How do you use a micrometer?

[RaisedByWolves]

Methinks that, at least to a point, the method you use to close in on the work, whether it's some clicks or snug the way you like it, should be the same as the method used when zeroing the mic on a calibration block. You can't change the rate or the span, just the zero point and preload. Without going needlessly down into the weeds of the mechanism, that should be the basis for our purposes.

Of course, I could happily chat with @Bone Head about it all day, I cut my teeth in a multi-ISO accredited lab, but that level of depth had a defined purpose. In my shop, tenths are a nice target, but 99.9% of the time the pursuit is esoteric.

I have spent a large part of my career lately to untrain myself from chasing tenths.

Maybe I should say to untrain myself from chasing tenths when .001-.002 would suffice, but there are times you just want a better fit..

 

[nobog]

I have spent a large part of my career lately to untrain myself from chasing tenths.

Maybe I should say to untrain myself from chasing tenths when .001-.002 would suffice, but there are times you just want a better fit..

They make pressure micrometers to take the guess work out of measuring, often used on "softer" (rubber) material.

 

[projectnut]

I have well over a dozen micrometers in the shop ranging i size from 1" to 13". Only about half have the ratchet mechanism. The others require you go by "feel" to get an accurate reading. The easiest way to develop the "feel" is to use a piece of material of a known thickness (diameter) and practice how much force needs to be applied to the thimble to get an accurate reading.

One of the old timers at the shop where I worked suggested using dowel pins as test pieces. Standard sizes are of known tolerance and within +.0001" to +.0003". To test your skills even further you can get some oversized pins and mix them in with the standard size ones. Over size pins are +.0009" to + .00012" larger than the nominal size. They are all but impossible to tell apart visually, but should be apparent when measuring with a micrometer.

You can also include some undersize pins if you want. However, you'll need micrometers that measure down to the 10ths. Undersize pins are .0002" to .0000" under the nominal size.

 

[rabler]

It would take quite a bit of heat to cause that much expansion, depending on the material, this is one reason why running coolant on a machine is a good thing.

In my mind, if I am shooting for micrometer precision instead of caliper precision, I need to think about heat. That's what works for me, but I have to dig out the expansion coefficients for steel or aluminum to get it right.