On Mon, 2008-07-28 at 00:33 -0500, Jon Elson wrote: ... snip > you might be > able to cobble up a substitute by making a disc with a narrow > slot and one of those U-shaped optical sensors from a floppy drive.
I have thought about this, but I wonder how accurate these are. If you want to resolve .0002", I think you typically need angular accuracy to .16 degrees. I guess I could try it to find out. > I have used encoders with index pulses, and the machine will > home to far greater repeatability than I can produce with an > edge finder. Presumably, it is homing to a precisely repeatable > encoder count, which on my Bridgeport is .00005" (50 u-inch). > I can barely attempt to measure that with a Federal Maxxum > electronic indicator, but the various flexes and stictions in > the machone's ways produce more un-repeatability than that. My Hall home sensors and encoder index (like Jons, I think) work very well. > So, presumably, I could re-index to a fixture on the machine the > next day, but I never trusted it enough to do it without at > least checking with an edge finder or coax indicator. > > Jon On my Shizuoka mill with steppers, I have a piece of tape on the ways that I align, then very slowly jog to zero the dials and click Home. My steps are .0005" each, so my home will be anywhere within .0005", which is okay for most of my work. But it's kind of a bother, considering EMC could home automatically with a click, if I had an encoder index. -- Kirk Wallace (California, USA http://www.wallacecompany.com/machine_shop/ Hardinge HNC/EMC CNC lathe, Bridgeport mill conversion, doing XY now, Zubal lathe conversion pending Craftsman AA 109 restoration Shizuoka ST-N/EMC CNC) ------------------------------------------------------------------------- This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK & win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100&url=/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
