I've been working on a VF-3 (2006 model I believe) with a TR10 trunion 5 axis mounted to the table, for about 6 months now. I've learned a lot about the probing system as far as calibration and programming for part measurement and am now starting to use it for setup as well. I use a calibrated ring gauge to set probe calibration and when it sets properly it will find position fairly accurately. When I indicate the ring gauge, I will use MDI to go back to the ring and then I'll re-indicate to test the repositioning. If it is off, I'll enter in the changes on the offset page 1 axis at a time until I indicate zero within .0001-.0003 TIR keeping on the low side. This is done with an interapid tenths indicator. Once I'm satisfied with the positioning I will run a full circular calibration for ball offset and vector measure (I use them fairly often). I set the probe length with a parlec height setter and trim the ball in as true as possible at the same time before calibration. After the cal cycle I run a check on the part (boss) and again use MDI and indicator to check that it has found the center correctly.

I've had several instances now where I take the above steps and find the part off by more than .001 TIR from where the probe set it and when going back to the ring gauge (MDI) finding that the ring gauge is no longer in the same position indicated in not 10 min earlier (.0005 TIR or more). When installing the probe, I always have the spindle orient and place the shank with the circle side of the drive lug slots, towards me to ensure it's always in the spindle the same way. The ring is clamped very securely and level on a riser block mounted for secondary ops. It may take 2-3 tries to get the probe to find the gauge position accurately, but when it's finally dialed in, it works very well.

My concern is particularly the repeatablity for positioning. I can clearly see on #558 & #589 (XY cal offset) that they say .0006 and .0003 or something to that effect and it's reflected in that manor when measuring the part. When calibrated correctly I get .0003 and .00005 and measure .0002-.0003 TIR on the part at the worst. Does anyone else see this "floating" positioning when calibrating? Am I expecting to much out of this machine (I expect that I am)? Is this exceeding the machines accuracy? A lot of the parts I run on this have true position call-outs of .002 or less without MMC on features that are on the opposite end from or even cut separately from their datums, so I need this thing to go as close as possible fairly accurately. When cutting from stock (no probing needed), parts will cut wonderfully and are positionaly accurate.

Sorry for the novel. Any thoughts on this would be greatly appretiated.

Thanks
Greg