Question About Inside Micrometers

[SteveHGraham]

I am thinking about getting a set of inside micrometers. Here's what I'm wondering: do you have to check the micrometer's accuracy every time you change the tube? That kind of kills the convenience. Also, you would need some pretty big outside micrometers.

[John Evans]

In a word yes if you want to use the readings you get directly. I normally use a OD mic to check the reading. I have mics to 12" ,the 6-12 " are range mics with interchangeable anvils . You can confirm the setting with your surface plate and vernier/dial height gauge.

[SteveHGraham]

So basically the inside mikes are useless unless you have a collection of big outside mikes.

[10KPete]

As long as you have carefully calibrated each rod (or tube) you can swap them around and trust the readings. I have a Starrett rod type that's been in the family for about 80 years and routinely rely on it. It's never let me down.

Pete

[SteveHGraham]

So you don't have to calibrate them every time, but you still need a set of outside mikes?

[SteveM]

Some of them have rods that are adjustable, and if you've bought them used, you would need to check them, but once they are adjusted, they should not go out.

Some of them have non-adjustable rods, so they should be good unless they are worn.

Steve

[John Evans]

OK Steve I guess the question is if you are measuring a ID dimension what are you using to measure the mating OD dimension?

[10KPete]

So you don't have to calibrate them every time, but you still need a set of outside mikes?

For many years this mic was used to measure cylinder bores. The dimensions were then given to the machine shop to make the pistons. Everything always fit to tolerance.

Yeah, Dad took 'em in to the shop once in a while to check calibration but he never had more than a 1" mic at home. I have mics up to 4" now, and check the measurements, but never have had to adjust the ID mic on a cal check.

Pete

[SteveHGraham]

Now I'm wondering about my depth micrometer set.

[10KPete]

If you haven't done so, it's a good idea to go through all your measuring tools and check them. At least check them against one another! Do the best you can and if you can get to a standard closer to one you have in shop, take a mic to that. At least that gives you another check. 1-2-3 blocks are good, provided you can measure them with a known good mic, as that sorta covers all the normal sizes. It doesn't matter if the block is 'right on' just that you know what it is...

Pete

[SteveM]

One check you can do on an outside mic is to measure a pin gauge in more than one position.

Measure with the pin gauge parallel to the mic, then perpendicular. Maybe a few other rotations.

If you don't get the same reading, then the jaws are not parallel.

It turns out, there is a metrology shop near my office. I may have a few of my tools checked, particularly the ones used most often, like my 0-1 mic.

Steve

[liveaboard]

I just bought a job lot of mics from ebay; I was trying to work out how to adjust a slightly odd staret 1-2", and discovered it's likely 100 years old!
If it was for anything other than engineering, that would make it valuable.