On 2008-04-23, Richard J Kinch wrote:
I have an old Millers Falls micrometer that somehow is out of calibration
by about a half a thou. How do you adjust these? I've adjusted other
types where you grab the sleeve (Starrett) or the end of the thimble
(Polish import) with a little spanner wrench, but I can't find any such
mechanism on this Millers Falls item. It's been trustworthy for many
decades (from former owners and lately me), made in the USA, and
wonderfully dinged up and cosmetically worn, so I have an attachment to it.

"Millers Falls" -- I think that my first micrometer was by them,
and bought in the shop attached to a commuter train line's station.

IIRC -- that one had only one way to adjust it.

1) There is a small hex just where the small knurled spinner
mates with the spindle. Find an ignition wrench which fits and
loosen this.

2) Pull the thimble away from the body of the micrometer. (There
is a steep taper where they join.

3) Turn the spindle with light finger pressure on the taper until
the micrometer closes. Lock the spindle.

4) Slip the thimble back onto the spindle and align the zero with
the index line.

5) Holding by the thimble, re-tighten the spinner to secure the
thimble to the spindle.

6) Unlock the spindle, and try closing it and make sure that it
comes to zero with the proper feel. (You may need to re-adjust
this a couple of times to get it right.

Note -- this is assuming that the problem is not dirt or grit in
between the spindle face and the anvil face. So -- before you do any of
the above, open it enough to slide a piece of clean white paper in
between, and then close lightly on the paper while you draw it out.
This should remove any grit.

Now if the spindle closes to just below zero, then you may have
badly worn spindle faces. Mine did not have carbide faces, and yours
may not either.

If the spindle and anvil faces are worn, there is a good chance
that they are worn to form a taper which is wider in one rotational
position of the thimble than in another 180 degrees different. The way
to test for this is to close it gently on a quartz flat and observe
under monochromatic light -- typically a selected line from a sodium
vapor light. If it is tapered, you will see bars from one face to the
other. And you really need two of these flats -- one about a
quarter-turn 0.006" thicker than the other, so the spindle will be at 90
degrees to the first setting. If you have this problem, the way to fix
it involves precisions lapping -- which will probably cost you more than
a replacement micrometer of equal quality -- unless you figure out how
to do it yourself.

The taper really will matter only if you have one with the
tenths vernier on the barrel.

You can probably get it close enough for most of your work by
following my suggestions above -- assuming that it is built like mine.
I wish that I knew where it is now. :-)

Enjoy,
DoN.

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