replying to William Noble, Randy wrote:
Is there any chance I could get instructions how to adjust the Lufkin 680
inside tube mic.. I googled it and found you, Thanks

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replying to Randy, CJCastiglione wrote:
Hi Randy
Adjusting the extensions is accomplished by rotating the end piece in or out.
The micrometer head is more of a PITA.
Remove both of the tiny end caps and using a .0001" indicator, make both caps
identical thickness. I used some 400 grit emery cloth on a flat block. Install
the caps on the micrometer head and set it to 1.000" on the barrel. Use a set
of good mics and see which way they're off.. Now dis-assemble the head
completely except for the insert that is light press fit into the barrel. You
need to move the insert in or out to change the reading. I used a bench block
and a gage pin that fit the barrel to bump the insert. Repeat the above steps
until you get it right. It's a PITA. Once you get the head adjusted correctly
then do the extensions. Let me know how you make out.

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replying to CJCastiglione, Randy wrote:
Hi CJ, you were right about calibrating the mic head its self being a PITA
!!!, But I finally did get it ... I knew how to adjust the individual rods
but the Mic itself was a mystery. Its unlike a Starrett that you can easily
adjust. I really do appreciate the Info... Thank you my Friend


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replying to Randy, Dudy wrote:
Does anyone have a copy of the instructions for adjusting the Lufkin 680a?

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On Sat, 27 Feb 2021 00:18:02 +0000, Dudy
wrote:

replying to Randy, Dudy wrote:
Does anyone have a copy of the instructions for adjusting the Lufkin 680a?

I don't know that I do, but US Patent number 1,424,383 is the key.

Enter US1424383 to Google Patents to get a copy.

Joe Gwinn