Asking for advise on lapping/polishing

Aug 27, 2004 2 Replies
M

Hello everybody,



I'm working on a small sterling engine project and I need to polish a steel piston (dia. 23/32 ") to a close fit into the bronze cylinder. How would I best proceed to lap/polish the internal part of the cylinder. Are there commercially available tools that can do the job, I was thinking of an expandable collet. Making a wooden mandrel with some 1200 grit paper sticked on it and trying to get a smooth finish on the inside surface by hand, seems not the way to do it ?



Thanks and regards,



Marc


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R

You not only need a smooth surface, you need a consistent diameter. The easiest way to achieve that is with a adjustable lap. But you are using bronze and most commercial laps are brass. The lap needs to be a softer material than the cylinder. That leaves aluminum or lead as readily available materials. When I built my Sterling, which has a cast iron cylinder, I purchased an adjustable barrel lap from MSC. It worked very well and my cylinder finished nicely. See

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. You could make a similar lap out of aluminum. A drill press or lathe will provide the driving force.

BTW, graphite makes a superior piston.

Randy

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R

Aluminum or even hard wood.

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