On Sun, Apr 29, 2007 at 03:34:34PM +0200, Sven Mueller wrote: > Chris Radek wrote: > [probe moves] > > > > It would be nice to be able to set tool length offset this way - but > > > currently there is no way to do that, since lengths need to come > > > from the tool table. > > Hmm, I'm still mostly a newbie regarding EMC. But does the above mean > that EMC can't automatically correct for tool length differences unless > you measure these in advance and store them in the tool table?
Well yes and no. In the part of my message you clipped, I mentioned that you could set a G10 offset using the result of a probe. But if you're talking about G43 tool length offset, that's right. As you can see here, http://www.linuxcnc.org/handbook/RS274NGC_3/RS274NGC_33a.html#1013768 G43 takes a tool number, not a length - so yes it is intended that you measure your tools (which are in holders) and put that information in the tool table. The G43 length is measured relative to a "reference" tool, and you use the reference tool when you set the coordinate systems, touch off to the work, etc. Yesterday sat down to change the interpreter so you can specify a length to G43. This is a simple change to make but I quickly found a couple problems/questions: Currently, G43 H- X- Y- Z- changes the tool offset and then causes motion to XYZ with the previously set motion type (G0,1,2,3). I don't see this behavior described in the ngc spec, but I'm afraid to use XYZIJK for something else if people use the current behavior. So that's problem 1 - I don't know how to allow specification of these lengths at the gcode level without breaking existing programs. (If you guys agree that an existing program that uses this behavior is NOT ngc, I'd feel less bad about breaking it.) Even if G43 can take a tool length directly, I couldn't come up with a straightforward way for the user to use that in gcode. Imagining the mill case first because it's simpler: maybe you'd store in a gcode variable the Z coordinate you get when you probe your reference tool. Then when you probe a new tool you'd take the difference and pass that to G43. But if someone doesn't have tool holders at all, I don't know what the reference tool would be, and with no reference tool I don't know what you'd use to touch-off the work. Tool length offset is just that - a length - and to measure a length you need to find the difference between two points. If you probe a tool tip, that's only one. This is problem 2 - I don't quite see a good way for someone to use G43 in this way, after we solve problem 1. Chris ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
