Finishing piston o.d. with toolpost grinder

[J Tiers]

A) Use a 4 jaw.

B) use a fixture. I'd think the piston needs that anyway unless you do it all in one go (I think you did).

c) Both.

[Doozer]

Running the piston on centers is the ONLY reliable way of taking it in and out
of the lathe and having it perfectly centered and coaxial again.

-Doozer

[brian Rupnow]

I haven't made another piston. I think the only way I could use a toolpost grinder to finish the final outer diameter is to do it without ever removing the piston from the original set-up in the 3 jaw where it was machined. Once the piston is fully machined, there would be nothing left to hang onto if I used the four jaw chuck after originally turning the piston in my 3 jaw chuck. So far, the only real work I have done with the toolpost grinder is to reduce the pilot diameter on some of my counterbore tools..

[Mcgyver]

The only issue I have with grinding the outside diameter of the piston, is that once the piston stock has been removed from my lathes 3 jaw chuck, it will never go back in the same way.

before taking something out of the 3 jaw, put a witness part on one jaw and the part - a simple magic marker line is good enough. Try it and marvel at how the turned section is very close to concentric on remounting the part. Not saying it would be good enough for you in this instance, but its a good trick when the situation permits (non critical stuff).

[J Tiers]

Centers IS best, but you may need to allow for the volume of the center hole in such a small piston.