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Thread: Micrometer "feel"

  1. #1
    Join Date
    Mar 2008
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    Default Micrometer "feel"

    Starrett tells me that after their micrometers are thread ground they are lapped.

    I have some micrometers that are very smooth and have a great "feel" to them. I have others that aren't very smooth and that don't have the "feel / smoothness" that I prefer.

    I wondered if anyone has every lapped a micrometer to make it smoother and how it worked out? If you did what kind of lapping compound did you use and what grit(s) did you use?

  2. #2
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    I lapped one that had some rust damage to the threads.I used plain,white,cheap toothpaste.It has a mild abrasive in it and does a good fine lap with a little patience.
    I just need one more tool,just one!

  3. #3
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    I can't speak to exactly how starrett laps the threads, but when stuff is lapped, its lapped against a lap - not its mating parts. doing that would just increase clearance making it a sloppy fit. lapping can put exceptional finishes on, but I can't see it being a trivial task making the thread laps especially when you can by a Starrett mic new for a hundred and something or on ebay for 20 - 30 bucks

  4. #4
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    Quote Originally Posted by Mcgyver
    I can't speak to exactly how starrett laps the threads, but when stuff is lapped, its lapped against a lap - not its mating parts. doing that would just increase clearance making it a sloppy fit. lapping can put exceptional finishes on, but I can't see it being a trivial task making the thread laps especially when you can by a Starrett mic new for a hundred and something or on ebay for 20 - 30 bucks
    I'm told by Starrett tech support that they lap the mating parts of a micrometer together. Still trying to find out what they use for a lapping compound.

  5. #5
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    Quote Originally Posted by Neil Jones
    I'm told by Starrett tech support that they lap the mating parts of a micrometer together. Still trying to find out what they use for a lapping compound.
    then i stand corrected. for lapping in general that's not the way to do it as you cant control how/where material is removed, although i guess if the compound was so fine it barely removed anything....maybe it is toothpaste they're using .

  6. #6
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    Must be...my micrometers have never had any cavities!

    David
    Montezuma, IA

  7. #7
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    Since the mics have a take-up for thread wear, lapping could be done with anything which won't "charge" into the parts...... It won't make the parts sloppy, since you can adjust them back into any desired state.

  8. #8
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    When I was young and dumb, i lapped a Craftsman mic with valve grinding compound.

    Needless to say, valve grinding compound is waaaaay too coarse for lapping a mic.

    Nonetheless, the mic worked much better after lapping.

    Haven't tried lapping mics since then, but I've been tempted, because I have a set of import mics that are next to useless because the "feel" is so rotten. You can't get consistent readings because the "feel" is too rough.

    First thing to try is merely drenching the threads with oil. That fixes a lot of them.

    My knock-around shop mic (the one that sometimes gets dropped on the floor and otherwise abused) is a Horror Fright that was worthless when new due to the crummy "feel." I drenched it with Kroil and that, combined with several years daily use, resulted in a mic that works just as well as any name brand.

  9. #9
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    I would be cautious about lapping a mike. The fit of the threads is very important to the accuracy and repetability of the readings. In fact, I would not do so at all unless the nut was adjustable to take up any slack you may create.

    On fine threads I have made, I find that a good quality grease (or oil) will improve the feel a lot and is removable if you don't get the results you want. Try that first.
    Paul A.

    Make it fit.
    You can't win and there is a penalty for trying!

  10. #10
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    When I took a tour of the Starrett plant in Athol a few years ago, I actually saw them doing this.....

    A row of guys sitting at benches, with a geared "speeder" setup they can clamp a micrometer in and turn the spindle quickly. They apply some very watery (though I assume it's really thin oil, not water) lapping compound, spin the spindle, test the "feel," take out the spindle and bang it on a lead block if it feels slightly mis-aligned...repeat until they're satisfied. They are FAST -- no more than a couple minutes a micrometer, as I recall. But they are truly hand-fitted. I would hesitate to do it myself. Those guys have had a lot of practice.
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