Stirling Engine : Laura

My wife just bought a potato peeler- this has a handle ,stainless steel tube 19mm dia. and about 0.5mm thick, 160mm long. Might be worth looking out for, cost about £3. IanSC- you mentioned making teflon piston rings a while back, How much did you allow for piston clearance and how did you make the joint ?

The same as my ''stainless steel'' tubing from the bathroom section of the hardware store : definitely not stainless steel all the way through.

No luck with the stainless steel piston : very disappointing as I was sure that would work. It seems to get even hotter than the aluminium piston. I certainly burnt myself on it after taking it out ! So then I tried a new aluminium piston with the front edges slightly rounded and this did run for a full minute...but only once !

My flame eater kit has arrived from Bengs ; I may make a start on machining the two cast iron flywheels of that kit while I give this one a rest for a while. The only thing that has not been tried on this engine is the stainless steel D cylinder.

What was I thinking ? I spent the whole afternoon making up a stainless steel D cylinder but when I silver soldered it to the brass collar I had it resting on a couple of galvanised steel plates to keep it all level. I did not think the solder would take to the plates but it did ; I guess some of the flux dribbled through. If I had wanted  it to stick together then I bet it would not have ! Unless anybody has a good suggestion then this one will end up in the bin.

Edited By Brian John on 15/05/2016 11:07:22

Edited By Brian John on 15/05/2016 11:29:55

Just heat the galvo plates up and pull them off when the solder gives way. Wrap a wet rag, or a potato, around the body of the displacer cyl so the solder on the flange there does not get as hot as the solder on the galvo plates.

Yes, I was thinking about that while having dinner. I have not had much luck with remelting silver solder in the past but in this case I doubt that there is very much solder holding the plates to the work piece. It is worth a shot.

A potato ?

jamming whatever you want to keep cool into a potato is a classic trick for it to act as a heat sink. Of course a mangelwurzel, turnip, khol rabi or perhaps a parsnip would all show individuality in use

Whatever the reasoning, it did not work. I heated the plates up until they were red hot but they will not budge. Typical...just when you DO want the solder to fail !

Edited By Brian John on 15/05/2016 15:47:45

Hi Brian,

I would put the cylinder in the lath and machine the offending bits off.

Hope this helps.

Peter.

Unfortunately that brass cap on the end of the shaft is slightly larger than the stainless steel shaft which prevents me mounting it in the lathe chuck. It would need to be clamped around the shaft. Is there a way to do that by perhaps clamping the shaft with some mounting blocks ?

I am getting out the angle grinder today to clean up some large cast iron fly wheel castings. I might have a look at getting a thin cutting wheel in there somehow.

Edited By Brian John on 16/05/2016 02:22:28

I gave up trying to salavage that hot cap ; it was not made of real stainless steel anyway. Today I have made a new one from proper stainless steel purchased from the boat supply store as per Hopper's suggestion. The brass end cap is different design on this one. Nothing is soldered yet. I might even use JB WELD to see how it goes and if it does work then I can silver solder it later. I did manage to save the brass collar from the old hot cap ; that may be useful in the future. I bored it out using the boring bar.

The new hot cap has been soldered up today. I was careful to give the bottom a light coating of machine oil so that nothing would stick if the solder did flow all the way through ; I also coated the jaws of the vice with oil. But I judged the amount of solder correctly this time so there was no problem. It certainly looks the part but does it work ? I have to go out now and I will give it a try later.

I did have some problems fitting the collar to the D cylinder after soldering and I had to polish the collar with some 400 grit in the lathe to get it to fit. What happened there ? It was an easy (not tight ) fit before soldering.

Edited By Brian John on 19/05/2016 10:02:42

G'day Brian. A useful trick to prevent silver solder flowing to unwanted areas is to use a soft graphite pencil.

This site describes a few useful techniques **LINK**

* Danny M *

Thanks Danny, there is some useful information there.

It will not run ! I really thought it would this time but I was closer last week with the ''fake'' stainless steel tube. The real stainless steel tube is not working for me. I have no friction... I have a sealed system (I can feel the suction) ...but I do not have a functioning Stirling engine. I am now out of ideas.

I might put this aside for a few weeks and get on with the flame eater engine. The face plate and clamps are ready to machine the flywheels.

Edited By Brian John on 19/05/2016 15:25:43

I would try taking that brass sleeve off the hot end of the displacer cylinder. Brass is an excellent conductor of heat, so it is doing a good job of transferring heat from the flame on the end of the cylinder halfway up the length of the cylinider, which defeats the object of using a stainless cylinder to minimize heat conduction. You might try instead a short brass cap that basically covers the end of the cylinder and extends only , say, 6mm down the cylinder. This will hold the heat at the very end of the cylinder rahter than spreading it along toward the cool end.

Also the brass flange on the displacer cylinder is going to absorb a lot of heat and then allow it to flow back into the air right there next to the cool end. But a stainless flange might be a bit tough to machine on your little lathe. However, even a mild steel flange will have more suitable thermal properties for this application than brass..

I might be able to mount the collar in the lathe chuck, drill a shallow centre hole in the cap so that I can turn between centres and then using a LH cutting tool reduce the brass cap that way. I will have a look at that tomorrow. I knew I should have used JB WELD on the collar : it was only a last minute decision to solder it !

I do not think I could make a mild steel collar on this lathe. Turning it would not be a problem but drilling and parting off would be out of the question. I struggle doing this with 30mm diameter brass.

I bought some exhaust manifold gasket material a few days ago but I was unable to cut it ; it is very tough stuff. I was bashing away with a set of centre punches and not getting anywhere. I think I should look at this again. It would be placed between the brass collar the D cylinder to prevent heat transfer. I could cut the outer shape with tin snips and perhaps drill out the centre hole with a step drill...maybe ?

Edited By Ian S C on 21/05/2016 09:45:08

I reduced the cap down to 6mm as per Hopper's suggestion. I will try it out later. Photo 1 shows it being cut with the LH cutting tool and photo 2 is after polishing

I did not get time to try drilling the exhaust gasket today. I want to use the exhaust gasket to prevent heat transfer to the D cylinder...or at least slow it down a bit.

Edited By Brian John on 21/05/2016 10:02:51

Edited By Brian John on 21/05/2016 10:04:10