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cylinder for hot air engine

crack in thin wall tubing

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russell21/03/2010 23:45:08
142 forum posts
hi all,
 
i am (attempting) a simple stirling engine, from plans in popular science (april 61). It calls for a displacer cylinder of 1"  conduit turned down to 0.010 wall. I am using a piece of old bicycle frame. However, as i turned it down, i found a crack along the seam.  (about 1/2" long).
 
Is it reasonable to attempt a repair? I could silver solder, braze, or weld (oxy), probably using a scrap of tube as filler.  as its not the power cylinder, absolute concentricity doesnt seem important.
 
(I dont have any more tube from this source, and i would suspect that another piece would be just as likely to suffer the same defect, my first attempt i crushed in the chuck, the second i turned too thin and found a crack in that as well)
 
 alternative sources of suitable tubing  (in australia) welcome.
 
( i am planning on using an old asthma 'ventolin' inhaler as the displacer piston, its a little narrower than specified, is that a big problem? )
 
Ian S C22/03/2010 10:26:56
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7468 forum posts
230 photos
Hi Russell,I know the problem, had it myself with water pipe, started boring and it popped open, V'ed it out and a run with the arc welder, the engine is running ok, it was the power cylinder. If your OK with gas welding that would be good.The "Ventolin" canister should work although not ideal, I'm just picturing it, the ideal lenght is approximately 3 x the diameter. Another similar size cylinder is one of the old aluminium starter cans for fluorescent lights. Another one is old electrolitic capacitors,they come in all sorts of sizes. As long as the gap is'nt much more than 2mm all round it should be ok. There's another thread a bit farther down and 3 or 4 of us get on there and anoy each other-tell each other how were'r getting on, drop in anyway,see ya mate. Ian S C
Circlip22/03/2010 10:57:26
1723 forum posts
Another source for power cylinders, with a smooth bore are automotive shock absorbers, Rissos books on simple hot air engines give a variety of sources for components, worth a look.
 
   Regards  Nother Ian.
russell22/03/2010 11:26:43
142 forum posts
thanks Ian SC, guess i'll give it a go welding. i am sort of afraid i'll weld up that section, and another gap will open up when i go a bit further. live and learn!
 
the plan dimensions are 3 1/2 inch by 1" (external) - the inhaler is 22mm x 62mm so i figured it was fairly close. (there are some other inhalers which are a bit shorter).
 
thanks circlip, i picked up an old gas strut (i think) may be a great power cylinder!
(i also have a timing belt tensioner from a honda odysey, looks like a cast iron cylinder with piston, not sure how to get into it though)
 
 its all more fun than cutting the grass...
 
regards
 
russell 
Ian S C22/03/2010 11:38:59
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7468 forum posts
230 photos
I,v got one with the displacer cylider made from a cat food tin, and a displacer made from a Coke can. the power cylinder was one I made for another engine, and the flywheel is 5 CDs. It runs on ball races salvaged from a VHS tape machine. Russell if you live in/near town get to the library, I know the larger libraries here in NZ have quite a number of books on hot air engines,mind you the University here in Christchurch runs a course on hot air engines to Doctrate level, so there is a bit of interest. Discarded drive shafts are another place to find larger tubes. Ian S C
Mark Smith 325/03/2010 18:11:05
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175 forum posts
36 photos
you'll probably find that the cause of the cracks is where the tube was welded in the first place. I salvaged some tube from an old chrome-molly bike frame, it didn't need turning down as it was very thin to start with. Also different parts of the frame were a displacer fit.
Mark
Ian S C26/03/2010 09:38:01
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7468 forum posts
230 photos
Hi Mark, Malvern A&P show tomorrow, nephew is comming out from town so I'll hitch a ride with him and take the Ross Yoke engine up and give it a run. It won't have the radiator, but thats OK. Russell one thing I nearly used for a hot cap on the Ross Yoke Rider engine was the steel case from a D size Ni Cad battery, it might be just a little short for a displacer, A C cell is about 1" dia, and the usable part of the case about 1 5/8" long. You don't really have to go to 10thou, it just takes a bit longer to get to temperature/also takes longer to cool down. If you can get it, and manage it stainless steel is the ideal because of its reduced rate of conduction, it can be a bit expensive unless you'r lucky. Ian S C
Francois Meunier27/03/2010 22:35:13
30 forum posts
6 photos

I did this model some years ago, and it worked (and is still working) a treat. This is indeed a first class plan. The diameter of the displacer and its cylinder are not so critic as long as the gap between them is kept at about 1 mm. The displacer came from a Hupmann cigar aluminium tube and I did the displacer cylinder to fit, from a part of a steel tube. It was more easy this way since displacer are much more difficult to find (I don’t smoke!) than steel tube, which fill a large part of my workshop. Look also if you can find those large felt pens with an aluminium body, generally replaced now by an ignominious plastic bodyI never had the problem you mention with cycle frame tubing. I was amazed on the opposite by the quality of this stuff, a seamless steel tube. The extremely penetrating noise during boring is frightening and it takes a long time to bore accurately about 100 mm.

About the same plan was republished (Popular Science, July 1965, p106-110,176. & cover picture), the burner being replaced by a mirror to catch sunrays.

I’m very pleased by this engine, which run at 1200 rpm on a simple alchol burner, I can post pictures or videos if you wish.

Best regards

FM

Edited By gedeon spilett on 27/03/2010 22:52:57

Francois Meunier27/03/2010 22:35:13
30 forum posts
6 photos
Popular Science, July 1965, p106-110,176. & cover picture
Ian S C28/03/2010 11:28:28
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7468 forum posts
230 photos
Hi Gideon, I have made a displacer an its cylinder out of one piece of steel water pipe, the cylinder by boring, and the displacer by first boring to smooth,placing it on a mandrel, then turning down the outside. Got a friend (not a modeler)who as an engineer developed a solar water heating unit back in the 1970s, he obtained, and still has a hot air engine with a parabolic reflector that he used to demonstrate the power of the sun. I'v run my largest motor with a large fresnel lense. The kids at school can supply all the aluminium bodied felt pens I'd ever need (they use them on white boards instead of chalk and black boards), I'v used one, they are about 16mm dia maybe a little less, but now replaced by stainless steel. I know about the tendancy for boring bars to chatter( screach),if you want a half decent finish you'v got to stop the noise. Mark I went to the show, two chaps from the Historic machinery Club also went, but we did'nt display anything(it was too cold to stand around). Ian S C

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