Why would an electronic outside micrometer not return to zero?

I may be wrong (I was once before ;)), but my guess would be that the inconsistency is in the ratchet, not necessarily in the measuring mechanism itself. Have you tried repeating measurements by feel without using the ratchet? You should be able to feel just the slightest resistance before the first ratchet click. Zero the mics at that point and repeat your measurements. Relying strictly on feel with both mics, do the Shars readings still consistently disagree with the Starrett readings?

Tom
 
Just a few points of clarification.
  • Mitutoyo says that errors in reading can be caused by excessive turns on the friction or ratcheting thimble. You want to use the least number of clicks before taking a reading; two is acceptable, more may lead to error.
  • If you want to evaluate a mic, put it in a stand or padded vise. This is not just to avoid thermal expansion. It is more to provide stability so you can position your gauge block properly and get an accurate reading. If you really need to know how accurate your tool is, do it right. Hand holding the mic and block is fraught with error.
  • Temperatures do affect readings if you're working at extreme temps. If the shop is really cold and you're measuring a hot work piece with a cold mic then there will be errors; how much, I don't know. If you must know, both the work and the mic have to be at the same temp for several hours before you can reliably read it. If that doesn't work for you, move to Hawaii where temps are not as big of an issue.
  • The advantages for digital tools are as RJ said, and do not underestimate the impact of aging eyes on the ability to read an analog tool. I have some of the finest analog tools made but it's getting harder and harder to see them clearly. If you must go with digitals then invest in good tools. In this category, digital tools, Mitutoyo leads the field.
 
I believe the issue is not so much accuracy as to repeatability under the "same" conditions. The "0" repeatability of 0.001" is quite poor for this level of precision which is usually specified. I prefer the Mitutoyo ratchet thimble, but my larger micrometers are Igaging Absolute's which has no ratchet, the plunger is spring loaded. Both are accurate and repeatable using gauge blocks to the last digit. The Shar's states their resolution 0.00005"/0.001mm Accuracy ±0.00015"/0.003mm, once zeroed I would expect it to repeat within the stated resolution. They have a 1 year warranty,if it is within this period ask to return it.
 
I am wondering how you can compare a digital mic to an analog with a counter dial?
If you really want to get the answer about these mics, send one out to have it calibrated. I bet it wouldn't cost as much as you think, maybe $50. You can use it as a learning experience.
Like I said before, if these mic's bother you that much, throw them in the trash and buy a brand new name brand one and be done with it.

Joe
 
Also like mksj stated above, they may have 5 digit resolution but that doesn't mean they have 5 digit accuracy.
Joe
 
Liljoebrshooter said:
I am wondering how you can compare a digital mic to an analog with a counter dial?
If you really want to get the answer about these mics, send one out to have it calibrated. I bet it wouldn't cost as much as you think, maybe $50. You can use it as a learning experience.
Like I said before, if these mic's bother you that much, throw them in the trash and buy a brand new name brand one and be done with it.

Joe
Click to expand...

After you said that, I bought 14 Starrett mikes.

I wouldn’t throw the Shars in the trash because I can use them for roughing cuts.
 
higgite said:
I may be wrong (I was once before ;)), but my guess would be that the inconsistency is in the ratchet, not necessarily in the measuring mechanism itself. Have you tried repeating measurements by feel without using the ratchet? You should be able to feel just the slightest resistance before the first ratchet click. Zero the mics at that point and repeat your measurements. Relying strictly on feel with both mics, do the Shars readings still consistently disagree with the Starrett readings?

Tom
Click to expand...

I will try this when I get home (in 7 weeks).
 
This discussion made me sit down and compare repeatability back to zero of two outside digital 0-1 micrometers. A Harbor Freight $35 special and a Mitutoyo Digimatic 293-340-30.

The HFT brand returned to 0.0000 from 0.250 10 times in a row (two ratchet clicks)
The Mitutoyo brand returned to 0.000000 from 0.250 8 times and back to -0.00005 twice (two ratchet clicks)

Not sure what this test means, or doesn't mean - except that, although it was in no way a controlled test, it did nothing to shake my confidence that both measure well enough for the hobby work I do.

I also have an old mechanical (made in USA) Craftsman 0-1, 0.0001 and it also returns to zero repeatedly.
 
I bought a PanaVise 391 for $42. I researched micrometer stands for several hours before I made my choice. I was going to joke and say that I bought a Shars micrometer stand.

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