Advice for ratios

[Ante]

Hello people
here I am again..

After lots of searching I found material for cylinder and displacer chamber.
cylinder is nice copper pipe ID 2cm
and for displacer chamber i found steel spray can.

Problem is that the spray can has diameter 6.5cm and high 12.5cm it is not ratio 1/3
So my question is what are your suggestions for:
stroke of working piston
stroke/height of displacer

my opinion is that maximal stroke of working piston for diameter 2cm is about 5cm
if I try to keep all ratios, stroke of working piston will be to long.

Thanks in advance

[Longboy]

Your solution is to shorten the displacer stroke with unmatched cyl. diameters. The diameter of the displacer cylinder is three times the copper pipe diameter. Equal air exchange of unheated air volume is controled by how deep you plung the displacer and power piston into its their bores so set the strokes for a more matching volume of air displacement.

[Ian S C]

Copper is not ideal for a cylinder, because what ever you use for a piston it will have a relitively high coefficient of friction. Cast iron, with either a cast iron or steel piston is best, followed by steel with a cast iron, bronze or brass piston, a brass or bronze cylinder with a steel or even stainless piston. Note that apart from cast iron, you should not run like metals together. I see that some of the tin can motors are built with copper cylinders, and JB Weld pistons, so it will work, but one should work to optimise the performance what ever motor you make.
I would suggest that a stroke of between 1.5 and 2 cm for a power piston would be better than 5 cm, and I would be looking for a skinnier can for the displacer cylinder, 6.5 cm is a big can, just be sure that the one you get is steel.
The ratio between the two cylinders should be about 1.5: 1, and the length of the displacer should be 3 x the diameter. ian S C

[Ante]

Jan thank you for advices
I did not find steel can of smaller diameter high enough, so I will try with this can D=6.5cm , but smaller stroke of displacer.
I expect volume ratios Vdisp/Vcil about 8.
about material for cylinder, because I don't have lathe only way to make nice piston-cylinder is copper pipe and epoxy, after little experimenting I am able to get very nice fit.

p.s. i have some pipes of vacuum cleaner for displacer chamber but I don't know how to close hot side. Is it propane butane burner powerful enough for silver soldering? if it is not what is cheapest solution.

Thanks in advance

Ante

[Ian S C]

With a larger size torch you should be able to silver solder, You would be better to braze, but your getting to where you need oxy/ gas, oxy acetylene.Another way to get enough heat, I have a carbon arc torch for my stick welder. The ideal way is to weld the end on. I'v done that with stainless steel, well I got a mate to do it, it was TIG welded. With plain steel (ex vacuum cleaner), I welded a bit of 1/8" thick steel using the stick welder with 1/16" rod, and very low current.
There are ideal materials, and methods, then theres what you can get, and your imagination, and thats what you must use. One place to get a closed end steel tube (number of sizes), is a NiCad battery, My latest motor has an AA size one for the displacer cylinder. The 2.5 cc one in my gallery has one for the displacer. A D size battery would be an ideal size for a cylinder made from a vacuum cleaner tube, it would be a little short on its own but this would be easy to overcome. You'v just got to find the dead batteries, the AA ones are easy, but D size are less common, Have a look at stainless steel salt shakers. Ian S C