Tool Mitutoyo digital reading low -- is this a known problem?

[Birkhoff]

This is an older Mitu CD6-CSX that has seen only light use. Have a job here setting shims in mechanical injectors so I wanted a quick and reliable way to measure them from stacks that I have laying around. Quick yes. Reliable, not so much. They weren't measuring to known stock thicknesses with the Mitu so I checked against my mic and vernier. Both of those read correctly, but the Mitu is about 2 thou or .05 mm low quite consistently. Replaced battery; checked for jaw parallel, multiple reset of zero -- all good. Pulled out my 1 inch and 2 inch standards. Same thing, reading .0025 low at 1 inch and .0020 at 2 inch. I know the last digit is fragile.

I assume these things are constructed with glass scales so if they work, shouldn't they be accurate? Is there a reset or calibration procedure?

I have used it a lot for the sheer convenience, but now that I can't trust it, I guess it's back to the old Mitu vernier for a while.

 

[Susquatch]

This is an older Mitu CD6-CSX that has seen only light use. Have a job here setting shims in mechanical injectors so I wanted a quick and reliable way to measure them from stacks that I have laying around. Quick yes. Reliable, not so much. They weren't measuring to known stock thicknesses with the Mitu so I checked against my mic and vernier. Both of those read correctly, but the Mitu is about 2 thou or .05 mm low quite consistently. Replaced battery; checked for jaw parallel, multiple reset of zero -- all good. Pulled out my 1 inch and 2 inch standards. Same thing, reading .0025 low at 1 inch and .0020 at 2 inch. I know the last digit is fragile.

I assume these things are constructed with glass scales so if they work, shouldn't they be accurate? Is there a reset or calibration procedure?

I have used it a lot for the sheer convenience, but now that I can't trust it, I guess it's back to the old Mitu vernier for a while.

I have an older cd6 that works just fine - albeit no auto off. Never had the problem you describe.

I suspect there is dirt between the jaws or a burr.

The Calibration process is simple.

1. Clean the Jaws with a lint free cloth and alcohol.
2. Fully close the Jaws.
3. Check for no light between the Jaws and no light between the fingers.
4. Check that there is a sliver of light between the inside fingers when viewed at an angle.
5. Press and hold the "origin" button with a pen for three or four seconds or so.
6. Also press the zero button once.

 

[Birkhoff]

BINGO! Very strong light behind the closed jaws revealed the problem -- the pointy ends of the jaws must have been hit in a drop event -- << looks around for the culprit >> -- a thin parallel line of light through closed jaws. After a very careful stoning of the jaws to remove the burr on the tips and close up the jaws and my old Mitu now reads 1.0000 and 2.0000 respectively on the standards.

I've checked those jaws a few times in front of light, but the light is pretty bad in my basement shop -- lesson learned.
Thanks Sasq.