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I'm building a DIY CNC router. I'm running at a low RPM and only planning on cutting soft materials (wood and under, maybe a PCB).

I'm currently having problems with magnetic interference. When starting the spindle, hard end stops would trigger, and sometimes my controller (arduino) would become unresponsive. For now I've turned off hard end stops, while building the rest of the machine. I'd like to re-enable hard end stops though.

I'm planning on moving my controller further away, and potentially placing it in a metal box. For the end stops however, I'm not sure how to solve it in an as DIY way as possible.

I've got a couple of questions:

  1. How can I measure interference, and below what levels should I stay?
  2. Will it help to simply wrap aluminum foil around my wires and hook that up to ground?
  3. Does it work to hook up shielding to DC ground/zero, or should I hook it up to my AC ground in front of the AC/DC converter?
  4. Where can I find a "beginners guide to magnetic interference"?
Daniël van den Berg
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  • Start using a laptop with no charger. Define link all specs, h/w. s/w , full steps? Current limit? UART errors? CNC shield? GRBL code? End stop verified? Link YouTube video – Tony Stewart EE75 May 14 '21 at 17:31
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    how do you know that the problem is caused by magnetic interference? – jsotola May 14 '21 at 17:41
  • @TonyStewartEE75 Thanks for your input. I would be able to provide this information tomorrow, but the problem I'm having is that I can't find any "general" information on this subject. As such, I've tried formulating my questions so that they would help anybody running into similar problems. – Daniël van den Berg May 14 '21 at 18:47
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    @jsotola Now that you say so, I am not 100% sure. This is my assumption because moving the spindle away from the other wires seems to reduce the chance of it stalling. However, I still want to learn about magnetic interference and shield my systems from it, even if my current problems are not caused by it. – Daniël van den Berg May 14 '21 at 18:49
  • how are the end of travel switches wired? ... do they share ground or power paths with the motor? ... in other words, is the sensor ground connected at the motor, or is it connected directly at the main power supply, or somewhere in between? – jsotola May 14 '21 at 18:59
  • @jsotola it's connected to the CNC shield on the controller. The CNC shield and the motor do not share a common ground, but are connected to the same converter. – Daniël van den Berg May 14 '21 at 19:10
  • I’ve worked through similar problems with my CNC. In particular I’ve had issues with things freezing up when I start the coolant pumps, which are directly Driven from AC mains. Wrapping foil round cables may help a little for radiated emissions, but using screened cable is far better. I have some small SSRs that switch on zero-crossing and may help when I get round to fitting them. My spindle motor runs from a VFD and has never caused a problem, but the steppers that drive the axes have caused problems. A combination of screening the power and signal cables and cable routing has helped. – Frog May 14 '21 at 20:30
  • I ran 2m cables 12V 2A to 3 stepper motors without noise problems using laptop everything well grounded and shielded cables. I recommend GRBL Panel is the best software to drive GRBL code on an UNO to CNC shld. Used mechanical endStop switches, no issues for rezero auto-cal. – Tony Stewart EE75 May 15 '21 at 03:39

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the CNC shield and the motor do not share a common ground,

This is one of your problems. A common ground and shield wires for all power and signals is necessary to minimize EMI. A small RF cap help on endStop switches only if you get false signals with NO switches wired correctly.

But avoid multiple SMPS if you can help it as users seem to not know why they have interference. I.e. use a laptop on battery with 1 supply for all CNC for starters.

Reading Henry Ott’s latest book or an older version in Archive.org will take you a few months to learn or longer but well worth it.

I would say shorter if your search skills found my answers here on this site.

Tony Stewart EE75
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