Case 6

Master Fixture Calibration

The challenge was to make fine adjustments to a master fixture that was used to machine a mini-van space frame. The master was the same size as the actual mini-van and had 57 locating pads that needed to be located to better than 0.001". A giant coordinate measuring machine was used to measure the position of the locating pads in X, Y, and Z but what adjustments were required to each pad in order to accomplish the final 0.001" tolerance?

The solution was a large spreadsheet that created a best fit linear regression center line for the master fixture and calculated the adjustment required for each of the 57 locating pads. After the calculations were completed and new, corrected pads were installed the measurement process was completed again with a very small number of readjustments required. It is unlikely the tolerance would have ever been achieved without the best fit calculations done by this spreadsheet. Thousands of dollars were saved by reducing the number of iterations required to achieve the tolerance levels.

This massive spreadsheet was created using a very rudimentary, very early version of Lotus 123.


(Click on the picture to see a larger image.)

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