Selection of Optical Flat for Vernier Calipers and Micrometer

Not sure why your doing what your doing. How precise are you trying to get. Typically for my precision I would not use vernier calipers. I only use these for quick reads in the field or work stations. Precision of this unit can be quite varying. I would suggest you discuss this with a good quality control manager or tooling engineer to achieve the proper materials need to completed the task at hand.

Milo,

You are a fountain of wisdom.

I agree with lyn. A well worded explanation about optical flats. GA.

But, I have to wonder... "I want to measure the flatness of vernier caliper and micrometers 100mm to 1000 mm." together with "I measure parallelism by measuring gauge block...", is perhaps a language barrier in place, or perhaps a misunderstanding by our OP of the function of optical flats?

Or, does our OP believe he has two different issues to resolve?

Regarding mixing units: AH has said "We have been moving to the metric system inch by inch." Ain't it the truth.

Lyn, Doorman, Thanks.

I suspect that the OP was told that he can use optical flat to verify, but not told how that will actually work.

They may think it is just some more super precise gage block, hence "2 sided vs 1 sided."

I'll let someone else explain the ansi y 14.5 nomenclature issues, I just wanted to clarify how the Optical flat actually is used. And can be used to determine departure from flatness.

Milo

Thanks for guidance

If i buy 12 to 12.375 mm TESA optical flat for micrometers ( 0 - 500 mm)

and 75 mm Optical flat for vernier (0 - 1000 mm) is it ok?

Please address my second question regarding the measuring of parallalism

34.5 has given a nice explanation of the parallelism issue.

I really don't feel comfortable discussing the GDT stuff, that's not my gig.

If the sizes of the flats you are proposing are adequate to cover the working surfaces to be checked, then why wouldn't it be OK?

Good luck on your work with this.

MIlo

Many verniers have adjustment for parallel - new ones may not be set correctly.

Generally, if something thin like shim, is held in the jaws, using the thumb-wheel pressure, it should be uniformly clamped.

If it easily swivels, you can see where the jaws are 'closed' or 'open', by observing where the center of the swivel is.

However verniers are not a high precision tool, so don't expect too much.

The same test will tell if a micrometer is not parallel. Again, use the ratchet, not a guess at measuring pressure.

Gauge blocks will tell if the 'number' is wrong.

Be very careful everything is clean and inspect all jaw faces for embedded particles, scratches, or burrs - before attempting any test.

I think this covers that mechanical inspection part & Milo has done a great post on optical flats.

_{(thanks for the trip down college memory lane Milo and GA)}

40-60 µm measured across the length of the jaw seems quite a lot. Another way to check this would be with a measuring machine , contact or optical type or even with a projector.

Just a thought, an optical flat is not cheap, then you need the monochromatic light to use it. Unless you're checking several verniers it might be cheaper to just buy new ones with traceable calibration.