Hi all, For once I'm going to crow rather than eat crow. Discussions with Matt Shaver yielded an idea for a probe that was not the classical Renishaw ball and bar design.
To wit: Drill and ream 0.187 holes in a disk on a 2" bolt circle and press 0.1875 ground dowel pins into the hole. Arrange so they protrude approx .3". Drill a hole in the center of the disk and tap 1/4-28 to attach the probe. You will note set screws in the pic since I didn't have an undersize reamer. Mill holes 0.8" dia in another disk on the same bolt circle. Make cups in .75 dia x .5" cylinders by drilling with a #2 drill/countersink. Put teflon washers in the holes in disk and float the cups in epoxy using the dowel pins as a jig to align the cups. Tap the cups with a 4-40 to attach electrical connections. The logic utilizes the inverting inputs on a hal logic 3 input OR to digital inputs on the stg card. A wire off the disk with the pins goes to digital ground. No pullups were necessary. see http://imagebin.ca/view/UHmqcPz.html Now for the proof of the pudding. Used G38.3 probe a ground surface to check Z repeatability. G code was provided by a C program that simply looped. (PROBEOPEN dataset_name) and (PROBECLOSE) were used to accumulate the data. AFIK if one uses a path in the dataset name then spacing between the PROBEOPEN and the dataset name is not critical; otherwise extra spaces i.e. > 1 will be prepended to the data set name. Ask me how I know. ;-) For each test reps = 30. In like manner I probed the bed at 1" intervals and also used movements in X to probe the side of a ground bar. Note: resolution of the axes are 1 um in X and Y and about 1.5 um in Z. encoders are on the ball screw for X and Y and on the servo motor for Z. Results: std dev. X probe: 0.00022" Z probe: 0.000267" Bed probe: 0.000634" I think I can live with these numbers for a shop-built probe. ;-) Many thanks to those hard working (and I might add bright) people that created the various components that made this this implementation possible. Dave ------------------------------------------------------------------------------ Join us December 9, 2009 for the Red Hat Virtual Experience, a free event focused on virtualization and cloud computing. Attend in-depth sessions from your desk. Your couch. Anywhere. http://p.sf.net/sfu/redhat-sfdev2dev _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
