measurements to 10 millionths of an inch

alt.machines.cnc, rec.crafts.metalworking measurements to 10 millionths of an inch
Anybody know of a calibration lab or testing facility that can make xyz
measurements of a small sample with a max dimension of about 2 inches. Accurracy should be in the +-10 millionths of an inch range.
Hul
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Are you sure about that 10 millionths accuracy spec? The very best CMMs can only do about 14 millionths over that range. If that is sufficient, you need to find someone who has a Zeiss UPMC Ultra CMM. Remember when measuring to this level, you have to consider very carefully the pattern of points to be collected and how the final dimension is calculated. If you are talking about a flat or nearly flat sample with some sort of pattern, there are optical profilometers that may do the job.
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Optical machines may be fancier than required in this case. The device to be measured is a 3/8 square bar about 2.5 inches long with some steel balls soldered to one side. The points to be measured are the balls themselves and their size is known. A lab having a flat surface with a post imbedded to hold an indicator capable of comparing at 10 millionths plus a full set of gage blocks would be able to make such measurements. A 1x2x3 type of gage with vice like clamping means would be needed but that should be all - hopefully. I've found one outfit that states 70 millionths, but that's pretty far outside the needs here. The 14 millionths you mention would certainly be close enough and I'll add those devices to the search. Thanks--
Hul

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On Jan 6, 4:56 pm, snipped-for-privacy@kbrx.com wrote:

wow- how would you adjust the position of one of those balls if it was soldered out of tolerance ? I suppose a misapplied tap could perpetuate to move the others.
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On Jan 6, 1:56 pm, snipped-for-privacy@kbrx.com wrote:

You are facing a very tough problem.
That come out to 350 nm. I have done a bit on MEMS work and an optical microscope is going to have problems imaging that small of detail. At that tollaerance one is going to have to specify temprature. For example if the rod is steel one deg F of temprature is going to change the lenth ot the bar 12 mico-inches.
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It may be possible to get measurements accurate enough with the simple set-up you describe but do not under estimate the difficulty. To measure the apex of a ball you need a flat anvil on the indicator. But to get 10 millionths accuracy when the anvil contacts the gage block, it would have to be in contact to better than 1 fringe optically. In other words you would really have to wring the anvil onto the gage bock as well as the gage block onto the bottom flat (which would have to be a glass or metal optical flat, not a granite table). This would be tricky. The indicator anvil would also have to be set up perfectly parallel to the bottom flat. Having a very small flat anvil would help a lot. I know I would not trust the measurment of one person or lab for this kind of thing
You might do better using a supermicrometer: http://www.prattandwhitney.com/Content/External_Supermicrometer_C_Horizontal_Comparator.asp But while these have a repeatability of 10 microinches, the accuracy is only 20.
There is also a method for measuring balls where you can directly compare the ball to a gage block stack using two optical flats. It might work here if you have a jig to hold the part vertical. The ball is placed between a pair of optical flats on one side, and a gage block on the other side. Measure the spacing of the fringes formed between the block and the upper optical flat and calculate the angle of the upper flat. Then measure the distance between the edge of the block and the apex of the ball to calculate the height difference between the block and the ball.
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