacer volume is now so much less than intended that it cannot push the power piston all the way through the power stroke. There´s still a mismatch, but at least it runs, sort of.
I will make another much longer displacer piston, and cut the other test tube to size. Maybe also lengthen the displ. stroke. And make another spirit lamp. I temporarily pulled the wick out from this lamp, so I could get a bigger flame for testing (and filming). But this engine needs a lot more heat than the smaller one. And of course will consume more alco, so the itsy bitsy burner is a bit ridiculous.
The engine so far makes lots of noise, that also needs some tlc. The other one is very silent.
The flywheel(s) must be balanced. As it is, it will promptly walk off the table.
And general blinging might be of benefit..
My son will go to London next week, and he promised to get me a cigar in a one inch tube. I just need the tube, but I will smoke that cigar also

Always nice when a new engine behaves.

Thanks for watching, more when there´s some significant changes.

Reckless_Engineer · « **Reply #43 on:** November 28, 2010, 06:36:06 PM »

She runs

A great looking engine too! Ive been thinking of building a stirling engine and this thread has only helped to further convince me!

Rob.Wilson · « **Reply #44 on:** November 28, 2010, 06:40:59 PM »

Nice one

sweeeeeeeeeeet runner

Rob

Brass_Machine · « **Reply #45 on:** November 28, 2010, 07:57:06 PM »

Quote from: cidrontmg on November 11, 2010, 10:59:09 PM

...
I probably won´t be making this in a hurry, so be patient...

Ummm... 17 days isn't hurrying?

Very nice build BTW. and she is a runner!

Great job.

Eric

Stilldrillin · « **Reply #46 on:** November 29, 2010, 02:02:02 AM »

Quote from: cidrontmg on November 11, 2010, 10:59:09 PM

...
I probably won´t be making this in a hurry, so be patient...
Olli!

Quote from: Brass_Machine on November 28, 2010, 07:57:06 PM

Ummm... 17 days isn't hurrying?

Very nice build BTW. and she is a runner!

Great job.
Eric

My thoughts too Eric!

Quote from: Stilldrillin on November 12, 2010, 03:58:00 AM

Good luck Olli......

I'll be patient!

David D

I was prepared to be very patient, if necessary. Now, I'm clinging on by my fingertips.....

Blummin well done Olli!

David D

NickG · « **Reply #47 on:** November 29, 2010, 05:11:26 AM »

Well done Olli - it's brilliant!

Brass_Machine · « **Reply #48 on:** November 29, 2010, 10:54:50 AM »

17 days... from stock to runner... very very nice. I am impressed.

Eric

arnoldb · « **Reply #49 on:** November 29, 2010, 11:33:43 AM »

Wow Olli - you pulled this one off quickly! VERY nice

Sure beats the heck out of the fat ladies I've heard singing!

Arnold

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Author Topic: Building another Stirling (Read 54025 times)

Rob.Wilson