Author Topic: Tiny Stirling Engine  (Read 48772 times)

Offline arnoldb

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Re: Tiny Stirling Engine
« Reply #50 on: December 07, 2010, 12:45:15 PM »
Nick, I can't offer you advise, but have been following along closely  :) - That is a really small little LTD you're busy designing and building here  :bow: :bow: - I really wish you success with it!

Kind regards, Arnol

Offline scrapman

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Re: Tiny Stirling Engine
« Reply #51 on: December 08, 2010, 06:56:29 PM »
This is an interesting build  Nick  :thumbup: what a tiny little engine :bow:,

Ray.

Offline madjackghengis

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Re: Tiny Stirling Engine
« Reply #52 on: December 09, 2010, 11:27:39 AM »
Hi Nick, good luck with the car, they always do it during the cold season it seems.  The balsa wood should turn well if at high speed and with very sharp edges.  I've got a book on LTD stirlings, and it suggests the use of styrofoam, and a hot wire to cut it.  It focuses on a coffee cup sized engine, and suggests cutting out four holes in the displacer, like one would with a cookie cutter, and filling them with stainless steel wool, as "regeneration material, absorbing the heat of the air as it passes through to the cool end, and the air absorbing the heat right back when it returns through as the displacer moves the air to the hot end.  I just thought I'd mention that although it would be a bit difficult with the size of your displacer, it would affect the efficiency of the engine overall.  :offtopic: I am truly surprised to think there isn't a key or other positive locating device on such an important part, and sensitive issue in that kind of engine.  I know also, I would never take an engine, sitting in my shop, and put it in a car without replacing a timing belt, given their propensity for shedding teeth.  That whole thing sounds like a nightmare.  On the other hand, I'm really looking forward to your success with your stirling, looking to see a video of it running.  :beer: mad jack

Offline NickG

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Re: Tiny Stirling Engine
« Reply #53 on: December 09, 2010, 11:47:00 AM »
Thanks Arnold & Ray.

Thanks for the good luck with the car Madjack, I'm at the end of my tether with those, it's a good job I've had this stirling to take my mind off it.  I did think about a regenerator but have never seen them used in an LTD, maybe it just doesn't make enough difference to warrant. I think I might try to lighten my nylon displacer and stick some very thin plastic over the holes.

I've been looking at the engine manual today and the whole thing is a nightmare-  not helped by such things as power steering pumps and air conditioning compressors - I'm in half a mind to remove them completely, make my own idler pully and tensioner.

I'm hopeful for this engine but it is extremely small!

NIck
Location: County Durham (North East England)

Offline DMIOM

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Re: Tiny Stirling Engine
« Reply #54 on: December 09, 2010, 05:46:04 PM »
.........I've been looking at the engine manual today and the whole thing is a nightmare-  not helped by such things as power steering pumps and air conditioning compressors - I'm in half a mind to remove them completely, make my own idler pully and tensioner.

I'm hopeful for this engine but it is extremely small!

NIck

going  :offtopic:  (and deliberately misreading things) if you just caught this thread at this point, I'd be wondering what power density this mini-stirling generated to drive hydraulic pumps and an air compressor! 
and/or will the project then develop equally tiny pumps and compressors ....

Dave   :coffee:
« Last Edit: December 09, 2010, 05:56:20 PM by DMIOM »

Offline NickG

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Re: Tiny Stirling Engine
« Reply #55 on: December 09, 2010, 06:28:24 PM »
Hmm, good point Dave, I hadn't read that back but it was very misleading  - apologies!

Might generate some more interest continuing on this theme though  :lol:

Nick
Location: County Durham (North East England)

Offline Bogstandard

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Re: Tiny Stirling Engine
« Reply #56 on: December 09, 2010, 07:58:22 PM »
Dave,

If you do a bit of searching on the web, the Stirling has progressed a lot further than people think.

Only a couple of weeks ago I was looking at plans from a few years ago of the stirlings that were used in the Space Shuttle program. Mainly for refrigeration systems. Again, a few years ago, Japanese students had a fully operational (and compact) motor vehicle using both solar power and very low emission and highly economical fuels driving a sterling engine for it's main source of traction.

We are rather far behind on the design of things with what we do.


Bogs


 
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Re: Tiny Stirling Engine
« Reply #57 on: December 09, 2010, 09:16:26 PM »
I was doing a little looking around for mini stirling engines on the internet and found this:

Stirling Engine Motherboard Fans Powered by Waste Chip Heat

Talk about hightech! A stirling engine powered by microchip heat and used to cool said microchip!

Offline NickG

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Re: Tiny Stirling Engine
« Reply #58 on: December 10, 2010, 04:57:01 AM »
Pretty impressive stuff Bogs!
Location: County Durham (North East England)

Offline NickG

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Re: Tiny Stirling Engine
« Reply #59 on: December 13, 2010, 06:29:06 PM »
Got a quick update tonight. I only managed 2 hours work, not pleased with the results but nevertheless it yielded 2 iffy components  :bang:

I set about making the 2 bearing uprights, one is was to be soldered (I think actually I'll glue it some how instead as I don't want to mucky up and have to clean everything) and the other bolted to aid assembly.

I started by finding some suitable brass, as luck would have it I found some 1/16" plate which is what I had designed it for - some 3/8" wide strip would have been ideal but this would be ok.

I made a bit square and marked it out, first mistake was annealing it - this made it black and difficult to mark out.



Cut the two ends off and filed to size, then put in milling machine to drill bearing hole. Mistake 2 - managed to drill off centre and using a blunt drill made a massive burr on the other side.



At least the hole was sort of square, but this is so thin I can just give the holes a bit more clearance to reduce friction if anything is binding anyway.



I could use this rod to help me hold them together while I filed one side to make the hole central again - got bored of this to be honest and it's already 20 thou undersize on width now - doesn't really matter but it's frustrating.

My marking of the radius on the top had now gone so I had to do it by eye - filing button would probably have been the order of the day here but for 1 rad on this thin bit of metal it was hardly worth it.

Here are the finished bits, even managed to drill the other hole off centre for the bolt too. A pretty poor night really, lots of scratches in it too.  :(



Final mistake was that I forgot I'd used 4mm instead of 4ba for the bolt, therefore my clearance hole isn't big enough, which means I couldn't do a trial assembly. By the looks of it I still have a burr on the top plate anyway so that'll need to go first.

I should really have paid more attention to these, because the flywheel sits between them, they are quite visible. I don't have time to go back and start re-making parts now though, I think I'd rather just prove the design if I can.

Well, that leaves me with  4 parts to make ... 2 small ends, crank and piston. So 2-3 more nights at least, hopefully I'll be finished on Friday. I will probably need to re-make or modify the displacer though which will be too heavy.

When I was eating my bacon sandwich from the canteen on Friday it occurred to me that the box may be the sort of material people were talking about:



Or alternatively, the lid I stole from the fridge could be used to seal up my nylon displacer after I have attacked it with a drill!

Nick

Location: County Durham (North East England)

Offline Stilldrillin

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Re: Tiny Stirling Engine
« Reply #60 on: December 14, 2010, 03:43:45 AM »
"Pretty poor night" , Nick? ...... I don't think so!  :scratch:

Two off, shiny, adjustable components. Plus the lessons learned during their manufacture.  :thumbup:

Also, thinking inside the box, while eating a bacon sarnie..... Who could ask for much more!   :lol:

Hope things go even better for you this eve.  :D

David D
David.

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

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

Offline NickG

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Re: Tiny Stirling Engine
« Reply #61 on: December 14, 2010, 03:54:58 AM »
David, thanks for putting a positive slant on that - think I need to do that more often when I make rubbish!  :lol:

  :lol: Yeah, if it takes bacon sarnies to inspire me, think I'll do more of that in the future!

Hope so too, approaching the home straight now.

Cheers,
Nick

Location: County Durham (North East England)

Offline madjackghengis

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Re: Tiny Stirling Engine
« Reply #62 on: December 14, 2010, 11:34:34 AM »
Now thats odd, Nick, I was having a couple of bacon sandwiches the other night, and I got a great idea of what to do with a cylinder I'd bored and finned out of some cast iron, and fitted a piston to, but didn't have exactly what kind of engine it should be part of, chosen yet.  Must be something about bacon, it's great for seasoning cast iron pans and pots as well.  Must be some special brain food in that bacon, got to eat more of it.  As David said, hardly a wasted night, just a bit of learning is all, and a couple of shiny parts to boot. :poke: mad jack

Offline NickG

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Re: Tiny Stirling Engine
« Reply #63 on: December 14, 2010, 05:13:14 PM »
Haha, it must be  - will ask the wife to add some more to shopping list as I need some inspiration right now, instead of perspiration  :lol:

 :offtopic: Earlier I had a nice phone call saying the garage had sorted my other car that conked out, they've changed a couple of parts out of good will but the real problem was the use of supermarket fuels - strange nobody else has the problem I thought. Anyway, merrily went along to pick the car up and the light on the dashboard and fault came flashing back up before I had managed to get it into 1st gear! At which point my blood reached boiling point and I politely told them to shove it! I want them to exchange the car for something else, but it remains to be seen what they'll offer me for the car they don't know how to repair. That's not my fault, I can see this being a long drawn out argument.  :bang: Meanwhile, back to my mum's volvo!

There's my excuse for not being in the garage  - getting abit late now but I may go and do an hour, might help me unwind a bit

Nick
Location: County Durham (North East England)

Offline NickG

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Re: Tiny Stirling Engine
« Reply #64 on: December 15, 2010, 06:17:39 AM »
Well, even though it was a late start, I did an hour and a half in the garage last night. Had to keep the momentum up! I started by lightening the displacer, drilled a load of holes, not right through and superglued some thin plastic over it. I don't know yet if it's enough, it's probably only 30% lighter. I was going to make a backup with some closed cell expanded polystyrene stuff from the bacon butty box, but as Bogs suggested, the glue I tried just melted it, so I'll need to get the proper stuff for the job or find some thicker material to make it from 1 lump.

After that I turned the piston from the graphite -  that stuff gets into all the little scratches in your fingers and doesn't want to wash out! I found that the bore of my power cylinder is slightly tapered so it probably won't work. I reamed it so it shouldn't be the case, really I would need to ream to next size up but I only have the odd few reamers so don't have anything to do it with now. Anyway, I've turned a piston and it seems a reasonable fit but I can't really get a feel for it until the whole thing is assembled.

Remaining parts are 2 small ends - 1/8" dia brass with a hole drilled through, a slot in 1 end and a cross hole, and the crankshaft which is the most complex component. If the solid version fails I will have to build one up and loctite together I think, might be easier anyway.

No pics, not much interesting to see but will take some tonight. Night off tonight as am off to pub for a much needed drink. Just realised it's work xmas party on Fri night too so I'll have to get my skates on on Thursday.

Nick
Location: County Durham (North East England)

Offline madjackghengis

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Re: Tiny Stirling Engine
« Reply #65 on: December 27, 2010, 01:17:48 PM »
Hi Nick, I meant to get back to you on this, I've had the same problem with tapered holes bored.  I ended up finding swarf under the back way of my carriage, and then found the carbide on the boring bar was a bit wrong angled for the material, and finally got straight boring the final cut with only a couple of thousandths, stopping the lathe with the cutter at the bottom, reversing the feed, and starting the lathe, cutting with no extra, back out of the hole.  I got down to less than half a thousandth that way, but no way to change that except do some scrapping on the headstock and the bed.  With an open ended cylinder, I hone out all the taper, and with brass, I'd use a piece of delrin or the like, to be softer than the brass, and fine carborundum in oil.  For cylinders, it's best to have a long lap, at least twice the length of the cylinder, and a short lap, about half the length.  You use the short one to remove local problems, and the long lap to even all the local work out.  On brass, I end up using polishing paste along with a block of rouge, rubbed on the lap after the paste, and it leaves a mirror polish, good for graphite.  The short and long lap method is really good when using graphite pistons, I learned it for doing hydraulic pump cylinders, and fitting new pistons in worn out ones.  It is worthwhile to make your power cylinder with a head, just so you can lap out all the taper, particularly since you've got it on a base which can hide it.  Hardwood dowel is good for laps in brass and aluminum too.  I hope you Dad relished all the work you put into his gift, and will fully appreciate it when he gets one that runs.  If you were around the corner, I'd lend a hand. :poke: mad jack

Offline NickG

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Re: Tiny Stirling Engine
« Reply #66 on: December 28, 2010, 08:45:12 AM »
Thanks for the info madjack, I just drilled and reamed my bore on this one as it was small but your comments are noted for next time I bore something properly. I don't understand why I got a tapered hole unless I had a tapered reamer, couldn't see any markings to suggest it was and I always struggle measuring reamers. I got a small set of new, common sized reamers for christmas so I should be able to achieve better results on things like this in the future. Also got a slitting saw arbor so thin slits etc should be no prob. I kept a couple of slitting saws from my horizontal mill.

Anyway, sorry I haven't been on for a while but this will be my final update on this version of the tiny stirling engine.

Here is a pic of the lightened displacer, as I said, it didn't make it that much lighter to be honest, maybe 30%. Apologies for these pics, I was just having one of those days and not a lot would go right!



Next was the piston as I said below, then the two small ends. I didn't have any 1/8" dia brass (thought I had some brazing rod but couldn't find it) so I made some square versions from some flat 1/8" brass strip. I also decided to make them a tad wider than 1/8" in the other plane so I would have more room for the slot. I selected the right drill to give a nice push fit for the pins so everything together with a pretty easy press fit. Here are pics of them assembled to rods. I was running a bit short of time by this point so sorry, I didn't get any machining pics but there wasn't much to show.



The last piece was the crankshaft. I started making this from 3/8" square brass and quickly screwed the diameter up resulting in a wobble on the flywheel before I'd even started on the journals. So that bit got scrapped, then I could only find 3/8" square steel. This was bought about 13 years ago for my 5" gauge Sweet Pea locomotive project that hardly got started. It actually cut nicer than the brass which I was pleased about.

This was a tricky component to make. I had to decide on the right order of machining operations so as to leave enough structural integrity so that it wouldn't bend.

The first job was to centre it in the 4 jaw. That wasn't too difficult as I found out 3/8" was the smallest size my 4 jaw would go down to - this became a problem later. I faced each end to overall length then turned the longer plain diameter for the flywheel and the 1/8" spigot for the bearing. Turned it around and did the same on the other end so each end was concentric (within the accuracy of my 3 jaw - good enough).

That's when I was going to put it back in the 4 jaw to offset turn the journals but of course I couldn't, the 4 jaw was too big, when I tried to get the offset the jaws just clash into each other.

So I decided on a fool proof way of getting the 1/8" offset to give me 1/4" stroke. I just put a bit of nylon in the 3 jaw, offset by 1/8" with a bit of packing under 1 jaw, centre drilled and drilled a hole for a tight fit on the plain diameter, then put a saw cut through to the hole along the length of the offset bush. I then clamped the crankshaft in the bush in the 3jaw. I was struggling to get it to grip the shaft but when I did, I took too big a cut and it mangled the nylon and pulled the shaft out - luckily or miraculously no damage. So I decided to make an alloy split bush instead by the same method. This gripped much better.

I turned the journal furthest away from the chuck first, then the one nearer in, as I said so it still had enough strength. This worked pretty well except I possibly got a little frightened as it was approaching 1/16" diameter and stopped a little large.

When I took the crankshaft out, it had turned out well except I don't think it had achieved the 1/8" offset I required. How could this happen? I just assumed if I put 1/8" packing under 1 jaw that would do the trick, or did I need to work some geometry out? I've never even thought about it to be honest!



This was on Christmas eve or the night before I think so I didn't have time to make a new one, I just thought I'd have to try it. The effect this would have is to leave dead space at the top and bottom of the displacer though - not good.

I thinkit was on christmas eve that I assembled the engine. Here are the assembly pics.









I forgot to mention, the other issue on the crankshaft was, I got carried away and forgot to make the journals the correct width. I thought ah, it'll be near enough jsut being the width of the parting tool - that way I only had to do 1 plunge for each. But it wasn't quite - When I assembled, one of the bearing uprights was to be super glued onto the top plate but to get it free running, I had to put a couple of shims under it to prevent metal to metal contact with the crankshaft and one of the rods - luckily I had allowed enough clearance on the length of the crank main bearings to allow this.

The other bit I found difficult was putting the rods onto the journals - these were the ones that had slits in the big ends to bend out, over journal and back in. With hindsight, I think I needed bigger slits. The plan was to bend them back with the long nosed pliers but I couldn't get in with those. I might have been able to do it resting on something and  acouple of taps with a hammer and thin piece of steel. Not a great way of attaching the big ends really I don't think. May have been better building a crankshaft up of 3 or 4 bits but I thought I'd try to be clever and make from one piece!

The engine seemed very free running, I tried it on top of a flat bit on the heated towel rail and couldn't really get a peep out of it. It span over faster (10 or 15 revolutions) in the direction of running and only 4 or 5 in the opposite direction but nowhere near running I don't think.

Tried holding it over a tea light too and that was no different.

I think there are a few reasons it didn't run. The first, was the crank didn't have a long enough stroke leaving too much dead space in the system. Secondly, the fit on the displacer rod and piston could have been better. Thirdly, friction was possibly still too high even though I thought it was free running enough. The fourth could be the weight of the displacer, although the assembly seemed fairly balanced to me, it didn't seem to settle in any particular place. It had the weight of the piston and pin etc on the other side. Maybe the flywheel was also too heavy. If I make another, I will address all of these issues and hopefully have a runner.

I could provide drawings but I don't think anybody would want to risk spending the time and effort making something that might not work so I'll wait until I've built a working version.

My dad seemed happy with his present. Put a copy of the general assembly drawing wrapped up with it so he knew I'd design and built it with the intention of giving it to him for Christmas. I was gutted to have to give him a non working model though, if I do make a working version his will be swapped for it!

Nick

Location: County Durham (North East England)

Offline raynerd

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Re: Tiny Stirling Engine
« Reply #67 on: December 28, 2010, 12:24:08 PM »
Nick, looks great and even as a non-runner, it is a smashing model of a LTD stirling. I`m sure your dad won`t want to swap it and will appreciate the time you spent in making and drawing the plans up. It is nice giving something that you made, my dad really liked his puzzle I made him - I think Dads appreciate the time involved!

Just curious, did you do a water test and submerge it to see where the leaks were?

Offline NickG

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Re: Tiny Stirling Engine
« Reply #68 on: December 28, 2010, 01:41:28 PM »
Cheers Chris, glad your dad liked the puzzle. I think they do appreciate it but I still would have felt 100 times better if I could have showed him it running! I literally didn't have time to do any trouble shooting so didn't even do leak test but if I was a betting man I would put money on around the displacer rod and probably power piston. I think my seal between the tube and top and bottom plates was good as they were sort of a snap on fit and I glued them on too. When I first made the bits I blew into the holes unglued and there was no leak on the bottom, very slight on top which I assumed would be easy to stop with glue. I might do some trials with offset turning and what sizes I need to make the big ends for them to snap over the crank journals or think of a different method as wasn't happy with that.

Nick
Location: County Durham (North East England)

Offline Bogstandard

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Re: Tiny Stirling Engine
« Reply #69 on: December 28, 2010, 05:47:59 PM »
Nick,

Just a couple of pointers.

The first is that even though it doesn't run, you have learned a lot from your mistakes. Mistakes get remembered a lot longer and easier than successes, so you won't do them again.

The other is concerning reamers.

As far as we are concerned, you could basically class them as two types, hand reamers (including adjustables), and machine reamers. There are loads of other types, but for our use, just the two.

Hand reamers have a square on the drive end that fit a normal type of tap wrench, and machine reamers will be either straight shank for fitting into a drill chuck or morse taper.

The major difference (in this easy to understand text) is that hand reamers have a long lead in taper, up to 1/3rd of the length of the cutting edge in some cases, and machine reamers normally usually have only a very small lead in taper.

Where this is leading, is that you said you ended up with a tapered bore after using a reamer. Two causes for that if they are hand reamers, the first is that you used the wrong technique for cutting and you made the beginning of the hole larger because you wobbled about a bit, or the usual cause, you didn't penetrate with the reamer all the way thru, so didn't reach the parallel part of the cutting flutes, only the tapered lead in area. It is for that reason you can't use normal hand reamers in blind holes, the bottom of the hole will always end up tapered.

You don't usually get this problem with machine reamers, because they are parallel for almost all their length, but you can still end up with tapered bores, especially if your tailstock isn't exactly central.
A floating reamer holder solves most of those problems. A project for me that isn't very far off.

I hope this helps

John
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Location - Crewe, Cheshire

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Offline cidrontmg

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Re: Tiny Stirling Engine
« Reply #70 on: December 28, 2010, 06:52:10 PM »
Hi Nick, I have been reading the whole thread once again, and figuring out what to suggest. But havenīt come up with anything obvious or show stopping. Itīs difficult to make remote diagnoses  :doh:
That displacer seems to me rather heavy. Styrofoam, polyurethane, balsa, something a lot lighter would probably be better. The displacer rod also seems to be touchy. Itīs prone to leaking, and that will make quite a difference. The power piston leaking slightly wonīt be nearly as harmful.
The all-important thing is, it must be free-running. Reducing friction is far more important than reducing leaks. I guess the bearings are OK, but if you have any oil/grease(!) in them, you should wash it all away. With my engines, I rotate the flywheel back and forth in +/- 10o steps, through the whole circle, and listen and feel if thereīs any scratchy noises or stiffness anywhere. And do my best to find the causes, and reduce them as much as possible. If I give the flywheel a flick with my finger, the engines make some 8-10 rotations, accompanied by a "swoosh-swoosh" noise, coming mostly from around the displacer rod. I cannot make it completely airtight and still make the engine run. But itīs not a LOUD noise, barely audible, and it is more when the displacer is moving towards the hot end.
The engine might need a bigger heat difference. If you cooled the top cover, by putting some ice (snow... I guess that could be arranged... :) ) on it, it might show some vital signs...
Other than that, and without seeing/feeling it, quite hard to suggest anything. Wish you the best of luck with it!
 :wave:
Olli
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Offline NickG

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Re: Tiny Stirling Engine
« Reply #71 on: December 29, 2010, 03:14:46 AM »
John, many thanks fir the reply. Now that you've explained about reamers I think I've seen you explain in another post but I'd forgotten. This could very well be the case as it was a hand reamer I used, I don't think I wound it all the way through and the cover is relatively thick. My new reamers are also the hand variety but look a bit longer so hopefully will have a longer parallel section. I'll be sure to wind right through and use it as a floating reamer supported by tailstock if that's a better technique. Olli, thanks for the trouble shooting techniques, and the displacer material will definitely be as suggested by a number of people this foam next time. I will also try to lighten all of the rotating / reciprocating components. Cheers guys,
Nick
Location: County Durham (North East England)

Offline madjackghengis

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Re: Tiny Stirling Engine
« Reply #72 on: December 29, 2010, 12:29:58 PM »
Hi Nick, as John said, reamers are fickle things, and while one seldom finds a less than straight machine reamer, if of decent quality, one does get by occasionally.  Most of the time, a machine reamer reams taper because it is held too rigidly, and for instance, my tailstock dangles about two or three thousandths, from sixty odd years of wear, so a proper reamer holder would improve their performance much.  With regard to the eighth in shim in the three jaw, you effectively only moved the radius a sixteenth, this was the error I made in turning my cam in my Duclos flame sucker, twenty years ago, and prevented it from ever running until this year.  Were I you, I would look for a piece of balsa wood to make the displacer out of, as that seems to be generally available in hobby stores, and it has been proven out many times.  My wife hates it, but I have no problem digging in the "green boxes" and rescuing someone else's trash, if I see machine parts available, or scrap metal for stock.  I only buy metal when I have to, but I've got tons of iron and steel from years of a machine shop, and quite a few hundred pounds of aluminum of various sorts.  One should never let a printer or computer go in the bin without being disassembled, and all the useful parts kept.  You might need to practice more scrounging :poke:, if you're going to build engines.  None the less, it is nice looking, and I'm sure you'll get it all sorted out soon, after the holiday rush.  :bugeye: :thumbup: mad jack

Offline NickG

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Re: Tiny Stirling Engine
« Reply #73 on: December 29, 2010, 12:48:10 PM »
Thanks Madjack,

I think I will have to wait until after the holiday rush! More car trouble and it's just becoming so annoying now. I managed to get the dealership to do a straight swap for the citroen that had all the issues with it for a Vauxhall Vectra SRi. Despite the dealership being a bunch of incompetent ***** I thought I'd got a good deal out of them in the end. I picked the new car up on Christmas eve, it was a year newer than the other and a petrol this time - 3 days later the engine management light was on on the dashboard, had a friend plug it into the vauxhall diagnostic (thanks to him as just doing that normally costs Ģ65 + vat!) and it says there's a fault with the 'cam phasing mechanism' - another engine with daft variable valve timing ... why does everything have to be so complex these days?! So I'll no doubt have more trouble getting that repaired and getting the dealership to pay for it, but they better do, only had the car 4 days!

I have sketched the thing with the 1/8" packing to get the right offset and I still don't understand why it wouldn't give me the right offset, surely you are just moving it 1/8" off it's original centreline by doing that, I can see that if you put it under 2 jaws it wouldn't move as much but just under the 1, shouldn't that have worked?

Nick
Location: County Durham (North East England)

Offline andyf

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Re: Tiny Stirling Engine
« Reply #74 on: December 29, 2010, 02:03:47 PM »
I think you said you were putting 1/8" packing under one jaw of a 3-jaw chuck. With a 3-jaw, you only get an offset which is 2/3 the thickness of the packing, so 1/8" packing offsets by 1/12". If you want 1/8" offset, you need 3/16" packing.

It took me a while to get my head round it  :scratch: :scratch:
There's an explanation of a sort three-quarters way down this page:
http://homemetalshopclub.org/news/aug03/aug03.html

Andy



« Last Edit: December 29, 2010, 02:22:42 PM by andyf »
Sale, Cheshire
I've cut the end off it twice, but it's still too short