CMM on mill

Mikewid04 · Jan 26, 2021

Question for everyone. I recently purchased a Haimer mini 3D for my mill. I have no used it yet but combined with the 3 axis DRO, I think this will make a lot of jobs go faster.

My question is, the haimer with the DRO give me .0001” resolution, but without being NIST traceable how can you rely on the dimensions? I looked quite a bit and have never come across a DRO that is NIST traceable.

AJ H · Jan 26, 2021

NIST confirms they were accurate when they left the factory, not at any point after that. Buy some gage blocks and develop a calibration procedure. Send the gage blocks annually to be calibrated by an accredited company. But that set up will never measure .0001 accurately, .001 maybe.

jccaclimber · Jan 27, 2021

Echoing the above and ignoring issues with fixturing, this deserves the same answer I use with "Is my CMM accurate?".

Put in some gauge blocks, ring gauges, class X pin gauges, etc. Measure them and compare to their known values.
Tilt them a bit and see if you can still get the right answer. A lot of the magic in a CMM is the transformations to correct orientation.

Cover the labels, mix them up, and see if you can get the correct answer without knowing what it is in advance.

Repeat as needed.

CarbideBob · Jan 27, 2021

Good glass scales used to come with NIST traceable error reports and maps.This information only good for the scale itself.
The problem in use is that they have to be mounted on a machine tool slide and that is where the real errors start adding up.
On a normal mill even with 1 micron scales and a top of line Renishaw probe I doubt one could hit much better than .001 volumetric accuracy and that would be a very good or brand new machine.
As above, test and retest in differing positions on the machine tool. Plot the curves and decide on a confidence level you are comfortable with.
It is now a measuring system and how good the scale is only one piece of the much larger puzzle.
Bob

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CMM on mill

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