Thread: An idea for a contact grinder.

Yes, there should be a piece that is exactly 2 inches long that is used for calibration. The only one that does not need one is a 0-1 inch mic, in that case it is screwed all the way down till the anvils touch and then is should read zero. (actually the same is true with the 2-3 only you will turn it down to the calibration piece.)

Originally Posted by tintin

Yes, there should be a piece that is exactly 2 inches long that is used for calibration. The only one that does not need one is a 0-1 inch mic, in that case it is screwed all the way down till the anvils touch and then is should read zero. (actually the same is true with the 2-3 only you will turn it down to the calibration piece.)

A nice set of precision gauge blocks is on my medium-goals list... But in the interim, I checked the 2-3" mike using a digital vernier, and it turns out that it's accurate. I shoulda known the nuclear submarine engineer wouldn't have kept around an inaccurate micrometer!

It can just be screwed down to 0.996 or something like that, instead of 1. There's a scale on the internal barrel and when it's properly zeroed its pretty obvious.

The 10 thou part is still mystifying to me. There are a series of marks above the main indicator and they're all numbered, then the barrel has engraved around it 3 columns of numbers, I guess to look up the full precision based on the extra lines on the inner barrel, but how you read that still doesn't make sense to me and I've been too lazy to look it up. It's accuracy to a 10 thousandth does not appear to be the most practical, but thousandths are perfectly comprehensible.

Yeah, in my few years as a tool and die maker i never had to measure down to the 10 thousandths. You have to be a very experienced machinist to be able to maintain accuracy like that (and have some very precise tools to help you do it.)

Originally Posted by tintin

Yeah, in my few years as a tool and die maker i never had to measure down to the 10 thousandths. You have to be a very experienced machinist to be able to maintain accuracy like that (and have some very precise tools to help you do it.)

My instincts are to eyeball everything. It's gotten me into trouble, and I'm trying to get better about it! Hence, a good micrometer around!

I did at least measure the parts I'm replicating for the Power Punch and write down the measurements on a couple of pieces of brass sheet on my workbench so I have no excuses.

I'd be nice to have a micrometer for threads, but so far I'm happy to be a bad machinist and just use the 'will it screw into my power punch' test. We'll see how that goes as soon as I send some of these parts to someone else to use on a different tool. Should be soon! My new collet chuck oughta be here in the next couple days.