I just finished rebuilding my 1612 mini CNC, properly repairing a snapped spindle bracket, removing the laser entirely (I have others) and re-doing some of the electrics.
I have a specific job in mind for this machine, and testing was going well, until I tried something new; using a big v-carve bit and, for the first time ever, running the spindle at less than 100% pwm.
End result is higlighted above, the spindle went well off course when asked for a 10x10mm box outline at 50% pwm.
I correlated this to PWM almost immediately; The perfect square cut next to it was done with the same bit, from the same startpoint, with 100% power. As were the other straight cuts there.
Simply running the spindle at 50% unloaded and un-moving let me see that all three axes were gently jittering and wandering (X worst of all), going back to full power stopped it completely.
My first work on this involved redoing some cable re-routing, shielding and twisting pairs for the 36v spindle lines, routing them away from the control lines. This made a noticeable improvement, but was no solution. I also saw an improvement when I bonded the machine chassis to ground, and from changing the PWM frequency.
The real solution came and adding proper supression capacitors to the spindle:
This is a common solution for brushed DC motor noise; 0.1ĀµF caps to the spindle body, and 2.2ĀµF across the terminals. These small ceramics are rated to 50v.
This machine has a totally open chassis and a unshielded control board (a very early esp32 control board, lots of long thin tracks etcā¦) so I guess my main surprise should be that I have not seen this happen earlierā¦
When reading up on what to do I noticed several people on the electronics forums saying that brushed dc motors are bad for noise, but pwm+brushed dc motors is really, really bad. Too many transients happening at once I guess.
And, eventually, I got what I wanted (text pathing courtesy of LaserWebās vpath feature), this is a test for something Iām working on.