z axis inconsistency

[papakelly]

I've been running a fairly simple design which is a trace of a bitmap image (picture of my dog) and some font below. When I run the gcode file (I have a Shapeoko and am using Carbide Motion to run gcode file), I find the v-carve bit shallows out at different points in the job. I've run the file 3 times and found that the bit lifts so that it is barely tracing, and its happened at different points in the job.

My waste board is flat, the stock is even 5/8" thickness.

The bit always get shallower at points in the job, and it seems to have happened at different times.

Is there an offset setting or something I am missing?

Thoughts?

[garylmast]

I just had the same thing happen on some material I just ran through the planer, so I assumed the material was consistent in thickness. Turns out it wasn't. A good way to check is to set the Z height at a point on the material then with the spindle/router OFF, run it back and forth at different points. Another case I had a few hours ago, was the mill wasn't very tight and it slipped down slightly. At least that's a couple of things to check.

Gary

[John Jockusch]

I am running the exact same setup a Shaeoko XXL with carbide motion. I had issues with my waste board being flat (the board was machined to a specific thickness and my table was level), however; the gantry rales were slightly off causing the right side of my waste board being higher than the left. The difference was extremely minimal and not an issue when running profile cuts, but when I started doing v-carve inlays the difference made it imposable to get a perfect fit. Your waste board may be flat but did you run a clearing tool path to make sure it is the same height across the machine in relation to your gantry? I also had an issue running the travel speed to fast causing a slight flex in the gantry, this resulted in some areas being cut at different heights. As Gary said you could also have issues with the material you are cutting not being planned and perfectly flat (planers also need to be calibrated) or the bit slipping.