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Finishing piston o.d. with toolpost grinder

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  • DR
    replied
    Dumore TP's came with a diamond dresser holder that clamped around the tailstock quill. That was pretty good so for small diameter work you didn't have to crank the cross slide far to dress.

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  • Toolguy
    replied
    Lots of good advice above. I would like to add, the best way to dress the wheel is with a diamond nib clamped to the workpiece or other round bar stock. In the picture below, it's the C clamp looking part just above the wrench. The nib sticks out opposite the clamp screw on the spindle centerline and faces the operator, with the clamp screw in back. The lathe is off for this operation. Then you turn the grinding wheel on and move the carriage side to side, lightly running the face of the wheel across the diamond. This makes the face of the wheel round and parallel to the lathe bedways. You can buy or make this item. Diamond nibs are pretty cheap these days. You want a wheel that won't break down quickly. A smaller wheel with the same specs as a surface grinding wheel would work nicely.

    https://www.ebay.com/itm/30408336257...MAAOSw3ExhAC~l

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  • DR
    replied
    TP grinders are way over rated IMO. They're a hassle because of the need for constantly dressing the small diameter wheels.

    Practice a bit on a variety of materials. And try to get a wheel recommended for cast iron.

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  • Mcgyver
    replied
    That is the basic approach. Include dressing the wheel and if you can best not to turn the grinder off after dressing.....make sure you cover up up everything well for dressing (paper towel and pot magnets is safer than rags). That's when the abrasive grit goes everywhere.

    lathe rotating slowly in the opposite the direction of the wheel.

    If you are grinding for accuracy, its not going to be really any better than using a very sharp tool and creeping up on the final OD. This is because you still have the same infeed resolution challenges. Attaching a 10ths indicator to the cross slide is one way to improve things. I use a digital one which makes easy to switch from imperial to metric.

    Also, lock the compound and tighten the cross slide gib as much as you can stand. That's probably hard on the lathe but its for a short duration. The reason is the vibration of the thing adds a new factor to the operation and can cause the cross slide to walk a bit, or least the flank of the thread can come off the flank of the nut....that can mess you up but if you've got an indicator mounted it should catch it.

    Personally I avoid it unless I need the finish or the material is hardened as its additional time to set up and given the choice I'd rather not subject the machine to abrasives. Except for the those two situations, imo, it doesn't get you much further ahead
    Last edited by Mcgyver; 01-16-2022, 01:09 PM.

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  • brian Rupnow
    started a topic Finishing piston o.d. with toolpost grinder

    Finishing piston o.d. with toolpost grinder

    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
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