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Milled circle not completely round
« 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 20-15 degrees of the circle.  This flat area is maybe 10-20 thou shallow.

Below is a fragment o the GCode...   If anyone has any suggestions I would really appreciate it.

Code: [Select]
N00120 Z0.05
N00130 G01 Z-0.025 F6.0
N00140 X1.8623 Y-0.0564 F12.0
N00150 G03 X1.8095 Y-0.1035 I-0.0029 J-0.0499
N00160 G02 X1.8125 Y0. I-1.8095 J0.1035
N00170 X1.8095 Y-0.1035 I-1.8125 J0.
N00180 G03 X1.8566 Y-0.1562 I0.0499 J-0.0029
N00190 G01 X1.9065 Y-0.1591
N00200 G00 Z0.2
N00210 X1.9122 Y-0.0593
N00220 Z0.025
N00230 G01 Z-0.05 F6.0
N00240 X1.8623 Y-0.0564 F12.0
N00250 G03 X1.8095 Y-0.1035 I-0.0029 J-0.0499
N00260 G02 X1.8125 Y0. I-1.8095 J0.1035
N00270 X1.8095 Y-0.1035 I-1.8125 J0.
N00280 G03 X1.8566 Y-0.1562 I0.0499 J-0.0029
N00290 G01 X1.9065 Y-0.1591
N00300 G00 Z0.2
N00310 X1.9122 Y-0.0593
N00320 Z0.

Offline ger21

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Re: Milled circle not completely round
« Reply #1 on: November 21, 2009, 07:03:55 PM »
Get rid of the backlash. Software backlash helps, but there's no substitute from geting rid of the backlash on the machine.
Gerry

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Offline Fastest1

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Re: Milled circle not completely round
« Reply #2 on: November 21, 2009, 07:08:26 PM »
Doesnt backlash cause 2 distinctive bumps 180 degrees apart, not a flat on 1 side? Though I agree, backlash reduction is best.
I want to die in my sleep like my grandfather, not like the passengers in the car! :-)

Offline Hood

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Re: Milled circle not completely round
« Reply #3 on: November 21, 2009, 07:32:56 PM »
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

Offline Hood

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Re: Milled circle not completely round
« Reply #4 on: November 21, 2009, 07:38:13 PM »
Try this code


N00120 g0Z0.05
N00130 G01 Z-0.025 F6.0
N00140 X1.8623 Y-0.0564 F12.0
N00150 G03 X1.8095 Y-0.1035 I-0.0029 J-0.0499
N00160 G02 X1.8095 Y-0.1035 I-1.8095 J0.1035
(N00170 X1.8095 Y-0.1035 I-1.8125 J0.)
N00180 G03 X1.8566 Y-0.1562 I0.0499 J-0.0029
N00190 G01 X1.9065 Y-0.1591
N00200 G00 Z0.2
N00210 X1.9122 Y-0.0593
N00220 Z0.025
N00230 G01 Z-0.05 F6.0
N00240 X1.8623 Y-0.0564 F12.0
N00250 G03 X1.8095 Y-0.1035 I-0.0029 J-0.0499
N00260 G02 X1.8095 Y-0.1035 I-1.8095 J0.1035
(N00270 X1.8095 Y-0.1035 I-1.8125 J0.)
N00280 G03 X1.8566 Y-0.1562 I0.0499 J-0.0029
N00290 G01 X1.9065 Y-0.1591
N00300 G00 Z0.2
N00310 X1.9122 Y-0.0593
N00320 Z0.