i made most of the fixture this morning and everything worked just fine.  i was able to rough at various levels and came back to do a finish pass and the part came out great but a little small on the diameter.  so i decided to create a finishing cycle with my cam program (onecnc btw) and here is the code it spit out.  as far as i can tell the code is fine.  for some reason it will do the first rough at .250 deep, which is correct.  then it decides to plow into the material at the bottom of the hole to .800 deep.  well this just ruined the first hole in the fixture.  when i back the tool up and out and retouch it off, the tool is .300 lower than expected.  ok, no problem maybe the touch off was off, then i went and ran the first hole again.  it again wanted to plow to .800 deep.  pulled it out and retouched off the tool again...again .300 low.  rehomed the machine and retouched off the tool.  now its .600 high and retouched off to the exact first number i ahd before to within .0002. 

any idea whats going on here?  i find it strange that it ran everything else just fine and the first set of programs i ran on it. 


N90 G49
N100 G17 G40
N110 G49
N120 G17 G40
N130 G20
N140 G80
N150 G90
N160 G98
N170 (0.37INCH END MILL)
N180 T1 M06
N190 S950
N200 M08
N210 G43 H1 D1
N220 G00 X0.67 Y0.4875 Z0.5
N230 Z0.1
N240 G01 Z-0.25 F2.0 S950
N250 X0.867 Y0.4528 F4.0
N260 G03 X1.0987 Y0.615 R0.2
N270 X1.105 Y0.6875 R0.4175
N280 X0.27 Y0.6875 R0.4175
N290 X1.0987 Y0.615 R0.4175
N300 X1.1017 Y0.6497 R0.2
N310 X0.9364 Y0.8467 R0.2
N320 G01 X0.7395 Y0.8814
N330 Z0.1
N340 G00 Z0.5
N350 X0.67 Y0.4875
N360 Z-0.15
N370 G01 Z-0.5 F2.0
N380 X0.867 Y0.4528 F4.0
N390 G03 X1.0987 Y0.615 R0.2
N400 X1.105 Y0.6875 R0.4175
N410 X0.27 Y0.6875 R0.4175
N420 X1.0987 Y0.615 R0.4175
N430 X1.1017 Y0.6497 R0.2
N440 X0.9364 Y0.8467 R0.2
N450 G01 X0.7395 Y0.8814
N460 Z-0.15
N470 G00 Z0.5
N480 X0.67 Y0.4875
N490 Z-0.175
N500 G01 Z-0.525 F2.0
N510 X0.867 Y0.4528 F4.0
N520 G03 X1.0987 Y0.615 R0.2
N530 X1.105 Y0.6875 R0.4175
N540 X0.27 Y0.6875 R0.4175
N550 X1.0987 Y0.615 R0.4175
N560 X1.1017 Y0.6497 R0.2
N570 X0.9364 Y0.8467 R0.2
N580 G01 X0.7395 Y0.8814
N590 Z-0.175
N600 G00 Z0.5
N610 X0.6749 Y0.4866
N620 Z-0.175
N630 G01 Z-0.525 F2.0
N640 X0.8719 Y0.4519 F4.0
N650 G03 X1.1036 Y0.6141 R0.2
N660 X1.11 Y0.6875 R0.4225
N670 X0.265 Y0.6875 R0.4225
N680 X1.1036 Y0.6141 R0.4225
N690 X1.11 Y0.6875 R0.4225
N700 X0.4415 Y1.031 R0.4225
N710 X0.3579 Y0.8684 R0.2
N720 X0.3953 Y0.7519 R0.2
N730 G01 X0.5118 Y0.5893
N740 Z-0.175
N750 G00 Z0.5
N760 (END TOOL)
N770 M5
N780 M09
N790 M25
N800 M30
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The code - fed into my office machine, seems to descride a circle, with two sidings.

The program seems to start on one of the sidings, describe an arc to the main line, run round the circle, and then turn off down the second siding.
It repeats that 3 times.

On the fourth time it joins the main line, travels round the circle, but it goes too far and cuts a third siding in the opposite side of the circle. This is a new cut at 0.525 depth and the same feed, where you have used three feeds to get to this depth on the rest.

The error, if it is an error, seems to be at line 700.

Jim,

thanks for looking at this...  the code is supposed to plunge into the material (material is gone from previous cut) and then do a line move and then arc into the cut.  the cut is a circle that is 1.215 diameter and it is being made with a .370 end mill.  its supposed to rough the circle at a .250 depth and then rough at .500 and then .525 then do a finish pass at .525 depth at a larger diameter taking out the last .010 of material. 

Sounds like you may be loosing steps when doing a rapid in the Z+ direction, is that a possibilty? Try lowering your accel a bit for the Z motor tuning and see if it helps.
Hood

sorry i should have mentioned its  servo driven mill.

Have you tried single-stepping the program, to see exactly where it goes wrong?  I would guess you'll find one of the Z retracts doesn't work - perhaps the head is too heavy/too much friction for the axis motor to lift?

Regards,
Ray L.

What resolution are the encoders? what gearing if any? Ballscrew pitch? Servo drive make?
Hood

250 ppr encoders
nema 34 servo motor
gearing is 4:1
ball screw pitch is .200
gecko servo drives
72 volt power supply

like i said this is really baffling me.  i ran another program and it does just what i tell it.  i'm about to run the program that crashed here again and see if it does it again. 

Ok well its not likely losing position due to overloading, I was wondering if your reported error was within the 128 count error limits the Geckos have but thats obviously not the case.
 Are you using the parallel port or SmoothStepper?
Hood

parallel port.  it ran the first part of the program for 7.5 hrs straight with no problems and the z repeated to within +/-.001 on all the holes in the fixture.