Hi All
Very new cnc and G code so need help. I am testing a new home built by machining a small mounting bracket for a stepper moter. The problem I have is with a pocketing operation in the centre of the bracket. The first pass is ok but the second is off centre in the y axis and  the third also off,and so on. The cumlative error produces a steped pocket at final depth. I am very new to CNC but is this problem related to g90 ,g90.1??
Any help would be appreciated
Thanks

Can you post your code so we can check it?

hi Jerry
Here is the code;
The profile cuts ok the problem is with the pocket
[( Made using CamBam - http://www.cambam.co.uk )
( stepperv3 5/12/2010 9:33:52 PM )
( T0 : 6.0 )
G21 G90 G64 G40
G0 Z1.5
( T0 : 6.0 )
T0 M6
( Profile1 )
G17
M3 S0
G0 X-50.0 Y-33.0
G1 F30.0 Z-1.0
G1 F300.0 X50.0
G3 X53.0 Y-30.0 I0.0 J3.0
G1 Y30.0
G3 X50.0 Y33.0 I-3.0 J0.0
G1 X-50.0
G3 X-53.0 Y30.0 I0.0 J-3.0
G1 Y-30.0
G3 X-50.0 Y-33.0 I3.0 J0.0
G1 F30.0 Z-2.0
G1 F300.0 X50.0
G3 X53.0 Y-30.0 I0.0 J3.0
G1 Y30.0
G3 X50.0 Y33.0 I-3.0 J0.0
G1 X-50.0
G3 X-53.0 Y30.0 I0.0 J-3.0
G1 Y-30.0
G3 X-50.0 Y-33.0 I3.0 J0.0
G1 F30.0 Z-3.0
G1 F300.0 X50.0
G3 X53.0 Y-30.0 I0.0 J3.0
G1 Y30.0
G3 X50.0 Y33.0 I-3.0 J0.0
G1 X-50.0
G3 X-53.0 Y30.0 I0.0 J-3.0
G1 Y-30.0
G3 X-50.0 Y-33.0 I3.0 J0.0
G1 F30.0 Z-4.0
G1 F300.0 X50.0
G3 X53.0 Y-30.0 I0.0 J3.0
G1 Y30.0
G3 X50.0 Y33.0 I-3.0 J0.0
G1 X-50.0
G3 X-53.0 Y30.0 I0.0 J-3.0
G1 Y-30.0
G3 X-50.0 Y-33.0 I3.0 J0.0
G1 F30.0 Z-5.0
G1 F300.0 X50.0
G3 X53.0 Y-30.0 I0.0 J3.0
G1 Y30.0
G3 X50.0 Y33.0 I-3.0 J0.0
G1 X-50.0
G3 X-53.0 Y30.0 I0.0 J-3.0
G1 Y-30.0
G3 X-50.0 Y-33.0 I3.0 J0.0
G1 F30.0 Z-6.0
G1 F300.0 X50.0
G3 X53.0 Y-30.0 I0.0 J3.0
G1 Y30.0
G3 X50.0 Y33.0 I-3.0 J0.0
G1 X-50.0
G3 X-53.0 Y30.0 I0.0 J-3.0
G1 Y-30.0
G3 X-50.0 Y-33.0 I3.0 J0.0
G1 F30.0 Z-7.0
G1 F300.0 X50.0
G3 X53.0 Y-30.0 I0.0 J3.0
G1 Y30.0
G3 X50.0 Y33.0 I-3.0 J0.0
G1 X-50.0
G3 X-53.0 Y30.0 I0.0 J-3.0
G1 Y-30.0
G3 X-50.0 Y-33.0 I3.0 J0.0
G1 F30.0 Z-8.0
G1 F300.0 X50.0
G3 X53.0 Y-30.0 I0.0 J3.0
G1 Y30.0
G3 X50.0 Y33.0 I-3.0 J0.0
G1 X-50.0
G3 X-53.0 Y30.0 I0.0 J-3.0
G1 Y-30.0
G3 X-50.0 Y-33.0 I3.0 J0.0
G1 F30.0 Z-9.0
G1 F300.0 X50.0
G3 X53.0 Y-30.0 I0.0 J3.0
G1 Y30.0
G3 X50.0 Y33.0 I-3.0 J0.0
G1 X-50.0
G3 X-53.0 Y30.0 I0.0 J-3.0
G1 Y-30.0
G3 X-50.0 Y-33.0 I3.0 J0.0
G1 F30.0 Z-10.0
G1 F300.0 X50.0
G3 X53.0 Y-30.0 I0.0 J3.0
G1 Y30.0
G3 X50.0 Y33.0 I-3.0 J0.0
G1 X-50.0
G3 X-53.0 Y30.0 I0.0 J-3.0
G1 Y-30.0
G3 X-50.0 Y-33.0 I3.0 J0.0
( Pocket1 )
S0
G0 Z1.5
G0 X1.6 Y0.0
G1 F30.0 Z-1.0
G2 F300.0 X-0.8 Y-1.3856 I-1.6 J0.0
G2 Y1.3856 I0.8 J1.3856
G2 X1.6 Y0.0 I0.8 J-1.3856
G1 F30.0 X4.0
G2 F300.0 X-2.0 Y-3.4641 I-4.0 J0.0
G2 Y3.4641 I2.0 J3.4641
G2 X4.0 Y0.0 I2.0 J-3.4641
G1 F30.0 X6.4
G2 F300.0 X-3.2 Y-5.5426 I-6.4 J0.0
G2 Y5.5426 I3.2 J5.5426
G2 X6.4 Y0.0 I3.2 J-5.5426
G1 F30.0 X8.8
G2 F300.0 X-4.4 Y-7.621 I-8.8 J0.0
G2 Y7.621 I4.4 J7.621
G2 X8.8 Y0.0 I4.4 J-7.621
G1 F30.0 X11.2
G2 F300.0 X-5.6 Y-9.6995 I-11.2 J0.0
G2 Y9.6995 I5.6 J9.6995
G2 X11.2 Y0.0 I5.6 J-9.6995
G1 F30.0 X13.6
G2 F300.0 X-6.8 Y-11.7779 I-13.6 J0.0
G2 Y11.7779 I6.8 J11.7779
G2 X13.6 Y0.0 I6.8 J-11.7779
G1 F30.0 X16.0
G2 F300.0 X-8.0 Y-13.8564 I-16.0 J0.0
G2 Y13.8564 I8.0 J13.8564
G2 X16.0 Y0.0 I8.0 J-13.8564
G0 Z1.5
G0 X1.6
G1 F30.0 Z-2.0
G2 F300.0 X-0.8 Y-1.3856 I-1.6 J0.0
G2 Y1.3856 I0.8 J1.3856
G2 X1.6 Y0.0 I0.8 J-1.3856
G1 F30.0 X4.0
G2 F300.0 X-2.0 Y-3.4641 I-4.0 J0.0
G2 Y3.4641 I2.0 J3.4641
G2 X4.0 Y0.0 I2.0 J-3.4641
G1 F30.0 X6.4
G2 F300.0 X-3.2 Y-5.5426 I-6.4 J0.0
G2 Y5.5426 I3.2 J5.5426
G2 X6.4 Y0.0 I3.2 J-5.5426
G1 F30.0 X8.8
G2 F300.0 X-4.4 Y-7.621 I-8.8 J0.0
G2 Y7.621 I4.4 J7.621
G2 X8.8 Y0.0 I4.4 J-7.621
G1 F30.0 X11.2
G2 F300.0 X-5.6 Y-9.6995 I-11.2 J0.0
G2 Y9.6995 I5.6 J9.6995
G2 X11.2 Y0.0 I5.6 J-9.6995
G1 F30.0 X13.6
G2 F300.0 X-6.8 Y-11.7779 I-13.6 J0.0
G2 Y11.7779 I6.8 J11.7779
G2 X13.6 Y0.0 I6.8 J-11.7779
G1 F30.0 X16.0
G2 F300.0 X-8.0 Y-13.8564 I-16.0 J0.0
G2 Y13.8564 I8.0 J13.8564
G2 X16.0 Y0.0 I8.0 J-13.8564
G0 Z1.5
G0 X1.6
G1 F30.0 Z-3.0
G2 F300.0 X-0.8 Y-1.3856 I-1.6 J0.0
G2 Y1.3856 I0.8 J1.3856
G2 X1.6 Y0.0 I0.8 J-1.3856
G1 F30.0 X4.0
G2 F300.0 X-2.0 Y-3.4641 I-4.0 J0.0
G2 Y3.4641 I2.0 J3.4641
G2 X4.0 Y0.0 I2.0 J-3.4641
G1 F30.0 X6.4
G2 F300.0 X-3.2 Y-5.5426 I-6.4 J0.0
G2 Y5.5426 I3.2 J5.5426
G2 X6.4 Y0.0 I3.2 J-5.5426
G1 F30.0 X8.8
G2 F300.0 X-4.4 Y-7.621 I-8.8 J0.0
G2 Y7.621 I4.4 J7.621
G2 X8.8 Y0.0 I4.4 J-7.621
G1 F30.0 X11.2
G2 F300.0 X-5.6 Y-9.6995 I-11.2 J0.0
G2 Y9.6995 I5.6 J9.6995
G2 X11.2 Y0.0 I5.6 J-9.6995
G1 F30.0 X13.6
G2 F300.0 X-6.8 Y-11.7779 I-13.6 J0.0
G2 Y11.7779 I6.8 J11.7779
G2 X13.6 Y0.0 I6.8 J-11.7779
G1 F30.0 X16.0
G2 F300.0 X-8.0 Y-13.8564 I-16.0 J0.0
G2 Y13.8564 I8.0 J13.8564
G2 X16.0 Y0.0 I8.0 J-13.8564
G0 Z1.5
G0 X1.6
G1 F30.0 Z-4.0
G2 F300.0 X-0.8 Y-1.3856 I-1.6 J0.0
G2 Y1.3856 I0.8 J1.3856
G2 X1.6 Y0.0 I0.8 J-1.3856
G1 F30.0 X4.0
G2 F300.0 X-2.0 Y-3.4641 I-4.0 J0.0
G2 Y3.4641 I2.0 J3.4641
G2 X4.0 Y0.0 I2.0 J-3.4641
G1 F30.0 X6.4
G2 F300.0 X-3.2 Y-5.5426 I-6.4 J0.0
G2 Y5.5426 I3.2 J5.5426
G2 X6.4 Y0.0 I3.2 J-5.5426
G1 F30.0 X8.8
G2 F300.0 X-4.4 Y-7.621 I-8.8 J0.0
G2 Y7.621 I4.4 J7.621
G2 X8.8 Y0.0 I4.4 J-7.621
G1 F30.0 X11.2
G2 F300.0 X-5.6 Y-9.6995 I-11.2 J0.0
G2 Y9.6995 I5.6 J9.6995
G2 X11.2 Y0.0 I5.6 J-9.6995
G1 F30.0 X13.6
G2 F300.0 X-6.8 Y-11.7779 I-13.6 J0.0
G2 Y11.7779 I6.8 J11.7779
G2 X13.6 Y0.0 I6.8 J-11.7779
G1 F30.0 X16.0
G2 F300.0 X-8.0 Y-13.8564 I-16.0 J0.0
G2 Y13.8564 I8.0 J13.8564
G2 X16.0 Y0.0 I8.0 J-13.8564
G0 Z1.5
G0 X1.6
G1 F30.0 Z-5.0
G2 F300.0 X-0.8 Y-1.3856 I-1.6 J0.0
G2 Y1.3856 I0.8 J1.3856
G2 X1.6 Y0.0 I0.8 J-1.3856
G1 F30.0 X4.0
G2 F300.0 X-2.0 Y-3.4641 I-4.0 J0.0
G2 Y3.4641 I2.0 J3.4641
G2 X4.0 Y0.0 I2.0 J-3.4641
G1 F30.0 X6.4
G2 F300.0 X-3.2 Y-5.5426 I-6.4 J0.0
G2 Y5.5426 I3.2 J5.5426
G2 X6.4 Y0.0 I3.2 J-5.5426
G1 F30.0 X8.8
G2 F300.0 X-4.4 Y-7.621 I-8.8 J0.0
G2 Y7.621 I4.4 J7.621
G2 X8.8 Y0.0 I4.4 J-7.621
G1 F30.0 X11.2
G2 F300.0 X-5.6 Y-9.6995 I-11.2 J0.0
G2 Y9.6995 I5.6 J9.6995
G2 X11.2 Y0.0 I5.6 J-9.6995
G1 F30.0 X13.6
G2 F300.0 X-6.8 Y-11.7779 I-13.6 J0.0
G2 Y11.7779 I6.8 J11.7779
G2 X13.6 Y0.0 I6.8 J-11.7779
G1 F30.0 X16.0
G2 F300.0 X-8.0 Y-13.8564 I-16.0 J0.0
G2 Y13.8564 I8.0 J13.8564
G2 X16.0 Y0.0 I8.0 J-13.8564
( Drill1 )
S0
G0 Z1.5
G0 X-23.5 Y23.5
G81 Z-10.0 R1.5 F30.0
G81 X-40.0 Y0.0 Z-10.0
G81 X-23.5 Y-23.5 Z-10.0
G81 X0.0 Y0.0 Z-10.0
G81 X23.5 Y23.5 Z-10.0
G81 X40.0 Y0.0 Z-10.0
G81 X23.5 Y-23.5 Z-10.0
G80
M5
M30
/code]

I had a quick look at your code and it looks fine, I think you may be loosing steps in the Y axis.

Graham

I checked the y axis by running a loop that returned y to o over 50cycles and it was fine! I don't think I am loosing steps. If i cut a rectangular pocket on x ,y its fine no problem but if i slew the pocket by say 10 deg i have the same problem with a stepped pocket as i did with the circle pocket in the original g code.
Thanks for your help.
Tony

Graham,

I've built a cnc quilting machine, that uses Mach3 to control it.  I need a way to reset the dro's to zero at the end of a pattern, and then restart at the same place, thereby extending/repeating the pattern, connected end to end.  Any ideas?

Larry

Use a G52 X? Y? to shift the datum the pitch of the pattern at the end of the run put a G52 X0 Y0 in the program

Put the pattern code in a sub program and just call it with a M98 Pnnnn

Graham

Graham,

I'll give that a try and see what happens.  I'll let you know what happens.

Larry

If you need some help with the format of the code just send me a PM.

Graham

Graham,

I tried the code that you recommended and unfortunately no joy.  The code would work if it were a milling machine, however, since it isn't, the quilter only recycles to the front of the pattern and starts over at the datum.  I have been fighting this issue for about 6 months now, and I know that there is a way to do it, I just can't find it.

Larry