hello,

it's been several weeks now that i'm trying to solve this problem:

When i'm doing 3d finishing passes (Parallel Finishing from Rhinocam) at the moment when the Z axis retracts after finishing one part and before transfering to the next. The z-axis 'grinds' and i'm losing steps so the Z0 is not at the same height anymore and therefter the tool digs in deeper than it should making the parts useless.

Here's what i tried until now:

  • bought a power conditioner
  • reinstalled Windows from scratch on an SSD and optimised it
  • upgraded Mach3 to the latest version
  • cleaned and greased the z-axis parts
  • tripple-checked and tried out all possible and imaginable settings/combinations in Mach3 and Rhinocam
  • changed the Step and Dir lengths
  • inverted the Step and Dir low/high active
  • read all related threads in various forums and tried out any remotely related suggestions
  • edited the Gcodes to insert a G4 Dwell before the problematic retract movement
  • tried with or without Rapid movement
  • tried adding a radial exit of the toolpath before retract
  • tried all possible and imaginable combinations of speed/velocity



I think the PC is not at fault, Mach3 driver test shows 'System Excellent' for all kernel speeds including 100kHz

I also think it's not a speed/acceleration problem since i tried out everything from speed: 100mm/min to 3500mm/min with Acceleration of 10-2500mm/sec2

the problem persits, here is a video of it (with a 10sec G04 just before the problematic retract): Untitled Document

in this video you see the Z go up at 200mm/min .. when i test in motor tuning or jog i can get up to 2000mm/min without any problems and really smooth and speedy motion, even when i'm operation all 3 axes at the same time

most related forum threads i found pointed towards a speed/acceleration problem that's why i spent several days testing out all possible combinations. the problem is always the same, always only on the Z and always when retracting after a parallel finishing.

what's really strange is that the finishing pass itself runs without any problems, even at 2500mm/min, it's only the retract that blocks ... in the specs of the machine the max speed is quoted as 4500mm/min .. i tried everything .. slow speed, slow acceleration, slow speed, fast acceleration, fast speed slow acceleration, fast with fast and at least a hundred setings combinations in between

what's even stranger is that a horizontal roughing pass where there is much more radical movement and alsop a lot of Z retracts, it runs without any problems .. even at 2000mm/min


from what a friend who is an expert in mechatronics the machine itself is in good mechanical condition .. and he also can't figure out whats wrong

the machine is a Gravograph VX2 connected via an octocupler to the parallel port of a pretty high-end (for the time) IBM Thinkcentre. I'm using the original motors and onboard drivers and the machine has done me good service for almost 2 years now. I've tried opening up old GCodes which i know did not exhibit this problem (since i managed to finish the products without problems) and the problem is also present in those files which used to run fine

i'm really completely lost .. possibly more than the steps on my Z