On Mon, Jan 21, 2008 at 11:13:45PM +0100, Geert De Pecker wrote: > Steve, > > Front tool. But how would emc know? > > Geert
Well it doesn't, but it does affect which what things like "viewed from above" and "clockwise" mean. Gcode use a right-hand coordinate system. If this is not familiar see: http://en.wikipedia.org/wiki/Right-hand_rule If your lathe has X in front, you probably think of Z pointing to the right and X pointing down to your feet. When you consider the handedness of the coordinate system, this makes Y point away from you. So, you aren't actually "above" the ZX plane, you're under it. This is why G2 and G3 seem reversed to you. Imagine looking up through the table of a mill from below and you will see the same thing (but for the G17 XY plane). If your lathe tool was in back, it would be more natural to think of X pointing up and Z right. This makes Y point toward you and a G2 would in fact look clockwise again. The real answer here is that a G2 arc only appears clockwise when looking from the positive direction of the axis perpendicular to the arc's plane. For you (and me), with our lathes, we have to sit under it in order for this to be the case. But, this IS the behavior we want because the gcode is independent of "tool in front" vs "tool in back". I like to think of G2/G3 as lefthand/righthand arcs. If you take a magic marker and draw G2 on your left hand and G3 on your right, and curve your fingers into arcs like a GI-Joe and stick your thumbs up, you only have to place your thumbs along the positive perpendicular axis to any plane to see the two arc directions for that plane. Chris ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
