Hi all,

new member here. Got myself a Sainsmart Genmitsu 3018 PROVer and am reasonably happy with it so far. Seems kinda rigid but does have some flex in it due to the thin guide rails on the X axis which are only 10mm diameter and the mount for the spindle being made of plastic.

I plan to upgrade the whole X and Z axis in one go and have sorted out a nice list of bits and pieces I need to buy. Surprisingly cheaper than I was expecting to be honest and using the Openbuilds components should make it easy to assemble and dial in.

I'm trying to mill PCBs and with some WD40 on the PCB and a German spiral engraving V-bit (0.1mm 30 degree) I'm getting nice clean cuts with a good Z accuracy (I'm running at 10k RPM and 30mm/min plunge and 60mm/min XY feed rate). The main problem I have with the machine is the runout I am getting on the spindle which is a cheap 44mm diameter 775 motor. I've measured the runout with a plunger gauge angled up into the bore of the collet chuck and I am getting 80 - 90 microns of runout in there. As I rotate the spindle the runout seems to be circular, not some nasty notchy runout. This means that if I want a 0.3mm track width in my PCBs I need to design the PCB with a 0.6mm/0.7mm track width or higher as the runout causes a lot more of the material to be milled away than should be. This is messing with my PCB designs and putting me in an existential funk.

Therefore, Is there any way to counteract runout on spindles? I'm thinking along the lines of shimming the motor in its mount. I'm having a hard time trying to visualise what I would need to do to correct for this problem. My thinking is that the inside of the ER11 collet extension isn't rotating on the vertical in the X and Y axis and therefore the end of the V-bit is rotating in a small circle. By shimming the motor with some shim stock or even just paper or aluminium foil can I correct for that?

Hopefully I will be rebuilding the X and Z axis in the near future to increase rigidity and therefore improve accuracy and allowing me to run at higher feed rates but it's gonna take me a couple of months to get all of the parts together and I'd like to sort out this problem sooner rather than later. Even if just for my own sanity. A new spindle will probably be high on my list of new parts to get. One with less than 0.01mm runout if possible and no ER11 collet extension. I'm beginning to dislike those cheap little poorly made things.

Thanks in advance for any advice or suggestions.

Cheers

NM