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Mach4 General Discussion / 2.5 carving - Z stepper creeping upward

« on: October 01, 2017, 08:10:08 AM »

So my father and I designed and built our own 2' x 4' cnc router:

http://www.openbuilds.com/builds/warnke-cnc-router.4383

All seemed to be well until we began to try our hand at a complex relief carving:

http://www.openbuilds.com/threads/suggestions-to-streamline-my-router-motors.10184/#post-58655

We are seeing an issue in the z motor where it gradually loses position as it works its way through the carving.  It is creeping upward (not downward) and it is a gradual consistent position loss - about .005" loss of position in z (shift upward) per 16" by 1" of carved area.

Some pertinent specs on all of this:

We are generating g code using an stl in artcam.  G code looks fine.
We are using Mach 4 as our router software.  
We have the PMDX-424 for our motion controller

http://www.pmdx.com/PMDX-424

Here is what we purchased for motors drivers and power supplies (these exact ones from this site, tho we added 1 more set to our order as we have a dual driven y axis and we intend to add a rotary axis later; so 5 motors total):

https://www.omc-stepperonline.com/cnc-kit/4-axis-85ncm1204ozin-nema-34-stepper-motor-and-driver-and-power-supply-4-ma860h-34hs46.html

We have tried a lot of different parameter changes, switching voltage settings, slowing everything way down, etc and nothing seems to make a difference.  It's just not holding position in z when it cuts this relief carving.

We did a test cycle where we just moved the z motor straight  up and down in repetition a bunch for a prolonged period of time and it held position.  It only seems to lose position when carving stuff like this.

The coupling is not lose at all (we double set screwed each side to each shaft - plus that wouldn't account for consistent z position loss upward anyway).

We are running a windows 10 PC USB'd to our PMDX board.

At this point we pretty much figure the problem is either Mach 4, the pmdx motion controller or the motor driver...I guess it could be the computer or USB? I don't know.

To add to the frustration, after a week of running great (beside the position loss) now when you tell our VFD air cooled motor to turn off in Mach 4, it doesn't stop right away...it just keeps going and gradually slows down whenever it wants bit by bit (sometimes not at all and you have to turn power off)..

Neither of us are electricians or controls guys.  We are machinists and mechanical designers, but the controls stuff was a first try rookie effort so it's a little frustrating stumbling around this all.  We just want everything to work like we need it to.

Any ideas on what this could be?  

Does anyone else run Mach 4 with the PMDX?  Anyone else see these issues?  Position loss in z or spindle not turning off when you push the spindle off button in Mach 4? (Spindle on button is working fine).


Thanks for any help.  We keep trying things to no avail and we are starting to get discouraged  here!