Ron Ginger wrote: >> I have some Gcodes where the I and J are in absolute coordinates, EMC2 seems >> to like I and J in incremental coordinates, is there a simple way, or >> something that will enable EMC2 to read these Gcodes. >> >> Regards >> >> Dave > > Mach3 supports both, G90.1 sets to absolute mode, G91.1 sets to > incremental mode. Its valid to change it on the fly within a program. >
That seems like it might be a useful feature. I've started implementing it in EMC2, but as usual when you look at the details, some tricky cases show up. Here is what I'm planning: Right now, IJ arcs require you to supply at least one of the coordinates, otherwise it reports an error. Things like: G2 I1 are OK - that means make a complete circle that starts where you are now, goes around a point 1 unit to the right, and return to the starting point. In the default G91.1 incremental IJK mode, nothing at all will change. In the new G90.1 absolute IJK mode, that same line is ambiguous. Where is the center of the circle? Is it at X=1, Y=(whatever the last J word was)? That might be what you'd expect, since when you omit X, Y, or Z from a move, it uses the current value. But for I and J the "current value" isn't as well defined. Is it the center of the last arc? What if I or J was used in a canned cycle a few lines up? Should it be that value? The Mach manual says "In Absolute it will, of course usually be necessary to use both I and J words unless by chance the arc's centre is at the origin." So Mach is using zero if you don't specify I or J (or K, depending on the plane). I don't see any clear reason for a user to expect one approach or the other. Whichever I do, somebody is going to be unpleasantly surprised when they leave out an I or J and the arc isn't where they want it. So, I'm going to require both coordinates when in G90.1 absolute mode. I think it is better to stop and print an error (during the preview phase if running Axis), than to make a cut somewhere it isn't expected. Comments and suggestions are welcome, but if you want to make I/J/K optional in absolute mode, be prepared to define exactly what will happen in all cases, and come up with very good reasons to justify the additional complexity. Regards, John Kasunich ------------------------------------------------------------------------- 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 Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
