ANY HELP?? - Z Axis dropping during file run

[signblaster56]

Ok, so here is what is happening: First off, information: I am running an older Digital Tool 903, 5' x 10' with Perske 7.5 spindle. Using WINCNC controller, setting up files in Aspire.
I generally haven't had many issues with this router, however, I was running the 3rd sheet of the same file that has a single level (3/8") background routed down with raised letters and border, pretty simple stuff. Like I said this was the 3rd sheet, so the first two had run with no issues, then on this one, the Z axis began dropping down through out the run, I didn't catch it until it hit my spoiler board, but you can see from the photos that with each pass it was dropping down approx 1/8" or so and more as it went along. I checked WINCNC after I stopped the machine which still said it was running at 3/8" deep, so my conclusion is that the Z axis was "stalling out" on up moves and then cutting lower each time it re-entered the material. But the picture that you see has no lifts on the z axis until it completes that section, so I am miffed.

Has anyone had a similar issue? what are the causes? fixes? I generally keep the bearing on the z axis greased up good, not sure what could be the cause. any help is appreciated. Thank you.






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[ger21]

Your Z axis stepper is probably losing steps during retracts.
Check the Z axis for any binding, and lubricate if needed.

[signblaster56]

Ger21 - That's what I originally thought, but like I said on the posted pictures, the Z axis did not make and retracts just a solid clear out path. I grease the main bearings, should I lube up the side of the Axis plate as well? That rides between 2 sets of smaller sealed bearings.

[awerby]

I think Ger's right - this sounds like lost steps. You've got a very heavy spindle, so you might be simply overpowering your Z axis stepper when it tries to lift it. As well as lubrication - and yes, lubricate everything that slides, although oil might be better than grease - try lowering the acceleration on Z and perhaps fitting some gas springs to help with the weight of that Perske.

[Jon.N.CNC]

Always worth checking the coupling for any slip.