Mystery (to me) mike

[Sshire]

I came across this Starrett 436 Special (1"-2") micrometer

Both anvils have ball ends

It also has "Special" on the barrel

When I checked it against a 1" standard, it reads 1.219

Here's the only other info

I've seen tube micrometers with one ball end, but can't figure out a purpose for this one.
I'm sure someone here is going to look and say "Jeez, everyone knows that this is a ......."
Thanks
Stan

 

[Tin Falcon]

Well mystery is a good description. These look similar to spline mics. Special purpose mic but what purpose I can only guess do you know the original customer > I have seen pictures of caliper for paper industry and steel industry . I thumbed through my current starrett catalog. There are several mics based on the 436 frame.
My best guess for measuring ball screws just a guess
Tin

 

[Jasonb]

There are quite a few double ball ended mics made for measuring pipes or items with two concave surfaces but that does not explain the 0.219" starting point.

Jason

 

[steamer]

For measuring a specific range of DP gears perhaps?

Dave

 

[bezalel2000]

The diameter of the two spheres may explain the 0.219
have you measured them?
It could be zero is 1" centre to centre of the two spheres

Bez

 

[tomrux]

for measuring the bottom of grooves i believe. dont why the plus .219 tho.

Tom

 

[Sshire]

Ok I measured the balls. 0.109.
Don't see why you'd want to measure from the center of the balls. That would be a guess where the center is.
I could see back to back grooves but other than the bottom of gear teeth can't think where you'd encounter that situation.
I'm going to send the pix to Starrett and see if they want to join the mystery mike game.
Thanks to all. I'll report any info from Athol MA. please keep up the suggestions.
Stan

 

[kcmillin]

I think it is like Jason said, between two convex surfaces.

Perhaps it could be for measuring wall thickness between two cylinders. Like on engines or even a missile battery, the holes would have to be pretty big to get the mic in there though.

I would think the .219" starting point is just a casualty of the modification.

That's my 2 bits.

Kel

 

[90LX_Notch]

Starrett makes special one offs. I haven't looked at one of their catalogs in a while but it use to show some of the specials they've made.

It could be anything. Post it up over on Practical Machinist; someone there is sure to know if it's not too obscure.

-Bob

 

[tomrux]

shows in the Starrett catalogue. cant for the life of me clip a page (protected document ???)

for measuring a groove with a rounded profile. ie concave surface.

Tom