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Brown and Sharpe #250 Caliper Micrometer Calibration and Disassembly

Dennis LaMonica

Plastic
Joined
Apr 16, 2021
I am reaching out for some help. I had trouble with this post as it is my first and probably have it in the incorrect thread.

I have a B&S #250 Caliper/Mic that is in pristine condition. I had a very difficult time zeroing out the barrel and thimble. It took a LOT of force to turn the barrel with the small wrench that is supplied with the Mic.

The Mic has about .017 backlash. I would assume that there would be an internal tapered split nut that would adjust the backlash. I have tried to disassemble the Mic but cannot figure out how to disassemble it. I took it to the guy who calibrates the measuring instruments for a large machine shop near me and he cannot take it apart or figure it out. Maybe it "predates" him.

I am thinking that there may be some internal corrosion because of the difficulty turning the barrel. When I get it back, I am going to soak it in a penetrant.

But the question is: how is this mic disassembled.

I am attaching a link to a photo off of the web and maybe a thumbnail??

My mic is in NEW AND PRISTINE condition.

BTW I am not a machinist.

https://www.picclickimg.com/d/w1600/...er-Caliper.jpg
 

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  • Vintage-Brown-Sharpe-Inside-Micrometer-Caliper.jpg
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0.017 backlash is a lot with respect to a micrometer thread, which I assume is 40 tpi (0.025" pitch). I'd suspect that the connection between the moveable anvil tube and the thimble is loose.

Old, never-adjusted for 50 years barrels can be a beeyatch. With Starretts, I take them apart, clean and polish a bit (at least to get any oxidation or corrosion and old grease off) and then re-grease and assemble. Oil for the threads.
 
To find out how those old micrometers were built, the patent literature is invaluable. The following URL takes you to Vintage Machinery's list of B&S patents. Look at those titled Micrometer Caliper or the like. Even if that exact micrometer isn't seen, the likely design possibilities will become clear. You most likely need to take the micrometer apart, then clean and lubricate it before reassembly. Then it'll be good for another century of service. By the way, the B&S model 250 is listed in the 1916 full catalog, around page 480.

Brown & Sharpe Mfg. Co. - Assigned Patents | VintageMachinery.org
 








 
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