Possible Z-Axis skipping in 3d milling?

[benjamd]

So I milled a lithophane last night, came out pretty good but I got one raised corner. Its clearly delineated and everything in that corner is raised. Any ideas what could be causing this?

The piece was milled first with a roughing pass using a 1/8th ball nose, then the finishing pass with a 1/16th ball nose. The finishing pass was made at a 45 degree angle so its clear this artifact came from this pass. I'm guessing the z-axis must have skipped coming back down at some point resulting in this offset? I have a fan blowing on my TinyG drivers, though I'm not sure how well thats working, my Z-axis motor does seem to get a little hot (I can touch it but its uncomfortable to hold my finger on it for too long) so perhaps this is the problem?

[cvoinescu]

You are almost certainly right, it looks like a few lost steps on the Z axis. The temperature of the motor should not cause it, and if the driver entered thermal shutdown, it's weird that it did that only once, and not all the time as I would have expected. In other words, I have no clue what could have caused you to lose steps.

[dataway]

I experienced a similar issue with my tinyG setup and loaded the latest EDGE build and it seemed to fix my issue with 3D Milling. I would recommend you try the latest edge build found here: http://synthetos.github.io if that does not resolve you issue I would post your inquiry to the tinyG forum : https://www.synthetos.com/forums/tinyg/tinyg-support/ The team on there is very good at resolving issues.

[benjamd]

Huh, I had not considered it being the TinyG firmware. I had an edge build from a month or so ago but I'll update again and see if its any better I know they were fiddling around with a lot of things over the last couple of months so its quite possible. I'll try that tomorrow, hopefully it will fix this last niggling issue. I was having z-axis problems before where the shaft had some play between the bearings so I took part my old Shapeoko V1 z-axis and modified it into something like the v2 axis (replaced the axis carriage plates with the new style, cut down the old motor mount plate to mount the spindle onto, flipped the rail around and rounded off the bottom plate on the rail for clearance). I then ground down a large washer to fit between the bearing plates and I think this has eliminated any movement on the shaft now. Hopefully I a firmware upgrade will fix this latest issue then I'll finally be able to reliably cut

[secretspy711]

had the same issue recently. dropping the Z acceleration from 25 to 20 mm/s/s did the trick for me.

[Gadgetman!]

I had a similar mess on my ShapeOko recently.
But on mine it was the collet not gripping the bit properly, so on some passes it wouldn't plunge properly, but instead push the bit more and more up into the collet.