Hi Everyone,
I've have sourced some steel tubing with an inner diameter of 33mm. I'm having trouble thinking of what use as a piston. The biggest problem I have (so far) is I don't have a lathe. I'm a little lost on what to do.
End point I'm going for (I know thus may not work) is a much larger version of a syringe alpha stirling engine. So there's no fly wheel, just a metal U-tube, hot area, regenerator (fine metal wool) and a cold area. I just need the pistons. I haven't yet gone to the supermarket to measure all their cans but may do tomorrow
I live in Chippenham, Wiltshire, UK if anyone wants to join up to build?
Is the tube you intend to use actually as round as it needs to be? most round steel tube isn't very round, we're only talking a few 10ths of a mm but that'll make a big difference, the fits required for a good enough seal are in the order of 100ths of a mm (or ideally less) so you may run into problems. using o-rings (or other flexible seal) may reduce this problem but the friction is going to be a major factor, and will probably result in faliure. An adjustable reamer might help, but the tube will flex as you cut so will probably not end-up as round as you'd like. and a large enough reamer won't be cheap or easy to get.
A graphite piston is a possibility, if you can get a slug of it big enough, and somehow rotate that slug, you may be able to "turn" it down to size with a bit of abrasive paper stuck to a board (or even 2 boards with a hinge in the middle to work 2 sides at once)
Do you own a drill-press? there's a LOT that can be done with a simple drill-press and some care, but you'll be hard pushed to get the precision required. I did manage to make a working steam engine, with nothing more than a drill-press and hand tools, but it also took me about a month of evenings to actually get the thing made and running!
Another thought, it may be possible to make an aluminium lap from a piece of round stock that's close to the size you need, split this at 4 points then drive a screw down the center (a long woodscrew would work in a pinch) it may take some time, but you may then be able to lap it to the correct size and reasonably parallel. that can then be used to lap your steel cylinder with silicon carbide. it all depends on your level of patience, and accurate measurement.
there are some alternative sources for piston/cylinder materials, Automotive brake/clutch cylinders are a possibility, and telescopic dampers do have lovely bits of chromed steel in them (though even HGV shocks don't have much more than 20-25mm rods) it may be worth looking out for a bottle-jack at the next car-boot you frequent as although o-ring sealed, the clearances in hydraulic cylinders are pretty tight to start with in order to stop the seals from squirting out of places they shouldn'tm, and with a little imagination, you may be able to find a way to seal them with minimal friction.
Side note; as an apprentice, I watched an old-hand make an o-ring from PTFE tape with nothing but his bare hands, a metal rod to roll it on, and about half an hour of patient work. it got us out of trouble long enough for a real o-ring to arrive!
You could grease up the cylinder tubing, place it on a flat surface and pour a epoxy piston. I have a epoxy piston in one of my engines and it works great! Before it set up I put a small piece of balsa wood in the middle which I picked out, after it set up, to make a hollow area for the connecting rod.
Ohh, that's a good one! maybe carving a positive conrod pocket out of wax, then just drop it in hot water after the epoxy has hardened to remove the wax, you could get pretty fancy with that technique if you really wanted to.
I've tried a few things but not working. So am keeping my eyes out for an old jack I can repurpose.
I did try a water piston so made a fluidyne engine which was surprisingly easy. So the project has moved on slightly and now playing around with different coils of copper wire to see if I can generate a couple of volts.
Speed of a fluidyne engine is an issue, I can see why they are not used to generate energy!
Oh well keeps me out of trouble.
Thank you all once again for your ideas, suggestions and help.
Kind regards
