Hey All, I'm having a bit of a head scratcher concerning some odd things I'm seeing with my Tormach digital probe, the one they call the Digitizing probe in PathPilot.
Had some problems getting good results on a project a couple of weeks ago, and found the the stylus had actually started to unscrew from the probe body. I set it aside to finish the project and just got back to it yesterday.. After re-tightening the stylus, I ran the probe calibration routines in PathPilot and got it setup to within a tenth on the machine.
However in double checking with a 1 inch gauge block I saw a consistent error of minus about .0018". This stayed constant within a tenth or two, no matter whether probing in X or Y and with many variations of probe orientation in the spindle.
I was puzzled trying to reconcile the calibration results with the block measurements. I tried other sizes of gauge blocks, up to 3" and the error stayed constant, didn't increase with length of the block.
I was kind of stumped trying to understand what was going on, then today I probed a precision ring with an accurate bore diameter of 1.1107" and still got the same error. I know that stylus tip ball diameters have an "effective diameter" than is different from their physical diameter, to account for things like stylus flex and others.
So I started changing the tip diameter in the tool table, trying to get a measurement that matched the know diameter of the ring bore, and eventually I got a setting that gave the correct reading within a tenth on the DRO. I then measured a few different gauge blocks and got good results with them also.
So the point of this long-winded post is that to get the proper readings on the test pieces, I had to enter a diameter that was less that the physical diameter of the nominal 5 mm ball, 0.1947" vs 0.1965", as measured with a good micrometer.
So, bottom line, I'm asking if I'm fooling myself seeing good measurements now, is it just luck, or is the diameter adjustment causing accurate measurements? The reason I'm concerned about it is that I have never heard of the "effective diameter" being less than the measured diameter.
Ant thoughts on the subject would be much appreciated.
Terrt