As you can hopefully see, the cube is not really a cube. The distance of one corner to an adjacent corner is ~ 19.5 mm and the distance from one side midpoint to the opposite side midpoint us 20.5 mm, the length of the cube is 19 mm.
What can I do to fix this or to narrow down, what the problem is?
More info: I cut this using a 3.175mm flatend using linkage mode.
Seems odd, if you don’t mind uploading your gcode? I know Luban’s CNC function is rather limited, but I wonder if it’s a limitation of how it just converts an STL into a heightmap and wraps it around your defined stock. Theoretically in linkage mode, it should do straight lines, as X comes across, so the curve is likely done in Luban.
Idea: Might that be caused by a wrong z-origin?
In my head it would make sense that I arrive at that shape if the bit is longer then the machine thinks it is.
If the z origin was incorrect, I believe you would expect to see a consistent offset in your carving which does not seem to be the case.
It could be backlash in the mounting of the CNC head, if you have too high a feed rate or too large a step down the cnc module may actually be moving in reaction to the cnc carving process.
What bit and settings did you use? Loading the the cnc file into Luban shows the curve in the preview, also what version of Luban did you use?
This is the end-view when previewed in Luban of your gcode:
I loaded up the model in Luban 4.1.3 and set it up, these are what I got, along with the settings used.
Edit: if you’re using the straight-groove v-bit, that sorta would explain it. If it’s running linkage mode, center will be wider since the bit Vs out, it can’t technically do a straight line, you’ll have to use some form of flat endmill. Especially since Luban can’t actually calculate bits properly.
I am sorry for the delay.
The first screenshot you posted shows that the last layer should be flat.
I used a 1/8" flat-end bit with very similar settings. Just with a stepdown of 2 insted of 12mm.
Those 12mm seem rather much for me, or does it actually work to go that deep?
I don’t understand why Luban generated that outer ring of small nudges for me, but not for you?
