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0-25mm Micrometer's Calibration & Graduations

Spongebob89

Plastic
Joined
Jan 17, 2021
Hi,
I bought my first micrometer 0-25mm and I have three questions if you please.

My first question is the micrometer's jaws in fully close using the ratchet mechanism always didn't show 0mm (Picture 4). Us I understand wants calibration but why Mitutoyo has a a certificate of inspection where shows 0mm (Picture 5)?

My second is (Pictures 1 & 2) where I am measuring an A4/80gr paper sheet and the thimble marks (0,01mm each mark) doesn’t align with the index line of the sleeve, so what is the right measurement; 0,10mm or 0,101 or 1,102 or 1,103 etc or 0,11mm?

My third query is about a figure (Picture 3) on the micrometer’s manual (at the red box); what does this figure means/says? Maybe is it related for my 1 question?


Outside Micrometer with Heat Ins. Plate 0-25mm, 0,01mm
Item number: 102-301
 

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First make sure the anvils are clean. The traditional way, after wiping off any big chunks with fingers, is to close the mic on a piece of clean paper or cardstock tightly enough that your can JUST pull the paper out.

Then make sure that the readings are repeatable. Close it several times on zero and make sure you always get the same reading even if it's not zero. If they're inconsistent you need to trace the problem to dirt or something else.

Then if it closes consistently to a non-zero reading you need to adjust the barrel sleeve. That's the part that reads even millimeters and has the zero line. Your mic should have come with a tiny pin spanner wrench and there will be a hole somewhere to the backside that the wrench fits into. Twist the sleeve so the zero lines are exactly coincident. This is just an adjustment having nothing to do with the mic's accuracy.

I would ordinarily trust the factory test report, but if you want to trust but verify (Thank you Reagan) you can also check the readings against gauge blocks or the 25mm micrometer standard it you have one. To get even more anal about it, test it with gauge block that mean the spindle is at different point in its rotation not simply even turns.

In the red box you'll notice that the mic graduations only resolve evenly to a two place decimal. (The vernier in the lower pic shows how to read three places if you've got the vernier. Nevertheless, in the upper picture it shows how to estimate to the third place. If the lines are offset a complete width, it's moved .002 mm. Overlapping by half the width represents .001mm.
 
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I used the spanner wrench with the tiny pin and I readjusted it because as many as times I did it and I cleaned it I taken the same non zero reading. Now works fine.
Many thanks for your time and your detailed answer.
 








 
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