Proper procedure for programming using a fixture

[lost_in_endicott]

Let me preface this by saying that I'm extremely new to CMM programming. After my company bought our CMM, they had a tech come to our plant and he gave a two day crash course on PC-DMIS for us. Since then, I've been combing through the help files and this forum to get our CMM programmed and checking parts.


I'm not at work, so I can't post the code. I have a part where the datums are an outside diameter, the face of the part, and a flat on the internal spline. My fixture is basically a block with a spline that mates up with the part. The flat is very small, so the tool room made the flat parallel with the front edge of the fixture. I use the fixture to pick up 2 of the datums (face and spline flat), and the other datum is directly off of the part( OD).


Up to this point, my program takes manual hits on the part, align, DCC hits on the part, align, hits on the fixture for two of the datums, then checks features on the part. After I initially run a part, I grey out the manual hits and the fixture hits. For us, there are three machining operations, and we have to keep an eye on the true position of a feature on the part. i have two separate programs to check the the part depending on what operation is being machined.


I guess my question is- is it ok to have my fixture hits in the program? I have an inspector that is questioning the validity of the program because the CMM doesn't know where the fixture is, and i don't have a good answer for him, other than the what I've got in the program and the relation of the flat on the spline to the front edge of the part.

[Darrollh]

When you build your alignment, build a man and DCC to the fixture then align the part to it's datums. That's how I would do it.

[Schrocknroll]

If the primary locating function of the fixture is to allow you to rotate relative to the spline, I don't see any issue in probing the fixture only for that purpose. Level to the part, rotate to the fixture, and set the origin on the part. That would be perfectly legitimate.

I have an inspector that is questioning the validity of the program because the CMM doesn't know where the fixture is.

Tell him the CMM doesn't need to know where the fixture is because you're not using it for location, only for orientation. If you rotate to the front of the fixture, the CMM does know the orientation of the fixture.