Fusion CAM question

[chillybo]

Hello, could anyone explain why I'm getting these marks on my work pieces. I have a DIY build router. CS Labs IP/M controller. DMA680 stepper drivers. Use Mach 3. Use Fusion 360 hobby use.
I selected a pocket tool path for this part. In stock settings I added 5 mm additional stock to + and - on one axis. I'm sure there's something I don't know about in tool path settings /options or something to do with the CAM side. Thanks in advance.[

ATTACH]32572[/ATTACH]v

Sent from my CPH2305 using Tapatalk

[Muzzer]

Hard to be certain on the info provided but my first thought would be backlash and flex in the mechanical system, rather than CAM setup.

Backlash tends to be most obvious where the axes change direction ie at the extents of X and Y movement on the part. A picture of the whole finished part might provide more clues.

Are you using climb or conventional milling? Climb milling is often the default in the CAM for CNC machines but lighter machines with less rigidity and more backlash are best suited to conventional milling.

Some CNC machine controllers allow a degree of backlash compensation but that's really not the right way to fix lost mechanical movement, which is very nonlinear.

To get an idea of your backlash, tighten up the gibs a bit (to simulate the force due to the tool pushing against the workpiece) and move the table to the same coordinate position, approaching it from one side, then repeating the approach to the same commanded position from the other direction. Using a test indicator, you can measure the difference in actual position, which would ideally be zero but can never be so on a real machine. Youtube warriors like to do this with no applied load but in real life conditions, you will have some form of force resisting the movement.

The backlash results are often depressingly poor but unless you understand the root cause(s), you won't be able to fix it. This could be in the ballscrew, the ballscrew thrust bearings, the toothed belt pulleys (if you have them) or loose gibs etc.

[chillybo]

Thanks for this. I think you are correct. My Z axis was near the limit of its travel and the steel used for the part is gauge plate.
The part is pretty much similar on both ends. The machine didn't seem to have a problem ramping the holes out. The mark is where the end mill first makes contact to cut the fillet at the end of the piece (only at one of the four corners). This all fits with your explanation.
I can live with the defect in the part. I need to cut more of the parts so I may raise the stock higher so the Z axis has less flex.
Thanks.

Sent from my CPH2305 using Tapatalk