Router bit going rogue

Hi all! I have assembled the MPCNC a year ago and have done some carvings with it. This one is a 3 feet diameter panel and I decided to carve it using a ball nose bit without facing the stock in a 3d parallel operation that, initially had the carving time of 16 hours. The problem happened after 6 hours of work.

The question is: what did I do wrong?
Is it a too long carving time for that bit? Did it overheated? Should I have faced and perhaps done an adaptive clearing before? Is 16 hours too much for the router/cnc/bit/my neighbours (noisy vacuum) :stuck_out_tongue_winking_eye:?

I have the time-lapse of the carving but I couldn’t upload in this post.

I have to redo the work so any suggestion is welcomed.

Hi that seems like a lot of material to clear… is the ball mill dull or sharp now?
Were there burnt marks on the wood? That can indicate a dull bit.
Another thing to check is if your drivers are getting too hot.
Also, if your stock was not parallel with the carriage you could wind up with a situation where it’s taking too big bites as it moves across if your ramp clearance height is not higher than the stock at that point.

I would have done adaptive clearing with a single flute upcut bit or roughing bit and leaving stock then a second pass with the ball mill but I’m no expert.

This was the first job for the bit. I suppose it was sharp before. I guess it is now darken because of the erratic path it took and instead of cutting 0.6mm it had to do its whole diameter. Or could it get dull just by cutting 0.6 mm slices for 6 hours? Is the darken colour an indication of dullness?

I just feel them with my finger like you are testing the sharpness of a chisel or blade… if the only burnt part is where it went off course it should be fine.

I bet it’s in the CAM. What speeds are you running? Especially the Z speeds…

My bet is this. It looks like it was cutting diagonally and the X axis cut out intermittently, causing segments straight in Y. Or it could also be wiring on the X axis but I think that’s a bit less likely.

Yeah that is what I am wondering too… also weird how the z axis drops so radically.

I have one of those $20 temperature guns I check my driver temps with.

On 3D carves, it is tricky for the CAM to respect Z speeds. Because it is trying to go a certain speed for the milling. So in this case, it is important to make sure the max Z speed in the firmware is small enough to avoid skipping steps. If it is trying to carve at 15mm/s and it hits a steep hill, it will be asking the Z to move 15mm/s. So you need Marlin to slow it down.

So here is the summary of the fix:

  • Face the stock
  • Adaptive clearing
  • Change the angle of the parallel operation to either horizontal or vertical but not diagonal
  • Provide better cooling for the drivers
  • Check the Z speed and limit it (to what?)

I had a prototype on construction foam and I didn’t like the marks it left after the adaptive clearing or the pocket clearing (fusion 360). So maybe I can run it one mm to the base of the cut and have the parallel operation to clean it. What you guys think?

What would be your approach to this project in terms of operations?

I have one of those. What temperature should be the threshold? I printed a case for it and the raspberry pi (octoprint) is separated. I’ll be adding fans to it before running again.

Few more questions about the fans. I printed the minion case from Thingiverse and it seems to be using 2 6mm fans. Which configuration they would be more efficient? Blowing air inside or outside? Or one bringing cool air inside and the second blowing hot air outside?
Is there any specific pin I could connect them or should I connect directly to the power pin (12v)?

Maybe implement a tool change and use some rougher endmill for rough material removal? It might lead to the need for z probing though, not sure…

From googling it sounds like > 100C is definitely bad. These days I have some small heatsinks attached to the drivers and I just feel with my fingers to make sure they are not too hot to touch.

If they are 12v fans you can just connect them to the 12v. Most boards also have an always on fan pin somewhere too.

IIRC correctly I remember reading somewhere the rambo has a lot of the heat conduct to the back of the board so you might want to make sure there is some air room or even airflow behind the board (if you are using the rambo)

It’s also possible to reduce the current on your drivers if they are getting too hot via a hardware pot or gcode command depending on the board. I don’t actually use any fans at all but my room temperature doesn’t get very warm.

@billsey has a good idea with checking the Z speeds… you can check by typing in gcode with the speed like G0 Z20 F1000 etc to manually zip the carriage around and see what F speed will cause it to lose steps.

Thank you all.

I made those changes. My router (DWP611) died when I was about to start the second operation after facing, the pocket clearing. I got new brushes and replaced them today. All good for tomorrow’s carving. Now I’m wondering if that could be the reason.