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Sterling engine piston matl.

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Eric Cox21/08/2010 10:39:07
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I recently started to put together a Sterling engine kit I received last Christmas. The displacement piston was made by wrapping a fine metal mesh around a wire frame. unfortunately my cat decided to see if it was edible. I contacted the supplier for a replacement and received a pad of wire wool that turned out to be too flimsy to form a piston. Any ideas on what material I could use.  
Ian S C21/08/2010 12:29:43
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Hi Eric, good to see another hot air engine builder. I'v built about a dozen engines, some based on the design of others, but mainly to my own design. I,v read of the type of displacer that your engine uses, allthough have not used it myself yet. The idea is that the steel wool is wrapped around the central shaft of the displacer, presumably retained by a disc of some sort top and bottom. When first fitted the steel wool will rub on the inside of the cylinder, but on the initial heating the steel wool will soften, and the motor will run all things being well.
I must try this, I suspect it would work best on a vertical engine, in a horizontal  engine the steel wool might tend to sag a bit. By the way hows the cat?
Eric Cox21/08/2010 15:23:09
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  unfortunately the wire wool just wrapped around the shaft with no disc. consequently the wool had a tendency to remain static and not move with the shaft. I was wondering if a small piston could be made out of Fimo or similar material. Not metal as I've not got my lathe yet.
Eric Cox21/08/2010 15:24:21
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Oh yes the cat, feeling strained 
Ian S C22/08/2010 01:24:40
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A disc of thin sheet metal with a thight fitting hole could pehaps be soldered on at the cold end at least, an old food tin will do , make it 2 or 3mm less than the bore. You may get away with similar at the hot end, or if you can put a thread on it, a nut either side will take care of that.Ian S C
John Olsen22/08/2010 02:22:02
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You know I just hate to be one of those pedantic old curmudgeons who writes in to correct people, but the engine would be a Stirling engine, unless of course it is made from an alloy of 92.5% silver.
 
Given the absence of a lathe, I wonder if you might be able to come up with other ways of making a suitable displacer.  Since it does not have to be a close running fit in the cylinder, it is not a critical as turning a normal piston would be. Depends a bit what you do have in the way of hand tools, drills, taps and so on. I have seen a static model boat in which all the deck fittings were "turned" using an electric drill and a set of small files. You may be able to get hold of some suitable mesh to do it the original way. I presume the intent behind the mesh or the wire wool is for it to act as a regenerator to some degree.
 
John
 
 
Eric Cox22/08/2010 10:38:30
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"but the engine would be a Stirling engine, unless of course it is made from an alloy of 92.5% silver."
 
So what would it be if it was made from an alloy of  92.5% silver ?
John Olsen22/08/2010 11:03:04
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Very expensive.
 
But otherwise, an alloy of 92.5% silver, with the remainder usually being copper, is known as Sterling Silver. So I guess if the engine were made from that we could not quibble at calling it a Sterling engine. Doctor Bradbury-Winter did make an engine in Switzerland once out of silver, and I beleive his secretary made 400 little silver rivets for it. I don't know if it was actually Sterling silver, but very likely since pure silver is too soft to be useful for making things.
 
But if we are referring to the hot air engine devised by the Reverend Stirling, then the spelling is different. And I was probably being excessively pedantic pointing this out, but is is the gentlemans name so it is nice to get it right.
chris stephens22/08/2010 13:25:05
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Is the art of the Pun finally dead?
chriStephens 
V8Eng22/08/2010 22:10:31
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When in a pedantic mood we should take great care about our own spelling.

Edited By V8Eng on 22/08/2010 22:11:03

Ian S C23/08/2010 03:50:10
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Maybe it cost quite a bit of Sterling, thats one reason I don't build kit set engines. Mine don't look pretty but they work, and I can't just go to the model shop and buy a kit anyway.Ian S C
John Olsen23/08/2010 08:29:24
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Ah but I was only in the pedantic mood when I wrote the initial post.Or actually rather more than slightly in a punning mood, but the pun seems to have largely fallen on deaf ears.
 
Actually it is almost a law of nature that any post that raises a question of spelling will have a mistake in it.  It is also pointless worrying about the spelling of English words, since the spelling is irrational anyway, and there is actually no legal authority for correct spelling. The only authority is usage,so if we repeat the mistakes often enough in print they will become the new rule. This is already happening with the words "affect" and "effect", where a large proportion of the population have no idea which one they should be using, and although I think I know, I'm not sure I can always get it right.
 
But I do think it is worthwhile trying to get personal names right.
 
The English pound did once equate to a pound of Sterling Silver, but I think that was a bit before my time.
 
Ian S C, have you thought of writing up any of your engines and sending them to the editor? There is something to be said for projects that don't require heavy castings to be shipped around the planet. I'm a long way from the usual suppliers too.

Edited By John Olsen on 23/08/2010 08:30:23

V8Eng23/08/2010 10:54:28
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Prehaps the Editur culd orrange for a Spull Chucker to be putt oon heer.
David Clark 123/08/2010 11:17:04
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Hi There
Not at around £3,000 I can't
Be cheaper to issue everybody with a dictionary except I doubt they would use it.
Regards David
Ian S C23/08/2010 12:23:13
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I'm not too good at descriptive writing, but occasionally I come up with a few bits and pieces in threads like this one , or the stirling and hot air thread in the beginers section. Things are a bit quiet on the hot air front at the moment. The main idea of the engines that Mark1 and I build start with I think I will build(last one a Ross Yoke type motor), then hunt around for some scrap metal, ie., stainless tube from a vaccuum cleaner for a hot end, old window weights for pistons, old VHS recorder for ball races. Some old rusty scrap steel to make the frame- it had to be milled all over, then cut to size and welded together (I'm slowly teaching myself to blob weld here and there), arn't angle grinders great. I did buy some cap screws to hold it together. Ithink i paid about $NZ 30 for the cap screws and TIG welding on the stainless for the hot cap and hot cylinder, its also used about $NZ 10 of gas running it, and when I get it run in  may try and pressurise it. I will get some pictures of my motors in an album one of these days. Ian S C 
V8Eng23/08/2010 18:58:53
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Guess I'll just have to keep on using copy & paste from my WP prog.
Still that way I get a grammar check to ignore as well !
 
 

 

Edited By V8Eng on 23/08/2010 19:03:33

Gray6223/08/2010 22:29:00
1058 forum posts
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For those of you who use Internet explorer,
http://www.iespell.com/
 
for firefox, look here,
https://addons.mozilla.org/en-US/firefox/language-tools/


there are many others to support other browsers, the forum should not be relied upon to spil chok ower mistuks!!


regards


coalburner
 
 

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