X2 tool entry cuts edge of pocket

[paulpounds]

Hi All,

I'm pretty new to CNC milling and I've just been put in charge of a Light Machines (now Intellitek) LMC-1000 3-axis desktop mill. I am producing toolpaths in Mastercam X2, post-processing them and run them on a PC with driver software for the LMC machine without too much trouble.

When milling a pocket, the tool will sometimes descend into a cut diagonally rather than vertically, taking chunks of the pocket wall with it. When I verify the program in X2, it shows vertical plunge approach for all cuts, but when I test with the LMC driver software it clearly predicts the diagonal tool collision.

What's strange is that the LMC software predicts collisions for only some pockets, but not other (virtually identical) geometry. I'm probably doing something wrong... but what?

I should note that in some cases I'm making a pocket in the base of an existing pocket. Could the problem be that it's ignoring previously cut geometry?

My pocket parameters are:
Tool: 0.125 flat end mill
Feed rate: 6.160896
Plunge rate: 6.160896
Retract rate: 20

pocket type: standard
retract: 2
feed plane: 2
top of stock and depth varies depending on depth of pocket
depth cut: 0.05

constant overlap spiral, 75% stepover
Helical entry turned off.

Can anyone tell me if the pocket-within-a-pocket is the problem, and how to resolve it?

[paulpounds]

I've solved it - it was to do with the way I was making my depth cuts. By trying to convince the CAM software that the top of the pocket island was 'top of stock' it bypassed all the sensible don't-run-into-things stuff that Mastercam does.

The correct way to machine geometry like this is to include the multi-depth sections in my selection and choose "use island depths" in the depth cuts dialog.

Tally ho!