Bore micrometer (Intrimik, holtest) lapping

wehnelt · Nov 9, 2020

I bought some bore gages on eBay and the anvils are pretty horrifically pitted. How are these anvils lapped? Can you just use a cylindrical lap? By this I mean take a cast iron round, drill it and hone it. How do you tension the anvils against the lap? Do you spin the gage or the lap? Do you even lap the anvils in situ or do you use a tool? Crucially, what is the radius of the anvils? I’m most curious how this is done professionally.

Paolo_MD · Nov 10, 2020

At least on the gages I have, the tips of the anvils are spherical, rather than cylindrical. The radius has to be smaller than the radius of the smallest hole you can measure with that gage.

Paolo

TGTool · Nov 10, 2020

I suppose that means you could make a dimple in the end of a rod with the appropriate size ball end mill and use that in a hand drill with lapping compound.

The spherical ends mean that the error in measurement from being out of square is much smaller than if the cylindrical sections were cocked.

Conrad Hoffman · Nov 10, 2020

Look up how they polish lenses. When I do stuff like this, I make a tool with about the right radius using a ball end mill or something custom if a lot of lapping is needed. Hard material if a lot of lapping is required, something soft like maple if just a polish. Rotate both the part and the lap. I put the part in the lathe and the lapping tool in a Moto-tool or similar. Diamond paste as needed. It can help if you put some grooves in the lap. Move the tool over an arc to keep everything spherical.

EmGo · Nov 10, 2020

TGTool said:
The spherical ends mean that the error in measurement from being out of square is much smaller than if the cylindrical sections were cocked.

Intermics (Etalon), at least the ones I had, had part-cylindrical-on-the-ends anvils. When you snugged the mic in the bore, it didn't rock around at all. They were arced at the minimum measuring distance.

Which means, if you lapped them at an angle, then they'd possibly measure funny. Something to be careful of, I guess.

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Bore micrometer (Intrimik, holtest) lapping

wehnelt

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TGTool

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Conrad Hoffman

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EmGo

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