Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: Beerfizz on November 21, 2009, 06:42:45 PM

Hi,
I have a cnc'd mini mill which I drive with Mach 3. I use servos rather than steppers and Geco drivers.
I generate the GCode with OneCNC.
I do have some backlash on my X axis which I remove the backlash feature within Mach 3. I believe I have this set to .0025.
When I cut a circle, the circle is not completely round there appears to be a flat area on one side aligned with the X axis which is maybe 2015 degrees of the circle. This flat area is maybe 1020 thou shallow.
Below is a fragment o the GCode... If anyone has any suggestions I would really appreciate it.
N00120 Z0.05
N00130 G01 Z0.025 F6.0
N00140 X1.8623 Y0.0564 F12.0
N00150 G03 X1.8095 Y0.1035 I0.0029 J0.0499
N00160 G02 X1.8125 Y0. I1.8095 J0.1035
N00170 X1.8095 Y0.1035 I1.8125 J0.
N00180 G03 X1.8566 Y0.1562 I0.0499 J0.0029
N00190 G01 X1.9065 Y0.1591
N00200 G00 Z0.2
N00210 X1.9122 Y0.0593
N00220 Z0.025
N00230 G01 Z0.05 F6.0
N00240 X1.8623 Y0.0564 F12.0
N00250 G03 X1.8095 Y0.1035 I0.0029 J0.0499
N00260 G02 X1.8125 Y0. I1.8095 J0.1035
N00270 X1.8095 Y0.1035 I1.8125 J0.
N00280 G03 X1.8566 Y0.1562 I0.0499 J0.0029
N00290 G01 X1.9065 Y0.1591
N00300 G00 Z0.2
N00310 X1.9122 Y0.0593
N00320 Z0.

Get rid of the backlash. Software backlash helps, but there's no substitute from geting rid of the backlash on the machine.

Doesnt backlash cause 2 distinctive bumps 180 degrees apart, not a flat on 1 side? Though I agree, backlash reduction is best.

Your code seems to have a small arc at the right hand side of the circle, possibly this is your problem. Line N00160 goes almost right round then N00170 does the last part of the move, this is likely where your problem lies. If you deleted line N00170 and made line N00160 go to the position line N00150 is it should be better, you will have to do the same for the next depth.
Hood

Try this code
N00120 g0Z0.05
N00130 G01 Z0.025 F6.0
N00140 X1.8623 Y0.0564 F12.0
N00150 G03 X1.8095 Y0.1035 I0.0029 J0.0499
N00160 G02 X1.8095 Y0.1035 I1.8095 J0.1035
(N00170 X1.8095 Y0.1035 I1.8125 J0.)
N00180 G03 X1.8566 Y0.1562 I0.0499 J0.0029
N00190 G01 X1.9065 Y0.1591
N00200 G00 Z0.2
N00210 X1.9122 Y0.0593
N00220 Z0.025
N00230 G01 Z0.05 F6.0
N00240 X1.8623 Y0.0564 F12.0
N00250 G03 X1.8095 Y0.1035 I0.0029 J0.0499
N00260 G02 X1.8095 Y0.1035 I1.8095 J0.1035
(N00270 X1.8095 Y0.1035 I1.8125 J0.)
N00280 G03 X1.8566 Y0.1562 I0.0499 J0.0029
N00290 G01 X1.9065 Y0.1591
N00300 G00 Z0.2
N00310 X1.9122 Y0.0593
N00320 Z0.