caliper vs micrometer

5487 Views 30 Replies 10 Participants Last post by msredneck, May 10, 2009

msredneck

Discussion Starter · Apr 23, 2009

I have a dial caliper that I use to measure OAL on my reloads.

Sometimes it seems that a micrometer would be handly when I want to measure bullet diameter or maybe the case mouth diameter when I 'm setting the case mouth expander die....yet the dial caliper will sorta do this as well...I guess its a matter of accuracy.

Which brings up another subject...what do you use to "calibrate" your calipers with guess a gauge block is in order here.

http://longislandindicator.com/p164.html

Guess there is no end to the "toys" a reloader must have!

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massair

· #8 · Apr 24, 2009

Finally, something I think I know a bit about! Sure, you close your dial caliper to zero, make sure it reads zero when closed down, and from there on your measurements are only as accurate as the mechanical means turning the dial, typically a toothed rack which rotates a gear.

Micrometers are the same way, except their accuracy depends on a very accurately made screw thread. Typically, the threads in micrometers are hardened and ground, grinding being one of the super-accurate means of finishing close-tolerance metal parts.

Realistically, one-thousandth of an inch, (0.001") is just about the hair's-breath closest one needs to be in reloading ammo. Just my opinion. Take it or leave it.

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massair

· #15 · May 3, 2009

bigsig said:
'Neck, I am a machinist by trade. ........

Hey, if you are an "old-time" machinist, can you tell me HTH could my Dad (Tool & Die Maker, 1930s- 50s) possibly keep track of table position on, say, a Bridgeport mill? Big pad of paper and some kind of secret way of counting turns of the dials?

He never got to see/use digitals, poor guy. I put a set on my Bridgeport when I bought it, about 1990 in Phoenix, used, an old one, but gets my jobs done.

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massair

· #23 · May 7, 2009

For bigsig:

This might interest you. When we designed an automated molding machine years ago, I needed to have two curved steel beams with an "H" cross section made with a 135 inch. plus or minus 0.010" radius. The only horizontal boring mill big enough that I could find was in Wisconsin, I believe in an Allis-Chalmers plant. They declined to take contract work.

Danly Machine Co., in Cicero, Illinois made the beams, using a then-state of the art tape controlled mill which "stepped" the milling cutter in very tiny increments, a few thousandths for each move, to create the curve. The beams were 60" long, so you can see a huge block of steel was needed to start with, and a humongous amount was machined away. They stress-relieved the parts several times during the machining. When we got them, they looked beautiful! Slipped into the supports (they rode on ball bearings), they slid back and forth just perfectly!

I will try to post a pic of the molding machine taken during construction. OK if the pic has a cute chick in it??

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