I doubt that it is V Carve related. It’s probably a mechanical problem of some kind.
Some possibilities:
- Slop in the Z axis. With the machine on (and the spindle off), is there any play if you try to move the Z axis up and down by hand?
- Work piece flex. As you remove more of the pocket, the remaining part of the workpiece may become more flexible. With upcut or downcut forces, the material may be lifting as you cut.
- Warpage. As you remove material, the remaining material may warp from internal stresses, affecting the cut.
Some possible fixes:
- Better work holding. In particular, for larger stock you may need to have ‘internal’ work holding, e.g. double sided tape or vaccuum holding.
- Finish passes. Having a final pass on the pocket that has a small DOC can help even things out. You can fiddle with the pocket DOC to leave a small amount on the last pass.
For example, lets say wou want a pocket that’s 3mm deep, and you have a DOC of 1mm. You get three passes, all full depth.
Set the pocket depth instead to 3.1mm. Now you get 4 passes, but the last one is very shallow. If cutting forces are the problem, they will be minimized on the last pass. If warping is the problem, taking off just 0.1mm is unlikely to cause very much more warpage.
Or, if the depth should be a particular value, fiddle the the per-pass DOC. Changing from 1mm to 0.95mm per pass gives 4 passes, the last one 0.15mm.
The downside of course is that it takes longer.
If your piece is still on the machine, you could try changing the pocket cut to give a shallow final cut and run that. Set the Start Depth to the current Depth, and increase the Depth slightly. For example, if your pocket was Start Depth 0, final Depth 3mm, then change that to Start Depth 3mm, final Depth 3.1mm.
What is the Depth per Pass for the Pocket operation?
How does that relate to the Max Depth?
One thing which I’ve found helps is to adjust the former in consideration of the latter — consider for example a Depth per Pass of 0.125" and a Max Depth of 0.5" — this results in four full-depth passes, but if one reduces the Depth per Pass to 0.124", then five passes are made, the additional pass removing only 0.004" of thickness, effectively a finishing pass.
Export the gcode and confirm the data is as expected. At least it will tell what it’s not.
I have seen this same behavior on my SO4, have not been able to figure it out. I also see strange pocketing path decisions like leaving a tall island in the middle of the pocket and finishing that last instead of going center out.
Maximum depth is .125
Set to take off .05 per pass
0.05 divides pretty neatly into 0.125:
0.125 / 0.05 == 2.5
So two full-depth passes and a third removing half as much.
If you instead use a Depth per Pass of 0.041" you’ll get four passes and the last will remove a very thin 0.002" of material.
I am doing a 1/8" cut so i changed it to .41 and it tuned out perfect. Thank you very much.