# Whats inside a micrometer



## savarin (Jan 13, 2019)

I'm still tidying my workshop and in the process discovered the Foucault tester I made a while ago had become covered in rat crap and pee.
This had rusted and stuck the micrometers so they wouldnt turn. so I stripped them apart for some serious cleaning.


Thats all the corrosion left after cleaning and reassembling as I only thought of taking pics after it was stripped down.
The anvil has been cut off as the body is held with a screw to a large flat plate.
I had never given any thought as to what was inside them but had a rough idea regarding a nice smooth tight thread.


The scale on the top barrel is just a tight slip fit over the threaded part thats screwed into the anvil part.
That ring is actually a threaded collar that tightens up on the threaded part and I assume tightens up the internal thread to remove any backlash.
The movable threaded shaft is held in the tapered collar that is a tight push fit in the end of the bottom barrel.
The screw that the thimble is held together with screws into the end of the movable shaft pulling into the taper thus spreading it and holding it firmly in the barrel.
Interesting and very simple.
In practice this micrometer moves a sliding stage which is why there is no anvil.


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## mmcmdl (Jan 13, 2019)

I know what's in a Best Test indicator ! I found out the hard way .


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## Bi11Hudson (Jan 13, 2019)

I have some taps for 40TPI, from way back when I did instrument work, long before computers were so widespread. I have since added a few to make a set. 0.025" per revolution has its' points. Or did, back when.

The one I'm thinking of is 3/4 inch by 40 TPI. I've thought to make a (very) large micrometer, mostly just for chuckles. Your photos provide a little insite into construction to make it a practical (if not very useful) project. I knew there wasn't much to one, but never got deep into it. Maybe now it's a go.


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## C-Bag (Jan 13, 2019)

Usually when something is toast I'm pretty bold about taking it apart to find out what's wrong and how it works. But there's a limit and this is mine. I got in a "lot" of measuring tools a B&S 202 mech digital 2"-3" outside mic. It's clockwork was all wonky and the numbers in the "digital" windows weren't corresponding. So I set it aside. But recently I happened to pick it up and for some odd reason it seems to be working!?!? I looked it up and it's a pretty hi $$ item that the few who own them are afraid to use but fascinated by. The few places that would repair it start at $350 so that ain't going to happen. It looks like maybe a screw is missing in the thimble but after some thought that can't be right as if it was tightened down into the slot on the body it would stop it from turning, right?


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