Stirling Engine : Laura

[roy entwistleParticipant @royentwistle24699]

Brian John Why bore it make a mandrel and reduce the outside Use the inner bore as is as long as it's smooth

[HowiParticipant @howi]

Sounds like it is close, but if the displacer cylinder is not stainless you will get too much heat at the cold end. The air needs to go from hot to cold to hot etc, it is the temperature differential that drives a Stirling.

[Brian JohnParticipant @brianjohn93961]

I bought some exhaust manifold gasket material today but that idea went nowhere. How do you cut this stuff ! I hammered away it it with hole punch for 10 minutes and got nowhere. Even a sharp scalpel blade is useless. Anyway I gave up that idea and moved on to making a stainless steel D piston from the 12.8mm OD stainless steel tube.

Initially I was going to make the two ends to the piston from brass and then silver solder them in place but then I had this idea (how many times do we hear that !). I have put an M3 thread in the'' hot'' end , the piston rod is threaded so that it screws into this after passing all the way through the brass fitting at the ''cold'' end. That brass bush is held in place with an M3 grub screw. Looks good but will it work…I will give it a go later tonight.

The stainless steel is tough stuff and I comepletely destroyed my M2 spotting drill. Ideally the tube  would have a thinner wall : 1mm would be good but for now I have stuck with the original 2mm wall. I am not sure how this stuff would go with a boring bar. I might give that a go tomorrow if I make another piston. I was able to clean up the ends in the lathe with no problem so perhaps machining it is easier than drilling into it. Even tapping it was no problem with plenty of tap magic being used.

Edited By Brian John on 14/05/2016 08:22:39

Edited By Brian John on 14/05/2016 08:25:10

[AjohnwParticipant @ajohnw51620]

There are all sorts of stainless steels Brian. When Ian uses a tube out of a nicad battery he will be using a ductile grade which will be more or less the same as a free machining grade. These are much easier to machine than the "true" stainless steels. It's pretty easy to tell the difference with a magnet. The easier to handle grades are slightly magnetic. Treated with a bit of respect you shouldn't have much trouble turning them.

John

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[Ian S CParticipant @iansc]

The case from the NiCad is just used "as is". I needed some tube for a job the other day, a bit of towel rail tube was the right size, I needed about an inch off it, so I decided to use the parting tool as it was all set up, went in about .010" and the shiney outer surface stopped while the rest kept turning, there was a chrome plated brass tube fitted over a steel tube. All is not always what it seems.

Ian S C

[Roger Provins 2Participant @rogerprovins2]

I caught out much the same way. Bought a bundle of what I thought were 1/4" brass rods only to find that they were steel with a thin brass outer shell and brass finials.

Rog

[Gordon WParticipant @gordonw]

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 ?

[Brian JohnParticipant @brianjohn93961]

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

[Brian JohnParticipant @brianjohn93961]

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.

[Brian JohnParticipant @brianjohn93961]

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

[HopperParticipant @hopper]

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.

[Brian JohnParticipant @brianjohn93961]

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 ?

[pgk pgkParticipant @pgkpgk17461]

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

[Brian JohnParticipant @brianjohn93961]

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

[Peter TuckerParticipant @petertucker86088]

Hi Brian,

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

Hope this helps.

Peter.

[Brian JohnParticipant @brianjohn93961]

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

[Brian JohnParticipant @brianjohn93961]

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.

[Brian JohnParticipant @brianjohn93961]

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

[Danny M2ZParticipant @dannym2z]

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 *

[Brian JohnParticipant @brianjohn93961]

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

[Ian S CParticipant @iansc]

You may have to heat it a wee bit longer to get the heat into the motor, the hot end looks quite thick, it might take a minute or two. Don’t worry. it will go,you just have to sware at these things the right way.
Ian S C

[HopperParticipant @hopper]

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..

[Brian JohnParticipant @brianjohn93961]

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 ?

[Ian S CParticipant @iansc]

The thickest gaskets I use are made of thin gasket paper (about .25 mm), exhaust gasket material is ok for exhausts.
I must try boring out a hot cap, or similar on my Super Adept, when I manage something on that, I reckon it can be done on any mini lathe, it will take a .25 mm cut from a bit of 1″ diameter 303 stainless steel bar.
Ian S C

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

[Brian JohnParticipant @brianjohn93961]

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

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