Mics without tenths

[Matt in TN]

I got several sets of mics with my lathe and was surprised to see no tenth (vernier) lines on a few of them - even a Starrett. What's the point of a mic that only measures to thousandths? Is this common, or is there something else I'm missing?

 

[Holescreek]

It was very common up through the 60's. An experienced machinist can usually "read between the lines". I fully expect someone to jump in ant tell me that's not the right way to do it, but it worked for decades for a lot of machinists. I have drawers full of micrometers without the tenths scales.

 

[JimDawson]

+1 what Holescreek said.

 

[Matt in TN]

Interesting - thanks. So if I have a Starrett with no lines and a chinese no-name with lines - which should I use?

The lines make the chinese mic easier to read, but maybe they're not telling me what they're supposed to be telling me...

 

[Holescreek]

As with any measuring instrument you need to check it out. Your Starrett originally came with a 1" diameter standard just for that purpose. If you have access to some gauge blocks you can get a warm fuzzy by checking the measurements at zero, .25",.5" , .875" and 1". If they're all on the line it's good to go. Most micrometers that haven't been abused will be fine. Sometimes the anvils get worn or the mics get dropped and damage occurs to a few of the threads or the spindle gets knocked out of alignment. Not all Chinese measuring instruments are bad, just some are. The issue is figuring out which one you have. Checking anvil flatness and parallelism requires the use of an optical flat.

 

[Uglydog]

I got several sets of mics with my lathe and was surprised to see no tenth (vernier) lines on a few of them - even a Starrett. What's the point of a mic that only measures to thousandths? Is this common, or is there something else I'm missing?

This is a great question.
My machine tool Instructor says I spend to much time getting every project exactly accurate and precise.
He is trying to get us to work within tolerances while making parts.
Some of the parts require tenths others parts just thousands.
He calls it "fit for use".
I'm trying to leave my tenth mics in the drawer, unless I'm working on a part requiring that level of quality.

Daryl
MN

 

[Wreck™Wreck]

He is trying to get us to work within tolerances while making parts.
Some of the parts require tenths others parts just thousands.
He calls it "fit for use".


Daryl
MN

Excellent.
If the customer wants tenth accuracy on "some features of a part" they will put that on the drawing.

Example (that I see daily on drawings)


Tolerances, unless otherwise specified.
0-6"
x .00 +- .010
x.000 +- .005
Above 6"
x .00 +- .020
x .000 +- .010

The important features will look like this:

Dia, .5002 + 0 - .0005 (with an arrow pointing to the feature in question)

If you are making a part for yourself then by all means chase the tenths
if it makes you happy.

I run older CNC (late 90's) lathes everyday, they do not have liquid cooled lead/ball screws, between 7:00 am and Noon the diameters change as they warm up, they couldn't hold tenths in a bucket.