Hi, Dan, Here is some more detail as to the nature of my problem. I tried origially to post a lengthy description but it choked on it so i'll try to be somewhat abbreviated...
X and Y motors are 1200 oz. in. steppers.
Z motor is a1780 oz. in. stepper
All axes use 5 thread per inch ball screws and 1:2 belt drives.
Mechanically the machine is VERY solid.
Motor drives are Gecko G212
Power supply is a 800VA transformer, rectified into a 27,000 uf capacitor yielding an output of 70VDC.
Breakout board is a PMDX 120.
Now for the problem.
When running repeatability tests such as the program shown on page 5-15 of the Using Mach 3 manusl, each axis repeats and returns to zero perfectly. However, when I changed the program to move 2 axes simultaneously(diagonal), while the DRO says everything is back to zero, one or more of the axes is offset .005” from zero! This corresponds to 50 step increments. The example program is below:
F20G20G90
M98P1234L50
M30
O1234
G1X.1Y.1
G1X0.Y.0
M99
Starting at X 0.0000 and Y 0.0000, when the program as written above ends the X axis has offset exactly +.005”. The Y axis returns to zero perfectly. Does it every time regardless of feedrate, acceleration, etc.
FYI: Motor Tuning info: X and Y Velocity is set to 40, Z is 30. Steps per unit is 20000. Acceleration is set to 4 for all axes. Step pulse is set to 2 u/s per Gecko. I've played with these settings to no avail. The drives are set to 10 microstep per step mode using the jumpers on them.
If I change line 5 of the program to read: G1X.1Y-.1 and run the program, the X axis offsets +.005” and the Y axis offsets -.005”.
If I change line 5 to read: G1X-.1Y-.1 and run it, the X axis returns to zero perfectly, but the Y axis offsets -.005”.
If I change line 5 to read: G1X-.1Y.1 and run it, both axes return to Zero perfectly.
Running any one of these programs repeatedly, continues the offsets: .005, then .005 more etc.
This cumulative offsetting is bothersome. I would suspect some electrical crosstalk but rearranging the wiring etc. hasn't made any difference.