material projection on fixture

[skelly]

Good morning all, I have an inherited fixture, built to opposite side of material, my company normally has fixtures build to design side of material. Is it standard to build the fixture using the min. material thickness, if it required to be built to opposite side of material?
I checked the nets using a nominal material thickness offset, but it was out. Then I checked the same points using the min. material thickness and they are good. Thanks in advance.

[Matthew D. Hoedeman]

Good morning all, I have an inherited fixture, built to opposite side of material, my company normally has fixtures build to design side of material. Is it standard to build the fixture using the min. material thickness, if it required to be built to opposite side of material?
I checked the nets using a nominal material thickness offset, but it was out. Then I checked the same points using the min. material thickness and they are good. Thanks in advance.

As far as I know, there is no 'standard' for this. I would think that in general, they would be built to DESIGN thickness of the material. If you deal with sheet metal, you run into this a lot. Some places want the CMM to be able to check the master side of metal, some want to be able to feeler check the master side of metal. No`matter which way they do it, you will either be locating the nets to the opposide side or checking the opposite side. Just wait until you get a customer who has the fixture built with the master side the fixture side and they still want you to give them master-side checks with the CMM. Fortunately, Pcdmis will allow you to do this by using the ACTUAL thickness option instead of the THEO thickness when creating your check points, but it wasn't always this way.

Another concideration for you to take into account is, are your touch-off values correct for the fixture. With the way they have been calibrating CMMS in the last bunch of years, your machine (or the machine of the people who made it) could be off (out of calibration) in linearity. Could you, by adjusting the touch-off values, make it check in tolerance when using the design stock thickness? Some of the fixture we get in here actually check correct to the touch-off values stamped on the fixture, and some do not. Since I know that MY machine IS linear as well as square (from the way it is calibrated), I trust MY numbers more than I do other peoples. If my mahcine were wrong, then ALL the fixtures I get would need this adjustment, not just some. And, if 1 fixture from a source checks correct, then generally others from the same sourse do too. And, the reverse is true as well, if a fixture from a sources needs tweaking on the numbers, then generally the rest do as well.