Stirling Engine : Laura

[HopperParticipant @hopper]

… on my Super Adept, when I manage something on that, I reckon it can be done on any mini lathe, …

[Brian JohnParticipant @brianjohn93961]

Still no luck ! I really thought that might work today. I will try the exhaust gasket next and if that does not work then I think I will go back to using that thin-walled fake ''stainless'' steel tube I was using before. I was very close to getting that to run.

[Ian S CParticipant @iansc]

Even if the “fake” SS is not actually SS (it can still be SS and be magnetically atracted), and it’s mild steel, thats ok, it wont last so long, but it is ok.
If you get to bigger motors the pipe for the extension on a domestic vaccuum cleaner is useful, some of those are chrome plated mild steel, others SS, I’v used both.
Ian S C

[HopperParticipant @hopper]

…then I think I will go back to using that thin-walled fake ''stainless'' steel tube I was using before. I was very close to getting that to run.

Why not have a go at boring out the inside diameter of the new cylinder? It looks like you might have to make a split collet of some sort if you can't just reverse it in the regular jaws. Did you ever get your fixed steady? Might be able to hold the cylinder by the brass hot cap in the chuck jaws and use the steady to support the other end while you bore it out.

Use a boring bar the largest possible diameter that will fit inside the existing bore. It might chatter a bit on your small lathe, but that is not important for a non-bearing surface like this. And you can clean it up with your homemade brake cylinder hone. You can make a simple boring bar out of a piece of round steel bar with a hold drilled in the end to take a piece of HSS and a tapped hole for a clamping screw. That way, you can make a bar that is a good solid size.

 

 

Edited By Hopper on 23/05/2016 03:37:56

[Brian JohnParticipant @brianjohn93961]

With the small boring bar I have now, it flexes too much to machine a long stainless steel tube like this. As you have said , I will need a larger boring bar for this job. I passed on the fixed steady as I did not think I would ever use it. I already have one hot cap already made up using the thin walled tube. I would like to get this going before I start machining the inside of the thicker tube.

It could be that this engine just will not run with a hot cap due to its small size. Perhaps that is the reason that Bengs designed it with a glass tube. But I will keep experimenting for now ; it is all useful experience finding out what works and what doesn't.

[Ian S CParticipant @iansc]

The main reason for glass hot caps is so that you can see the "works", some are made with a glass displacer inside the glass hot cap.`  Ian S C

Edited By Ian S C on 23/05/2016 14:57:21

[Brian JohnParticipant @brianjohn93961]

I think it is also to do with glass being a poor conductor of heat. On the glass cap engine, it takes ages for the D cylinder to get too hot to touch but on the stainless steel hot cap engine, it only takes a few minutes.

[Brian JohnParticipant @brianjohn93961]

I gave up on trying to get this engine to work with a stainless steel D cylinder and I made another brass and glass D cylinder as per the original plans. It does not work ! Now I am very puzzled. I have built one of these before and this one is now exactly the same. It looks like the problems I was having before were not caused by using a stainless steel D cylinder after all.

I have got pressure : I can feel it when I take the cylinder cover off the work cylinder and put my thumb over it. The whole engine is very free wheeling. I am not sure what to do to fix this but there is still a chance that this engine may work with a stainless steel D cylinder if I can work out what the problem is.

[Ian S CParticipant @iansc]

Brian, I assume that the SS displacer is hollow, does it leak? To find out take it out of the motor, and put it in a pot of hot water, if it leaks it will blow bubbles, this must be sealed. Ian S C

[Brian JohnParticipant @brianjohn93961]

Ian, it is an aluminium displacer piston on both the glass and stainless steel D cylinders. The shape is different as the displacer for the glass cylinder has a bullet shaped end.

[Ian S CParticipant @iansc]

I that case I presume it is the original solid form. You are sure there are no leaks else where, and friction is at it's minimum, if the rod guide on the displacer. Wipe out the power cylinder and piston with tissue/loo paper, kitchen paper towel, re lub if required. Ian S C

[Brian JohnParticipant @brianjohn93961]

Ha…found it ! Where the work cylinder joins the cylinder frames. I inspected all mating surfaces and polished the ones that I could. But this one looked like it might be suspect and could not be polished so I fitted a gasket to it and off it went…just like that. So now I can try it with the stainless steel D cylinder and I am sure it will work.

I should have built it with the glass D cylinder in the first place to make sure the whole system was sealed and working.

[Ian S CParticipant @iansc]

They usually work, sometimes they just take a bit more thought, and fiddling around. Ian S C

[Brian JohnParticipant @brianjohn93961]

I managed to get this engine to work with the stainless steel cylinder last night : it ran for about 5 minutes before stopping. I think I just need to tweak the D piston diameter and it should run for much longer.

I was making another D piston today out of aluminium and I broke the tips of three 1mm (size of drill tip) centre drills when trying to mark and drill the centre hole for the piston rod. What on earth is going on here ? Did I get a bad batch of centre drills from China ? I have never broken a centre drill before.

Is the size of a centre drill denoted by the drill tip or the shank of the body ?

Edited By Brian John on 17/06/2016 09:05:53

[JasonBModerator @jasonb]

Brian, try a spotting drill for starting holes and keep the centre drills for when you actually need to put the tailstock into the hole for support. A 3mm and a 5mm one will do all youi are ever likely to need.

There are various BS standard sizes of ctr drill but you can get different tip diameters for a set shank size – the BS number refers to shank size.

[Brian JohnParticipant @brianjohn93961]

I would have thought a spotting drill would be more likely to break than a centre drill which is the main reason I have been using centre drills for this ?

[Brian JohnParticipant @brianjohn93961]

Finally … success at last : the engine ran for the full 20 minutes of the meths burner with no problems. I am still to fit the whole thing to a larger wooden base with brass handles but here it is anyway. At least now I know that it does work using a hot cap so I can dispense with the glass tubes.

 

NOTE : this is the thinner ''fake'' stainless steel. ID of cylinder is 14.5mm and the diameter of the piston is 13.2mm.

Edited By Brian John on 17/06/2016 14:23:52

Edited By Brian John on 17/06/2016 14:26:06

Edited By JasonB on 17/06/2016 14:26:42

[JasonBModerator @jasonb]

The spotting drill does not have the small dia end so nothing to snap off.

 

Looks good running

Edited By JasonB on 17/06/2016 14:27:05

[Brian JohnParticipant @brianjohn93961]

So here it is in its final configuration on a wooden base. I spent some time this afternoon re-machining that problem surface between the base of the work cylinder and the cylinder frames. I used the sharpest tool I could find and I even made a wooden jig so I could give it a polish with some 1500 grit. No luck at all…it needs that gasket to run so I have left it at that. I am quite puzzled as the surface looked smooth enough to me.

Is there any reason the meths burner should be made from brass ? I might try building one from aluminium as it seems like a waste of good brass.

**LINK**

 

Edited By Brian John on 18/06/2016 10:06:27

[pgk pgkParticipant @pgkpgk17461]

Posted by Brian John on 18/06/2016 10:04:29:

…

Is there any reason the meths burner should be made from brass ? I might try building one from aluminium as it seems like a waste of good brass.

..

As a kid i made them out of old ink bottles and even tobacco tins. Some pretty dodgy examples survived if there wasn't too much 'back heat' . Ally instead of brass should be fine

However I suggest you don't try and repeat my experiment using one burner to boil another meths container for a pressure vapour system. That could have ended in tears if my dad hadn't pulled his idiot 11yr old out of a garage full of meths vapour……….

[Ian S CParticipant @iansc]

My little bohm HB7-AO2 has an aluminium burner, don't see why you can't have one too. Ian S C

[Brian JohnParticipant @brianjohn93961]

I took the other Stirling engine fitted with the glass tube and replaced it with a thick stainless steel hot cap. It will run for about 5 minutes then stops. I am not sure why it stops but it does get much hotter in a much shorter time than the thin walled hot cap. I did try to reduce the wall thickness of the tubing but my lathe and boring bar are not up to it. The bar just flexes away. This thicker stainless steel is VERY tough stuff ; it is marine grade stainless steel. I used the parting tool to reduce the length of a piece of it and I have never had so much trouble. It is only 1.5 mm thick but it took forever to cut through it even using cutting fluid.

I know the engine works with the thin walled hot cap which is probably not stainless steel. It looks like I will have to stick with that unless somebody has some other ideas.

[HopperParticipant @hopper]

Brian the biggest bugbear when machining "real" stainless is the material work hardens if you let the tool rub on it, usually by taking light cuts. You have to have good sharp tooling and "keep the work up to it". It might help with boring the tube if you make a mild steel sleeve to go over the outside of it and then hold that in the chuck. This stops the thin tube wall from flexing away from the boring bar tip. And use the fattest boring bar you can fit in the hole to minimize flex there. Keep the rpm lower than normal too.

[Brian JohnParticipant @brianjohn93961]

I only have the one small boring bar at the moment. I have been thinking of buying something larger and more substantial with less flex so now is the time.

It would also be great I could buy some 15mm OD stainless steel with a 1mm wall. I see it is available in the UK so somebody must have it in Australia.

[Brian JohnParticipant @brianjohn93961]

I wonder if a 13mm stub drill passed through the steel tubing would achieve the desired result ?

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