Adjusting a Lufkin 680A Inside Micrometer

I recently bought a very used but complete Lufkin 680A Inside Micrometer set (for bores from 1.5" to 8" diameter, resolution 0.001"). I don't
know how old it is, but the holder has a patent number on it (1,615,488, issued 25 Jan 1927), so it's probably from the 1930s. It looks it.
Anyway, I've been cleaning and adjusting it. Everything was a few thousandths short, largely due to wear at the contact tips (which do not appear to be hardened). The extension rods are easily adjusted with a wrench, but how to adjust the micrometer core (screw and scale) is less clear.
I tried to find a patent number for the micrometer itself, but didn't succeed. That isn't to say that none exists.
Does anybody know anything about this micrometer?
Joe Gwinn
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Joseph Gwinn wrote:

Normally on a micrometer the scale is held in a collet, and you can loosen the collet and simply twist the scale. Some come with a little wrench for this purpose. I very strongly doubt that there is several thousandths of an inch of wear on every rod - it's much more likely that the scale is simply off by a few thousandths and that all the rods are well within .001" of correct.
GWE
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Yes. I have a number of micrometers with such collets, and have the little spanner wrenches that come with the micrometers, but there is no obvious way or place to use such a wrench on this unit.
The collet nut that tightens the female body thread upon the male spindle thread is knurled.
The barrel with the index mark (opposite the rotating barrel with the scale) is perfectly smooth, and 0.400" in diameter. On other mikes I have, there is a little hole for a spanner.
The other possibility is to rotate the scale with respect to the spindle, but I don't see how to do this, and am afraid to force it.

I measured each rod individually. All were off a bit, as were the end cones used when no rod is used.
All the handling surfaces were that iron gray matte finish that comes from years of use by grimy hands. There was no rust whatsoever.
I suspect that as the original machinist (and his son?) aged, their waistlines and bores both increased. And they got their money's worth out of this micrometer set.
Joe Gwinn
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if no one gives you the definitive answer in a few days, contact me directly and I'll scan the adjustment instructions that came with my Lufkin set (I have aprox the same set, I think) and email them to you - you can get my email off my web page, www.wbnoble.com

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Actually, I'd like to see them in any case, and would suggest that a high-resolution scan of these instructions would make a fine addition to the dropbox collection.
Thanks,
Joe Gwinn

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ok, posted to drop box as lufkin-instructions (txt and jpg)


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Got it. The only difference between 680A and 680B is that the 680B set has one additional rod, a six-incher. The longest rod in the 680A set is four inches.
Patent number 1,424,383 was the key, reinforcing the instructions, showing how the sleeves are built. I could see the splits when I looked into the annular cavity between spindle and sleeve.
Anyway, the 680A is now re-calibrated. This required polishing 0.0004" off the less-worn cap, making the caps equal, adjusting the micrometer core to read correctly with the two worn caps, and adjusting all the rods to match.
With any luck, this 680A will end up with 100 years of service.
Thanks,
Joe Gwinn

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replying to William Noble, CJCastiglione wrote: Morning all, I was trying to find the instructions for adjusting the Lufkin 608A mics and haven't been successful. Can someone help me out please? Chuck
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replying to William Noble, Joe Rich wrote: William, Can you send me a copy of those instructions also. I have not been able to find a copy on the web yet. Thank you. Joe Rich
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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 Joseph Gwinn, andres padilla wrote: Can someone email me the instructions to adjust the Mic head?
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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 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 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

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
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