What causes these lines to happen?

I’m doing a 3d carve on plywood and I’m experiencing an issue where i get these straight lines randomly that sit proud above the surrounding area. This photo (white part) shows a flat part of the carving. These bumped out lines form a rectangle across the whole carving and occur on the other areas of the carving regardless of whether it’s flat or not. Sometimes the lines occur once, sometimes in groups. I reran the program, and the lines didn’t pop up in the same place but in different areas.

Machine is elite foreman with qcw and legs. 3hp spindle. Offset style finishing pass, starting from center.

Any idea what it could be?

Wood moves, deviation in model, weak clamps… could be several things

Your machine might need a bit of Tramming. If it is slightly off one edge of the bit can carve a bit deeper than its counterpart hence causing lines in each pass. There are many threads on the forum on how to Tram your router but I would guess looking at this its just a bit off.


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Cusps from the Stepover being to large, maybe?

E.g 3d finishing passes with a ball nose bit need to be as low as 8-10%

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Thanks for the responses and suggestions. @AndyP, yeah, the stepover is large on this. It is a rough ‘finish’ cut just to test how it will look on some test material so I run the stepover pretty large (like 20%). I wasn’t sure if you were referring to the small lines, but the issue is with these fairly large bumped out lines. This was done with a ball nose bit with a wide stepover, so the smaller lines aren’t too surprising to me. It’s not perfect, but I’ve checked the tramming of the machine to where it’s “good enough” for me, so when I run it at 7% stepover for a real finish cut, I don’t see any small lines.

The odd thing about these lines are that not only are they random, but they’re rectangular, narrow (but wider than 1 stepover distance), and they bump out quite a bit (sometimes as much as 0.05"). I’ve looked at the model, toolpaths in vcarve, and the gcode and there isn’t any unexpected rise in z for these areas. I ran the same program a second time over the same piece of wood dropping the work Z zero 0.05", and the lines appeared in different locations.

They look consistent and uniform along their lengths, even though they appear at random locations along the surface (left to right in your photo).

Kind of makes it hard to believe it’s tramming or stepover. Even wood movement, I’d expect not to see the lines so perfect (what are the odds the wood moves ONLY before the cut starts?) - same goes for something like bit slippage. You’ve also already ruled out the gcode instructions, so IMO, it’s still a mystery.

Have you searched the Masso forum?

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If it were a laser I’d swear it was skipping a line or jumping a tooth on a drive belt. Perhaps something similar here where Masso is injecting a line skip (or doubling up a move command). It’s like it skipped that “line” entirely in the motion control.

I haven’t searched the Masso forum yet. Probably should also contact their tech support to see what they think.

I’ve been reading search results via Google for months but finally joined yesterday - there’s invaluable information in that group that’s applicable to any CNC running Masso, so you get contributions from all over, not just users of one specific supplier. Highly recommended.