I have a simple Gcode program that starts by lifting the bit to Z0.100 then spirals down to Z-35.00 (mm), returns to Z0.100 widens the circle then spirals down to Z-35.00, ect, three cuts at -35 then a couple on shallower ones.

I have used similar code on the machine without problems, and I have checked the machine for drive slipage, the bit is tightened in the collet, there is no physical binding of parts etc and can find no reason why, on each return to Z0.100 the cutter goes a mm or so higher, so by the end of the program the cuts are shallower than they should be by 3-4mm (but still shows Z0.100 on the display).

I was testing the cut in foam (I reduce the speed to 200 before cutting the real piece in Acrylic). I removed the foam and cut 'air' but it still lost the Z.

I will try another piece which did cut correctly before in the morning just to prove to myself that it usually does not do this.

Is there something in the code causing this or is there a bug in Mach3 or could there be something else I havn't thought of?

Nick

N5 (File Name = probebody inner on Friday, August 31, 2007)
N10 (Default Mill Post)
N15  G91.1
N20 G0 Z0.100
N25 G0 x0.000 Y0.000
N45  X13.8780  Y17.0000
N50  Z0.1000
N55 F300.00
N60 G2  X20.1780  Y17.0000  I3.1500  J0.0000  Z-2.5
N65  X13.8780  Y17.0000  I-3.1500  J0.0000 Z-5.0
N80 G2  X20.1780  Y17.0000  I3.1500  J0.0000  Z-7.5
N85  X13.8780  Y17.0000  I-3.1500  J0.0000 Z-10.0
N100 G2  X20.1780  Y17.0000  I3.1500  J0.0000 Z-12.5
N105  X13.8780  Y17.0000  I-3.1500  J0.0000 Z-15
N120 G2  X20.1780  Y17.0000  I3.1500  J0.0000 Z-17.5
N125  X13.8780  Y17.0000  I-3.1500  J0.0000 Z-20.0
N140 G2  X20.1780  Y17.0000  I3.1500  J0.0000 Z-22.5
N145  X13.8780  Y17.0000  I-3.1500  J0.0000 Z-25.0
N160 G2  X20.1780  Y17.0000  I3.1500  J0.0000 Z-27.5
N165  X13.8780  Y17.0000  I-3.1500  J0.0000 Z-30.0
N180 G2  X20.1780  Y17.0000  I3.1500  J0.0000 Z-32.5
N185  X13.8780  Y17.0000  I-3.1500  J0.0000 Z-35.0
N190 G2  X20.1780  Y17.0000  I3.1500  J0.0000 Z-35.0
N195  X13.8780  Y17.0000  I-3.1500  J0.0000 Z-35.0
N210 G0  Z0.1000
N215  X9.1507  Y17.0000
N230 G2  X24.9553  Y17.0000  I7.9023  J-0.0000 Z-2.5
N235  X9.1507  Y17.0000  I-7.9023  J0.0000 Z-5.0
N250 G2  X24.9553  Y17.0000  I7.9023  J-0.0000 Z-7.5
N255  X9.1507  Y17.0000  I-7.9023  J0.0000 Z-10.0
N270 G2  X24.9553  Y17.0000  I7.9023  J-0.0000 Z-12.5
N275  X9.1507  Y17.0000  I-7.9023  J0.0000 Z-15.0
N290 G2  X24.9553  Y17.0000  I7.9023  J-0.0000 Z-17.5
N295  X9.1507  Y17.0000  I-7.9023  J0.0000 Z-20.0
N310 G2  X24.9553  Y17.0000  I7.9023  J-0.0000 Z-22.5
N315  X9.1507  Y17.0000  I-7.9023  J0.0000 Z-25.0
N330 G2  X24.9553  Y17.0000  I7.9023  J-0.0000 Z-27.5
N335  X9.1507  Y17.0000  I-7.9023  J0.0000 Z-30.0
N350 G2  X24.9553  Y17.0000  I7.9023  J-0.0000 Z-32.5
N355  X9.1507  Y17.0000  I-7.9023  J0.0000 Z-35
N360 G2  X24.9553  Y17.0000  I7.9023  J-0.0000 Z-35.0
N365  X9.1507  Y17.0000  I-7.9023  J0.0000 Z-35.0
N380 G0  Z0.1000
N385  X4.6946  Y17.0000
N400 G2  X29.3614  Y17.0000  I12.3334  J-0.0000 z-2.5
N405  X4.6946  Y17.0000  I-12.3334  J0.0000 Z-5.0
N420 G2  X29.3614  Y17.0000  I12.3334  J-0.0000 Z-7.5
N425  X4.6946  Y17.0000  I-12.3334  J0.0000 Z-10.0
N440 G2  X29.3614  Y17.0000  I12.3334  J-0.0000 Z-12.5
N445  X4.6946  Y17.0000  I-12.3334  J0.0000 Z-15.0
N460 G2  X29.3614  Y17.0000  I12.3334  J-0.0000 Z-17.5
N465  X4.6946  Y17.0000  I-12.3334  J0.0000 Z-20.0
N480 G2  X29.3614  Y17.0000  I12.3334  J-0.0000 Z-22.5
N485  X4.6946  Y17.0000  I-12.3334  J0.0000 Z-25.0
N500 G2  X29.3614  Y17.0000  I12.3334  J-0.0000 Z-27.5
N505  X4.6946  Y17.0000  I-12.3334  J0.0000 Z-30.0
N520 G2  X29.3614  Y17.0000  I12.3334  J-0.0000 Z-32.5
N525  X4.6946  Y17.0000  I-12.3334  J0.0000 Z-35.0
N540 G2  X29.3614  Y17.0000  I12.3334  J-0.0000 Z-35.0
N545  X4.6946  Y17.0000  I-12.3334  J0.0000 Z-35.0
N550 G0  Z0.1000
N555 G0 X3.2089  Y17.0000
N570 G2  X30.8470  Y17.0000  I13.8190  J-0.0000 Z-2.5
N575  X3.2089  Y17.0000  I-13.8190  J0.0000  Z-5.0
N590 G2  X30.8470  Y17.0000  I13.8190  J-0.0000 Z-7.5
N595  X3.2089  Y17.0000  I-13.8190  J0.0000 Z-10.0
N610 G2  X30.8470  Y17.0000  I13.8190  J-0.0000 Z-12.5
N615  X3.2089  Y17.0000  I-13.8190  J0.0000  Z-15.0
N630 G2  X30.8470  Y17.0000  I13.8190  J-0.0000 Z-17.5
N635  X3.2089  Y17.0000  I-13.8190  J0.0000  Z-20.0
N650 G2  X30.8470  Y17.0000  I13.8190  J-0.0000 Z-22.5
N655  X3.2089  Y17.0000  I-13.8190  J0.0000 Z-25.0
N650 G2  X30.8470  Y17.0000  I13.8190  J-0.0000 Z-28.0
N652  X3.2089  Y17.0000  I-13.8190  J0.0000 Z-28.0
N654 G2  X30.8470  Y17.0000  I13.8190  J-0.0000 Z-28.0
N655 G0 Z0.1000
N665 G0 X0.0000  Y17.0000
N680 G2  X34.0000  Y17.0000  I17.0000  J-0.0000 Z-2.5
N685  X0.0000  Y17.0000  I-17.0000  J0.0000 Z-5.0
N700 G2  X34.0000  Y17.0000  I17.0000  J-0.0000 Z-7.5
N705  X0.0000  Y17.0000  I-17.0000  J0.0000 Z-10.0
N720 G2  X34.0000  Y17.0000  I17.0000  J-0.0000 Z-12.5
N725  X0.0000  Y17.0000  I-17.0000  J0.0000 Z-15.0
N740 G2  X34.0000  Y17.0000  I17.0000  J-0.0000 Z-17.5
N745  X0.0000  Y17.0000  I-17.0000  J0.0000 Z-18.0
N746 G2  X34.0000  Y17.0000  I17.0000  J-0.0000 Z-18.0
N747  X0.0000  Y17.0000  I-17.0000  J0.0000 Z-18.0
N750 G0  Z0.1000
N752 G0 X0 Y0
N755 M5
N760 M30

Hey Nick, sounds to me like you are skipping steps while feeding. Is this a stepper machine? Give it a program to rapid the Z up and down as in the program you have posted (without the spiral) and see if it still does this. Also, what are the motors tuned at? X Y and Z.

Brett

OK, I wrote a short program to go up and down and it proved that the machine is either loosing steps or has a drive slippage of some kind, the fact that it gets higher each time, I think, rules out drive slippage as that would occur on the transfer from going down to fast up, which would make it loose height, not gain it, so I will go with loosing steps at this stage.

The settings I have are below (figures in brackets show the proportion of the settings in relation to the X and Y settings which are more or less identical and seem to be working fine - *1/2 means the Z setting is half the x-y setting)

Steps per   804.837....  (*2)
Velocity mm/min 1005.6  (*1/2)
Acceleration  56.17  (*1/3)
G's  0.00572
Step pulse 1
Dir pulse 0

Program used
G0 Z0

F300 (set speed)
G1 Z-10 (go down slow)
G0 Z0 (go up fast)
G0 Z-10 (go down fast)
G0 Z0 (go up fast)

F300
G1 Z-20
G0 Z0
G0 Z-20
G0 Z0

F300
G1 Z-30
G0 Z0
G0 Z-30
G0 Z0

F300
G1 Z-40
G0 Z0
G0 Z-40
G0 Z0

etc to -80

The machine was returning to zero + a bit on all returns, obviously it was more apparent the further the travel

Nick

I don't understand why it would loose steps going down, and not up. Gravity is helping on the way down. Sounds like you have a mechanical slip. Have you checked your set screws in the motor, pullies, couplings? Not sure how it is set up, but I would look for a loose machanical connection. Can you post a picture of your z axis setup? Also might want to change your step and direction pulse time to 5.

Keep us posted.
Brett

Bret

Thanks for your time but I am embarrased to say I have found the problem, the drive coupling was slipping, I had recently checked it but it must have worked loose, I have stuck it with Loctite now, that should hold it.

Do you still think I should alter the step and direction pulse? If so will it alter the speed, distance, i.e. will I have to re calibrate it?

Nick

No problem Nick, and no need to be embarased. You'r not the first and won't be the last to et bit by that one. If your machine is running fine, I wouldn't worry about changing the step or direction pulse time. It won't hurt a thing if you do though, no adjusting after that either. I think I would bump them up, but that is me.

Brett