Outer Diameter Measurement with tight Tolerance

[weisusu]

I am working on a measurement method of an outer diameter of a shaft of 0.200" in length. The OD tolerance is +/- 0.00002. The shaft will meet with an inner diameter (bore) of a different part. I'm currently taking OD measurement using a laser micrometer at the following locations:

Multiple OD scan at Z= 0.10". OD are scanned at 0 degree, 90 degree, 145 degree.
Multiple OD scan at Z= 0.15". OD are scanned at 0 degree, 90 degree, 145 degree.
Multiple OD scan at Z= 0.18". OD are scanned at 0 degree, 90 degree, 145 degree.

So I have multiple OD scans at different length of the shaft. The question that I have is that:

- If I were to average all measurement on the same Z plane (i.e. 0.10"), would the average OD gives me a true picture of the OD? Or should I report the maximum OD measurement on the same Z plane because that is a the worst case condition?

- What kind of analysis I can do to ensure that the shaft OD can fit into the "envelope" to ensure that the shaft can fit into the inner diameter of the bore every single time?

 

[unclesyd]

May I ask why such god awful tolerances on a pin going into a hole?

I don't think that averaging will do for your tolerance. As you didn't give the OD of the shaft you may have rotate the shaft to get a max and min measure. As you length is short I don't think camber and straightness will enter into the equation.

I say this as we worked in the sames range 0.000025 and we measure to 0.000002 on a broach we ground with a diameter of 0.0090 +0.00000 - 0.00001. Our broach had a way better tolerance than we needed but our process produced these tolerances.

Here are some papers that might help with correlation of your to the circularity and resulting diameter of your shaft.

http://www.sciencedirect.com/scienc...serid=10&md5=9ccfeed842fe1de0517f0e9e3babe80e

 

[weisusu]

Hello unclesyd:

Thanks for getting back to me. My I know what measurement method you use to measure 0.000002 on a broach?

I am dealing with an assembly with tight OD and ID tolerance such as +/- 0.00006. With this tight of tolerance, best fit OD and ID do not ensure assemblility of the OD into the ID. Questions:

(1) I'm thinking to take minimum circumscribed circle (MCC) for the OD. Do you folks know of any reliable non-contact (laser for instance) that can give MCC?

(2) I'm thinking to take maximum inscribed circle (MIC) for the ID. Do you folks know of any reliable non-contact that can give MIC?

With that tight of a tolerance, gage R&R has been challenging.....

 

[unclesyd]

Sorry for the slow response. I was trying to get some additional information on our manufacturing process. As they have dismantled the site's library and scaled way back on the manufacture of fiber extrusion spinnerettes and tools to make them information is hard to come by.

I can't locate any any definitive data on the broach but did find some correspondence concerning a plug/pin we made by the thousands.

The 0.0090 x 0.015 plugs were gauged using an in house developed capacitance measuring system as well as optical. This measurement was done during an automatic inspection process. Most of the external calibration was done with the cooperation of our European Offices. I believe the actual work was done in Switzerland. How, I can't find out.

The plugs/pins were ground to size from a 1 mm blank on an in house designed center feed grinder using modified Pope spindles. These pins were used to plug drilled and broached holes, snug but without resizing while finishing the spinnerette surface. The plugs were to insure that the edge of the hole had no discernible radius at 100x after finishing.

I am still looking.