Author Topic: Building another Stirling  (Read 31841 times)

Offline cidrontmg

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Re: Building another Stirling
« Reply #50 on: November 29, 2010, 07:31:05 PM »
Well, thank you all for your comments, I didnīt think it would go this quick myself. Iīve done a few engines, and usually  (=every time except this one) they have given more than enough labour pains. BUT - itīs not "finished" yet, although it runs (or at least limps). It sorely needs another longer displacer piston + tube. As it it, it wonīt run very long, some 15 minutes, and then the displacer cylinder gets too warm, and the music stops. It gets too warm exactly because it is too near the heat source. The glass tube extends now some 30 mm from the ali top, the original idea was something like 70 mm (=over twice as much!). I expect with that modification it will run "forever". And have far more power and speed.
Also I should point out that Iīm retired, so I have more time for the shop than anyone with a daily work. And with the weather mostly rainy, even a naturally lazy guy gets some things done.
Proof of which is the new lamp I put together. Rainy day, once again.


The thing started as a tea light (candle), itīs made of tinplate (iron, basically), and it has a lid, with a glass window. I soft soldered a curved 6 mm tubing to it, made a small cap for the tube (to keep the spirit from evaporating, should there be any left from running). And pulled the wick into the tube. This has a far bigger flame than the other, with a 4 mm tubing for the wick. 4 mm outside = 3 mm inside = 7 mm2. 6 mm out = 5 mm in = 19.6 mm2. Not quite, but almost three times. With this lamp, the small engine really spins!
The lamp being of iron is handy in that you can fix a magnet to the base board (a round neodymium just needs a drilled hole), and it will keep the lamp from moving with the engine vibration. Thatīs why the base in the small lamp is a round steel stamping. Although I admit that all-brass lamps look nicer...  :)
Thereīs more to come, but not tomorrow!
 :wave:


Olli
Penafiel
Portugal

Offline cidrontmg

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Re: Building another Stirling
« Reply #51 on: December 01, 2010, 08:45:56 PM »
Fat lady doing a duet.


 :wave:
Olli
Penafiel
Portugal

Offline Stilldrillin

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Re: Building another Stirling
« Reply #52 on: December 02, 2010, 03:55:30 AM »
Blummin well done Olli!  :clap: :clap: :clap:

Love the slower revs of the big 'un.....  :thumbup:

David D
David.

Still drilling holes... Sometimes, in the right place!

Still modifying bits of metal... Occasionally, making an improvement!

Offline arnoldb

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Re: Building another Stirling
« Reply #53 on: December 02, 2010, 12:06:42 PM »
Blummin well done Olli!  :clap: :clap: :clap:

Love the slower revs of the big 'un.....  :thumbup:

 :clap: :clap: I agree fully with David Olli

 :beer:, Arnold

Offline madjackghengis

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Re: Building another Stirling
« Reply #54 on: December 03, 2010, 12:16:01 PM »
Well Oli,  it looks like you've got it running, and done a very nice job in getting it so.  I expect your experience with parts fulfilling your original expectations will make it run better and with more power, and make it a matter of full satisfaction.  For the moment, they run very well, and certainly show your fine labor in bringing them about.  I really like the glass for the displacer cylinder, and the brass/aluminum combination for looks.  Good job all the way 'round :beer: :jaw: mad jack

Offline cidrontmg

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Re: Building another Stirling
« Reply #55 on: December 05, 2010, 07:51:43 PM »
Well, Iīve been fiddling around with the engine, done some slight changes, and come to the conclusion that itīs "good enough". I first made another crank disk, with even less throw, itīs now something like 13.5 mm. And cut some half moons away for balancing. The con rod is still a bit too heavy, have to drill holes in it. And round it closer to the M3 head.




Then I made a little bit longer "core" for the power piston, so that the Teflon mantle comes closer to the cylinder top. When I shortened the crank throw, it of course didnīt go all the way to the top any more. Now it does.
Then there was the overheating. To improve cooling, I cut the fins in the displacer cylinder some 1.5 mm deeper. There was (and still is) material enough. And what do you know, it now keeps on working for as long as it gets its rum ration. Iīve run it for over an hour non-stop, no signs of heat death. It just keeps on choogling. Even with the pudgy glass cylinder. And with a very brisk pace also. At least as much revs as the small engine does. What it needs though is copious amounts of spirit (=heat) - a huge flame. The displacer gets way hotter than in the small engine, but it doesnīt seem to be any cause for worry. The O-ring obviously gets even a bit hotter, but itīs still the original, and no signs (or smells) of it burning. Also the glass cylinder is holding its own, but it has started colouring red.


Iīve seen the same phenomenon in some photographs of German test tube Stirlings. Canīt say what is the cause.
I also changed the flywheel to the "original" ali thing. With the brass flywheel it would also run well, but slower.
And made yet another Teflon bushing for the displacer rod. That seems to be a sensitive point. I now left it a bit bigger on the outside, so that I really have to press it hard in its hole. And that seems also to tighten it around the rod better, itīs now quite air tight, and still very free to move.
Thereīs no Teflon tape in the power piston grooves any more, just the original mantle. What Iīve found is that oiling anything in the engine will not improve things. The Teflon piston should be as clean as possible. I often wipe it with a rag wet with alcohol, similarly clean the cylinder, wipe anything away from the displacer rod, etc. The Oilite bushing seems to slowly emit an oil film on it - no oil is definitely better.
So now Iīm left with a number of Stirling "spare parts", and wondering what to do with them...
One idea would be something like this - but I donīt have 4 extra test tubes... Just three. (First picture)
Another nice engine would be like this, except FAR bigger...  (see the match for scale in the Second picture)
Or maybe not a Stirling at all.
Thank you all for the encouragement and interest! I just might post some more pictures for this thread when Iīve had enough of blinging the lady, and mounted it to a proper base board.
 :wave:


Olli
Penafiel
Portugal

Offline madjackghengis

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Re: Building another Stirling
« Reply #56 on: December 07, 2010, 10:05:22 AM »
Well Oli, I have to say if fifteen minutes isn't long enough, then my flame sucker is a definite disaster, having eaten out four cylinders and six bronze pistons, with an average run time of a couple minutes, and needing work on it every five or six times I run it.  As soon as I get the graphite piston done, along with a graphite valve, I hope it will run long enough to stop working on it, so I can use the one test tube I found in my box, which is about half an inch in diameter.  I think you chose right in calling it "good enough", it certainly runs, and well, so don't spend too much time fiddling with it, you know you've got lots of other engines just waiting to escape out of your mind and hands.  Good job all the way around :headbang: mad jack

Offline NickG

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Re: Building another Stirling
« Reply #57 on: December 07, 2010, 10:44:22 AM »
Well done Olli, both fantastic engines. What's next then?  :poke:
Location: County Durham (North East England)