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wrote:
I have a set of Starrett depth mic's. These are the rod type and I need
to know how to zero the thimble. I am using a gage block and a surface
plate. There doesn't seem to be anywhere where the graduated spindle
turns like it does on an outside mic. Also, the wrench that fits the
nut inside of the thimble seems to adjust the pressure required to turn
the thimble. The only other thing I can think of adjusting is the stop
nut on the rod. These seem to be loctited on and are not movable. Any
advice on getting these zeroed would be greatly appreciated. Thanks,
Steve

I can't say for certain on the Starrett mic's but every other depth mic
I have come across, you have to adjust the nut on the rods. Otherwise
if you adjusted the mic for one rod, it would be out on the rest. Try
some gentle heat from a hot air gun to loosen the loctite, or if you can
get it, some solvent for a day or two. If you do get it loose, try and
use 2 sets of gage blocks to support the mic when adjusting it. This
will reduce the possibility of error from tilt, and you wouldn't have to
hold on to it at all times.