Mystery Starrett Micrometer

[SteveM]

I picked this micrometer up at a surplus store.
It was cheap enough to have it just because it was interesting.
Got it home and the barrel says:
"The L.S. Starrett Co. Athol, Mass. U.S.A."

The curved cutout is about 1" diameter.

The barrel, besides having the usual graduations, has the sizes 1.2 to 2.8 market on it, with the graduations being four on those numbers.

In other words, the graduations look like this:
large tick mark - 1.2
small tick mark
medium tick mark
small tick mark
large tick mark - 1.4

So the smallest graduation is 1/2 of whatever the units are.

From 1.2 to 2.2 on the scale is 1/2", so it looks like it's measuring a radius and reading out the diameter.

Is this for measuring a cutter in a boring bar?

Steve

 

[SIP6A]

The micrometer head is Starrett. The rest of it looks shop made, any special tool made by Starrett that I have ever seen was marked on the frame as well as the barrell. Also the workmanship is rather crude by Starrett standards.

 

[John Garner]

While I agree that the frame doesnt look especially like a Starrett family member, the micrometer head certainly does, and the graduation markings on the sleeve aren't "the usual" graduations.

Ok, it's possible that the sleeve could be "aftermarket", but that seems much less likely than an aftermarket frame.

 

[SteveM]

While I agree that the frame doesnt look especially like a Starrett family member, the micrometer head certainly does, and the graduation markings on the sleeve aren't "the usual" graduations.

Ok, it's possible that the sleeve could be "aftermarket", but that seems much less likely than an aftermarket frame.

I thought it could have been something cobbled up, but the fact that the micrometer intentionally reads x2 tells me that the barrel was made for this specific application.

Steve

 

[wheels17]

Are you sure 1.2 to 2.2 is half an inch or is it .3937", and those are centimeter markings?

 

[SteveM]

Are you sure 1.2 to 2.2 is half an inch or is it .3937", and those are centimeter markings?

Yes, I checked with a dial caliper.

Steve

 

[Toolmaker51]

Is it reading offset from a plane; such as a crankshaft or cam still laying in it's plain bearings?
The 'foot' shows a degree of sophistication with the clamp screw detail, not typical of a full-on cobble. If this was checking pitch or diameter in a gearbox or crankcase, there may have not been call for beauty in tooling. Especially if was a one off solution.