Simple way of getting a near tight sliding fit on piston and bore?

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WhiskeyHammer

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Is there a simple/low-skill way of getting a near airtight sliding fit on a piston and bore?

I've been mulling this idea:
1) Get a pipe and rod made of the same material that are already pretty close to in ID and OD, the OD of the rod should be larger than the ID of the rod
2) Pop the rod onto a drill chuck and with a fine abrasive reduce, the OD of the rod as until it's a hand-strength press fit with lubrication into the shaft
3) With the rod still on the drill, press the pipe onto the rod, and start the rod spinning at very low speed
4) In my mind, the rod will lap itself against ID of the pipe and eventually you'll get your sliding fit

Will this work? Is there an easier way?

I figure there are a few guys here who've built some ringless pneumatic engines that might have worked out some better techniques.
 

Master

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I usually use cast iron for piston sleeves. I try to run the lathe in and out many times to get the best possible finish. Next I make an aluminum piston that is just a bit under the dimension of the ID of the sleeve. Mineral oil and Bon Ami makes a good slurry. I work it by hand in and out with the con rod on it to be able to control it. When cleaned the piston should be able to slide out of the liner, but it you place your hand over the end of the liner it should not move.
 

kiwi2

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Hi,
I generally bore out the bore using a cutting tool ground to a semicircle which gives a good finish. I then turn the piston on the lathe until it's a really tight fit in the bore. Starting with about 400# wet and dry sand paper I then slowly remove the excess diameter using progressively finer paper as I approach the sort of fit I'm after. I actually ended up using Brasso on a piston for a Stirling engine.
If you want to do a proper job however, this video:
shows what is possible if you want to take the trouble.
Regards,
Alan
 

RonGinger

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If you dont care which part becomes smaller it might work. But I would not call it lapping, it is simply wearing one part out to fit the other. The harder part is the one that will wear- the grit will embed into the softer part and cut the harder one
 

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