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General Mach Discussion / slave motor not in sync with master axis motor

« on: July 17, 2009, 12:59:02 AM »

I'll preface this with the fact that I'm fairly new to the CNC world.  I've got a Gecko G540 with the A-axis slaved to the X-axis.  I have two steppers moving the gantry of my router in the x direction.  I cut a lot of circles, some recessed, some through cuts.  What I've noticed is that when the router has made one complete pass it pauses to plunge down a little more in the z direction (I'm cutting 3/4" mdf or 19mm baltic birch typically) and then will start another pass. The A-axis motor will always start moving before the X-axis motor, making the gantry out of square, more and more.  I tried to use a ramp cut down so the motors don't necessarily stop all of the way, but for some reason Mach 3 or the Gecko ignores the Z move in my G-code if it is preceded by both an X and Y move.  The computer monitor shows the Z axis moving down, but the actual z-axis doesn't move.  If the Z move is on it's own line it will move fine. 

So, two questions.  Why isn't the slaved axis starting in sync with the master axis (or vice versa)?  Why won't Mach3 or the Gecko recognize a z move in a line of code like this (G1X6.8124Y3.9731Z-0.0017)?