CNC randmoly stops when using shop vac

Hi Guys,

I ran into an unexpected issue this weekend:
So far, the CNC didn’t have any electrical problem, if was running fine. Recently, I added a dust shoe, connected to a little vacuum cleaner.
It seems like the CNC and the vacuum cleaner don’t get along too much… Whenever milling something, the Arduino will lose connection or even shut down and/or restart, at totally random times. I did not find any pattern so far.
This actually blew one Arduino Mega, first the regulator fried, then a little resistor near the USB port. I replaced it thinking it would solve my problem, but apparently it doesn’t.
After a bit of Googleling, I found out that this problem is not unknown, and it is likely cause by a ground loop. But I didn’t find any solution, or at least I didn’t understand what I’m supposed to do to resolve this.

Does anyone knows what I should do?
Thanks a lot in advance for your help,

ground loops occur in cars too when you are running your phone as a music player and going from headphone out to aux in on the car stereo whilst trying to charge the phone of the car ring main (12v battery) which also powers the stereo.

Two ways round it in a car,

  1. buy a special headphone to aux in cable which has a capacitor (I think) in it.
  2. don’t have the loop at all by powering them both with separate sources. so in the car this means using a second battery.

Now I recognise your name from Endless sphere and Emax scooter stuff so I know you have a big battery you could use for either the vac or the cnc. Just a suggestion. Also running electronics from batteries tends to create less noise in the line than from the mains. This used to be true in the days of ADSL where signal to noise ratio could mean more or less bandwidth so some people were claiming that running their router (not the mpcnc) of a 12v battery gave them better download speeds.

I guess keep the battery topped up before you intend to use it, make sure you have enough capacity for the job and unplug it before you turn on the vac.

Sorry to jump on this thread but could not figure out how to start a new thread.
I have built my MPCNC and have been trying to 3d print on it but every time I tried the model comes out with layers that are easily detached from each matter what I did including auto bed leveling I still have this problem and cannot print out a solid model that is not fragile. can someone please help me.

If you go to the root of the forum, then choose the subforum you want, then scroll to the bottom of your screen, you’ll see the new post section there.

Print hotter. Make sure to measure the diameter of your filament in a few places, average it, and put that in your slicer software (I use slic3r).

Post a pic of the bottom of your first layer. That will tell us lots of things.

Same problem here, the CNC randomly stops. Trying my first cuts since building it but hardly can get a full cut object. MDF 4mm, Dremel 4000 high speed, feedrate 5 mm/s.
Took the original short blue usb cable, vac cleaner on another source, without vac cleaner, it doesn’t help.
If I run the gcode above the mdf, it doesn’t stop!

Are you sure it is an electrical issue? What are you rapid speeds and what version of software/post processor are you using?

here are the pictures can someone help please

@Ragai Pleaser start a new thread and answer all the questions in the sticky. There are so many things that can be wrong we need to start somewhere, and in it’s own thread.


Yes, it is indeed me :slight_smile:
It’s been a while since I haven’t been on endless-sphere… They are getting super strict with electric scooter here in Shanghai so I may have to give away my awesome machine… The end of an era…

Anyway, the suggestion to use the scooter battery to power the CNC is not a bad idea. Powering the shop vac would be too complicated since I would have to convert the 72V DC into 220V AC, but I would not be limited by the power of my battery since it can deliver 11 000 Watts continuous…

It coud be a temporary solution, but I really wish to find a proper way to fix these things.


The problem is electric, I fried the Mega two times and I don’t think it is affected much by the speed since I tried to turn the pot to go 500% speed and it didn’t make any difference.

I made a quick test yesterday evening and it turns out that I apparently have no problem if I use the SD card reader instead of connecting the CNC to the computer.

I will need to make more tests to be sure of that.

By the way, using the SD card also solved my mysterious issue of “heating failed, printer halted” I was getting in the end of any job. So I think this has to do maybe with a setup in Repetier, so not an issue of movement speeds.

If you can, put the vacuum on one circuit and the PC/Arduino on a different one. If you only have one circuit breaker for all outlets it’s tougher.

I can’t… unfortunately.
But I’ve read on some websites that it may actually be worse, because the voltage differencial between the two grounds will be even bigger.

I’ll make more tests using the SD card instead of direct USB method. It is not really ideal since I was planning on using Estlcam for driving the CNC using the tool probe feature, but it may be a temporary solution until someone comes with a fix…

This is interesting. I run. My shop vac on almost every cut. So far so good.

That is weird. My spindle, ramps, laptop, and shop vac are all powered off the same power strip. The dumb ass that wired my barn only put 1 (ONE!!) outlet in the shop. Pretty much any time the spindle is spinning, so is the shop vac. It’s currently as I type this been running for 13 and a half hours. Which reminds me, I need a quarter inch ball nosed endmill…


Are you sure it is an electrical issue? What are you rapid speeds and what version of software/post processor are you using?

Have all your adviced settings, newest Estlcam and Repetier Host, the ramps are yours so preflashed… But I think I have found it: Used an older (2009 + Windows 10) laptop and when changing to a more recent laptop it runs fine. I presume the USB-port was to slow or maybe the computer itself?


Had the exact same problem initially.
Every time I turned the vacuum on or off the cnc controller rebooted.
What solved it for me was to use the same atx power supply for the Arduino as well as the raspberry pi running it.
I think the problem was a ground difference between them + the fact I was using a simple 5v power supply for the pi while the atx power supply is better protected against power spikes.

Hope this helps…