Depth micrometer rod adjustment?

amstel1

Starting to get Involved
#1
Hi guys, I wonder if anyone can share with me how to adjust rods on depth micrometers?

I have Mitutoyo 0-4", 0-6" or 0-12", rods are frequently out of tolerance. I tried loosening two hex screws and then moving nut back or forth as needed...and I get it close, but it is almost impossible to get it on zero in timely manner and avoiding thermal expansion.

If there is a simple and quick way or any proper way(I am not sure if I am doing it right), please let me know

Regards
 

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Ninja

Looking for Reality
Staff member
Super Moderator
#2
Howdy,

Typically, the mic will come with an adjustment wrench (do a search for that term and look at the pics...)

After changing extension rod, close the mic to "zero feel" then use the wrench to adjust the reading to zero.

This does not change the incremental movement...it just rotates the whole screw mechanism so you're starting at the right place...

Decent little step by step on the rezero-ing here .

After you do it...best to then measure a "known"...the rods aren't always perfect length...get to know how long they really are...
 

Ninja

Looking for Reality
Staff member
Super Moderator
#3
Oh, just an adder...

Thermal expansion, measured by a hand mic...not gonna happen. There's no way a hand mic can measure thermal expansion of anything 12" or less.
TCE is measured in parts per million per deg C.

A 12" part with TCW of 15ppm/degC shifts 0.18 mils (4.6um) per degreeC. a 3degC shift makes it half a mil (5 tenths) or 14um.
No way I'm ever gonna trust a hand mic to measure that reliably...
and a high TCE is 303 stainless...it's only 9.9ppm/degC, not 15.
 

amstel1

Starting to get Involved
#4
Hi Ninja...

This procedure is to adjust barrel to zero, not the actual rod. That is easy part.

Problems are extension rods, they get out of tolerance and need adjustment. Each one have locking mechanism with two hex screws and a nut. In theory it seems like loosening the two hex screws and then turning the nut left or right, depending where it's needed, then pulling that mechanism with two hex screws close to the nut and tightening two hex screws and also tightening the nut with the small wrench that is provided in the case.
It is easy to get it close to the zero, but almost impossible to get it on the zero. By the time I get there I spend so much time playing with it that it already expanded considerably(rod itself, no the micrometer), even if I get the zero I have to wait several hours do double check if it's really on zero.

This Mitutoyo has 0.001" increments, our in-house tolerance is 0.0005", I usually manage to get it close to that on either side of the scale, but almost impossible to get at least 0.0001" if not 0.0000". There must be easier and quicker way to adjust those.

I spoke to Mitutoyo and they either didn't understand or did not want to share that information with me, they refer me to buy microchecker which I already have. Funny enough, they provide you adjustment wrench for barrel, hex key and wrench for the nut, but no instructions how to zero the rod.

Similar is for the Interchangeable outside micrometer anvils, you have to loosen the nuts and then turn nut up or down as needed and then tighten them both. I found them slightly easier to adjust then these.
 

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Ninja

Looking for Reality
Staff member
Super Moderator
#5
Howdy again...that's why I mentioned:
get to know how long they really are...
A set screw and a lock nut...to precisely adjust to a 0.0005" window...don't bother trying to get that right anytime soon.
That's like using a tape measure to measure the thickness of paper.

Lock the rods down, establish (using a known) how long the rod actually is...and use it for that length.

If it were me, I would do it once to the best I could, and have Loctite on the threads and the set screw...If my 4" rod ended up being 3.9985" so be it...label it as such and use it as what it is (as opposed to constantly fighting to get 4.0000")

HTH
 

Ninja

Looking for Reality
Staff member
Super Moderator
#6
Another adder FWIW... I wouldn't trust a hand mic for 0.001" tolerance anyway.
You ever try to GR&R that?
Best I ever got was a 45% GRR
 

NickV....

Starting to get Involved
#7
Howdy again...that's why I mentioned:


A set screw and a lock nut...to precisely adjust to a 0.0005" window...don't bother trying to get that right anytime soon.
That's like using a tape measure to measure the thickness of paper.

Lock the rods down, establish (using a known) how long the rod actually is...and use it for that length.

If it were me, I would do it once to the best I could, and have Loctite on the threads and the set screw...If my 4" rod ended up being 3.9985" so be it...label it as such and use it as what it is (as opposed to constantly fighting to get 4.0000")

HTH
IMO that seems like a risky scenario for a NC over and over again. The fact that you're relying on the operator to look at the label indicating the "actual" value at zero then your guaranteed to have issues....oops I forgot or I didn't notice the label or the label is missing...etc.. A depth mic is +/-0.001 and to get it within that range is tricky but not impossible with some practice. If you're looking for reliability and something easy to manipulate purchase a dial depth gauge that you can easily zero the dial for each rod being used. They come in 0.0005" graduation as well. But I do like the Loctite idea! I'm doing that next calibration interval.
 

Ninja

Looking for Reality
Staff member
Super Moderator
#8
Fair enough point.

When faced with relying on an operator who is capable of doing something (math), and relying on a gage that is not capable...I'll take the operator.
That said...getting a gage that doesn't need all the fiddling around sounds even better (though more expensive).
 
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