Hey guys. Could one of you explain this for me. I thought probe compensation was correct prior to a part alignment. Because even without a part alignment there is still a coordinate system within the CMM. Why wouldn't it be correct without a part alignment?
It will 'never' be correct to your part, unless you part is perfectly flat and square to the machine axis.... FOR SINGLE POINTS.
A plane will get the correct probe comp. A sphere will as well.
BUT, a line measured without an alignment will be comped to MACHINE plane, not part plane.
Oh ok. i think i understand now. Thats how i explained it as well. If you hit perfectly in the X Y or Z axis the compensation should be correct relative to the machine axis but it will not be a perfect hit with a perfect 90 degrees from the surface.
It will 'never' be correct to your part, unless you part is perfectly flat and square to the machine axis.... FOR SINGLE POINTS.
A plane will get the correct probe comp. A sphere will as well.
BUT, a line measured without an alignment will be comped to MACHINE plane, not part plane.
Oh ok. i think i understand now. Thats how i explained it as well. If you hit perfectly in the X Y or Z axis the compensation should be correct relative to the machine axis but it will not be a perfect hit with a perfect 90 degrees from the surface.
without an alignment, all probe comp is done to machine axis, except as I noted for true 3D features (plane & sphere). Once you have an alignment, all probe comp for MANUAL features will be to the alignment. This is why 'they' recommend that you measure a plane, then level, before measuring lines/circles so they they comp will be in that plane.
THAT BEING SAID.....
Almost all my parts are checked on custom, part-specific 3-D fixtures.... that are 'supposed' to be all within +/-0.002" (0.050mm) everywhere. A plane I measure on the fixture base SHOULD be parallel with the machine axis (example: ACTL/900.643,326.325,-598.326,-0.0002622,0.000067,1) and that is close enough to measure a line or circle (while still in machine alignment) and not have to worry about it, not to mention that a DCC iterative alignment will then be done on the actual part locators (net pads and locator pins).
