Author Topic: Finishing piston o.d. with toolpost grinder  (Read 1355 times)

Offline Brian Rupnow

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Finishing piston o.d. with toolpost grinder
« on: January 16, 2022, 04:45:05 PM »
This is something I haven't done before, and I'm soliciting information from anybody that has. I have a new toolpost grinder from Little Machine Shop. (It doesn't actually fit on the toolpost but bolts to the topslide---Go figure???). I want to make a new cast iron piston, and hold the o.d. to +/- 0.001". Can I use the toolpost grinder to grind the o.d. of my piston to finished diameter? I would leave the piston attached to it's parent metal and turn it from  piece of 1" diameter stock, then turn it with conventional mill tooling to 0.880" diameter, then without changing my set-up, grind the o.d. of the piston down to the size I require. ---About 0.876". It sounds logical to me, but again, it's something I haven't done before.---Brian

Offline TerryWerm

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Re: Finishing piston o.d. with toolpost grinder
« Reply #1 on: January 16, 2022, 07:24:24 PM »
I see no reason why you could not. Way back in high school I built my very first steam engine which utilized a piston that was .500" in diameter. I first bored and lapped the cylinder bore, then ground the piston to fit. It used no rings whatsoever and was a very close fit in the bore. It worked great! Sadly, that engine disappeared years ago during one of my moves.

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Offline GWRdriver

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Re: Finishing piston o.d. with toolpost grinder
« Reply #2 on: January 17, 2022, 09:07:15 PM »
I fully support that you do the job the way you see fit.  I do jobs "the hard way" occasionally too.  But with the parameters you quote, I wonder why you don't turn the piston in the conventional way?  If it's good cast iron, a well-honed spoon bit will put a bright finish on your piston, and well within your tolerance.  I have a toolpost grinder but not enough experience with it to advise you there, but it seems a bit of overkill given your tolerance.


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