I don't bother with centering the ball with respect to the probe. I've attached arms to my probe so that I can accurately rotate it 180 degrees against a stop. I then do a calibration:
1. I probe the center of a hole and record the X and Y values (call them X-A and Y-A) 2. I rotate the probe 180 degrees. Probe the same hole and call the values X-B and Y-B. 3. The average of these values is the true center X-C and Y-C. X-B minus X-A is the offset X-O. Similarly for Y-O 4. Now, when I use the probe, I position it the same as it was in step one. I then add X-O and Y-O to the coordinates returned by the probe. (I may have the backwards -- I might have to subtract.) I've written subroutines that record the calibration values and record them. I've generally found that probing is repeatable to within a few tenths. (That's with a cheap -- less than $100 -- probe where the ball is visibly off center.) I should comment that most people seem to probe by approaching in a direction at (relatively) high speed. Then backing off. Then probing again at low speed. I have no evidence that the common process is better than the one I use. I approach at "high" speed. I back off at low speed and note when contact is lost (technically, the switch closes again). That's the probed location. It just works. Ken Kenneth Lerman 55 Main Street Newtown, CT 06470 On Fri, Mar 1, 2019 at 6:03 PM Gene Heskett <ghesk...@shentel.net> wrote: > On Friday 01 March 2019 11:31:45 Jon Elson wrote: > > > On 02/28/2019 10:23 PM, Gene Heskett wrote: > > > Jon, have you considered setting a digital caliper to say > > > .2500" and locking it, then clamping it down well enough > > > it won't slip while you probe its gap. > > > > I homemade a ring with a pretty good inside bore, but it is > > not as good as a real inside mike standard. Anyway, > > measuring a gauge block with the probe lets me do the best I > > can with my CNC mill. I get a combination of machine > > backlash and probe accuracy, no idea how much of each is in > > there. > > > > Jon > > > I just hooked mine up, pretty bad, and so eccentric, around .125" of > wobble at the ball, same diameter as the ball, its going to have to be > locked tight in order to meet the .005 accuracy it claims. 2 problems, > when installed I have, when z is at top of travel, just about the panel > thickness of clearance with its default 2" long probe, to a 3/8" thick > spoil board, so I need to find a very short probe, an inch or less. Once > thats done and it epoxied into place, I may be able to adjust the bottom > spider to remove the eccentricity at the ball. > > I measured a .250" caliper 3 times, came up with .176 once, (.251 with > the ball), .187" once, (.262 with the ball, and .174 (.249 with the > ball) > > But it turned a few degrees so those measurements are exactly the same as > > > > found on the ground behind the male bovine. :) > > Is it worth trying to fix? Or just another way to keep me out of the > bars? > > _______________________________________________ > > Emc-developers mailing list > > Emc-developers@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/emc-developers > > > Cheers, Gene Heskett > -- > "There are four boxes to be used in defense of liberty: > soap, ballot, jury, and ammo. Please use in that order." > -Ed Howdershelt (Author) > Genes Web page <http://geneslinuxbox.net:6309/gene> > > > > _______________________________________________ > Emc-developers mailing list > Emc-developers@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-developers > _______________________________________________ Emc-developers mailing list Emc-developers@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-developers
