Is my epoxy piston good enough?

[Aviator168]

I casted my first epoxy piston. It drops right through the cylinder if the bottom is opened. If the bottom is sealed, it take a bit more than 2 seconds to travel half inch. Is this piston good enough?

[markombi]

It should take 10 sec to drop

[Aviator168]

I will get something to seal it one way or another. These copper tubes I got never come in perfect round.

[jimlarsen]

Are you doing this test dry, or with oil?

And any time goal (2 seconds or 10 seconds) is somewhat arbitrary because there are many variables, such as weight, distance, diameter, etc.

[Ian S C]

Aviator168, if you want round, find some brass tube, copper tube is made for water pipe mainly, and water does'nt worry what shape the pipe is. ian S C

[speedless]

Hi
In short,Yes
Try it without any lubrication at first,I never lubricate my stirlings.
Jan

[Aviator168]

Are you doing this test dry, or with oil?

And any time goal (2 seconds or 10 seconds) is somewhat arbitrary because there are many variables, such as weight, distance, diameter, etc.

Yes. The test was dry. No oil.
The distance traveled was 1/2 inch, diameter is also 1/2 inch. I have to check the weight of the piston. It is make of epoxy about a bit less than half of an inch in length.

if you want round, find some brass tube, copper tube is made for water pipe mainly, and water does'nt worry what shape the pipe is. ian SC

I use a 1/2" x 1" copper coupler from Home depot. Why would brass tubes be evenly round?

[Ian S C]

Its round 'cos thats the way its made, its generally made to a higher standard than copper. Also it is much better as a cylinder as it has much less friction, and as its harder it wears better. Bronze would be even better, you can get that in the form of bearing bushes either new or, as I do old worn ones from old machinery. Ian S C

[Aviator168]

Its round 'cos thats the way its made, its generally made to a higher standard than copper. Also it is much better as a cylinder as it has much less friction, and as its harder it wears better. Bronze would be even better, you can get that in the form of bearing bushes either new or, as I do old worn ones from old machinery. Ian S C

You are right. I have been machining the parts. However, I am trying to build a one by just using stuff that's commonly available. I just checked on ebay and there are a lot bronze bushings for sale. Regarding to epoxy pistons. Have anyone mix it with graphite powder? The mix I will use is 2 part graphite and 1 part epoxy.

[Ian S C]

With the second hand bushes you'll proberbly have to bore them to true the bore, if they were OK they would'nt be chucked out. If you can get them its a good cheap sourse of materials. Another good cylinder is the cylinder inside an old shock absorber, the rod down the middle, and the outer case are also very handy. Only thing is, its a bit tricky pulling the things to bits without getting oil all over the place. Down at the plunger end of the outer case make a hacksaw cut, go carefully until oil just starts to leak, then aim it into a container, take a cut or two more,the oil will squert. The cylinder you get is designed to work with a cast iron piston ring (some times a plastic one), and not wear out too quick. See the car wreckers yard. Motorbike forks are also good. The rod is chrome plated, but machinable. Ian S C

[Aviator168]

Great ideas.
I got a new bushing. They are cheap. I am just helping my kid for a school project. Mine engines are machined.

[Aviator168]

Just casted another epoxy piston with a bushing. The piston now falls through without seal and stops moving when sealed.

[Ian S C]

Sound as though you might have it, now for the rest of the motor. Ian S C

[Aviator168]

Piston is less than a gram in weight. It requires 75 grams of extra weight to slowly push the piston down when the cylinder is sealed.

[Ian S C]

Does it drop through with the cylinder open? Ian S C