Help! 3D carving mode problems

Hello ,

I am facing a rather peculiar issue. My cnc works flawlessly when profiling, pocketing, v-carving. When I try to make a 3d carving though i have a problem with the Z axis. The roughing path comes out fine but when I run the finishing path the Z axis gradually dives in the material as the project progresses. Needless to say that the preview in the CAM software comes out as it should correctly without any issues. I managed to make a couple of small 3d carvings throughout the 6 months I owe my CNCEST6040, but most of the times the project fails because of the z axis. Anyone who can chime in and point me to the right direction would be much appreciated.

I am running the machine via USB on a dedicated offline computer which runs windows 7 32 bit and Mach 3.

This sounds like what happens when the Z axis loses steps while trying to lift the head. It's probably doing it a little bit with the other types of cuts and you're not noticing them. But a 3D toolpath requires lots of little Z moves, and they're adding up. Try reducing the acceleration on the Z axis by about half, and see if that fixes the problem. You could also try reducing its velocity. If none of these things helps, you might think about counterweights or gas struts on the Z axis. Also, check the coupler, to make sure it's not coming loose, which can also cause your Z level to drop, and make sure your collet is really tight - spiral-flute tools can gradually pull themselves out if they're not.