Question on CNC dust collection - Router Forums
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post #1 of 8 (permalink) Old 04-03-2020, 08:50 AM Thread Starter
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Default Question on CNC dust collection

For those with dust collection/dust shoe setups on your CNC router what provisions - if any - have been made to bleed off any static electricity charge?

In operation, I don't notice any charge buildup on my vacuum hose when it is attached to my shoe but if I am holding the hose in my hand instead there is definitely a buildup of charge. My concern is that the same sort of charge is accumulating (unnoticed) when using the shoe.

My thought was to ground the hose attachment point on the shoe to the electrical outlet (earth ground) but perhaps there is a better way.

To give some background on why I am concerned: I once was sanding drywall with a RO sander with a shop vac attached. Static charge was always a problem (since it wanted to discharge through me if it could - ouch) but somehow the charge built up to the point where it arced through the insulation system in the sander to the neutral of the power line - to the point where the sander actually caught on fire. I don't expect anything that extreme to occur with my CNC but I am concerned that the charge could upset toolpaths etc.

Comments would be appreciated.
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post #2 of 8 (permalink) Old 04-03-2020, 09:04 AM
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The motor and frame of the dust collector should be grounded, so you can usually just ground it to the fan shroud. If the machine is all metal, ground it at the machine end as well.
Most just run a copper wire through the hose.
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post #3 of 8 (permalink) Old 04-03-2020, 10:40 AM
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Quote:
Originally Posted by ger21 View Post
Most just run a copper wire through the hose.
I just accept it and get shocked a couple times a day. It doesn't hurt too bad. 🙂
I've got a big roll of electric fence wire. It's not copper but should work. Sounds like a good Corona project.
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post #4 of 8 (permalink) Old 04-03-2020, 10:51 AM
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Attach the ground at the DC, not at the dust shoe.

My 4" clear hose has the wire running spiral embedded in the plastic and I have the wire grounded at the DC; there's not been an issue with static since doing that. Running a copper wire inside the hose and PVC would be better but I did it this way to see how it worked over two years ago and it's been fine for me - ymmv.

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post #5 of 8 (permalink) Old 04-03-2020, 11:07 AM Thread Starter
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I know from my investigation that the CNC router (frame,spindle, SM's) is NOT electrically connected to the line voltage neutral. The grounds being "extended" out to the router are PS grounds associated with the step motors and the spindle. So YES, you do not want to divert any static charge to that path or risk fatal damage to you PS's and VFD, etc.

My problem is that typically I use a std. shop vac to collect from the CNC and - since it is all plastic and the outlet plug does not have a ground connection - there is no ground path to discharge any static (the same scenario as my sander that caught on fire). So somehow I need to add an "auxillary" connection to earth ground. I have an idea on how I might do it but I thought perhaps others have already been down this path.

I suppose if you were using an air-cooled router with direct 120V connection to the wall outlet this would not be a problem.

Thanks for your comments.
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post #6 of 8 (permalink) Old 04-04-2020, 10:33 PM
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That static build-up is one of the common problems with the CNC Sharks and the cause of many missed steps. It might be due to all of the plastic used in their manufacture, I think the plastic helps store the static. I actually taped a fine florist wire to the plastic on my Z axis, pointed straight up so I could see how much shutter I was getting while cutting and that also seems to be bleeding the static off of the system. I realized the static was gone and removed the wire to see if it came back and the static returned. I put the wire back and no longer have problems with static. It might be discharging to the dust collector hose close to it.

Sometimes the discharge will take place when the on-off switch of a vacuum is used like when cutting without a dust shoe and switching the vac on and off to clean up lose chips intermittently. When that happens a noticeable misalignment of the cut path will be seen, maybe deeper, shallower, or jump to one side or the other.

The copper wire through the hose works and can be grounded to an outlet or better would be to install a ground rod outside the shop with the wire running to it.
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post #7 of 8 (permalink) Old 04-05-2020, 08:32 AM Thread Starter
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Mike, your experiences with tool path corruption are what I'm trying to avoid.

What I ended up doing is adding a sheet metal screw through the tip of the vacuum hose and then wiring that to the earth ground at a nearby outlet. The end of the hose seemed to be where the static was building up (based upon the amount of debris that collected there) and adding the ground point has taken care of it.
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post #8 of 8 (permalink) Old 04-06-2020, 01:05 AM
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I have a Shapeoko and on the Carbide 3d community forum newbies are always asking why my job stopped half way through. I live in east Texas where it is very high humidity. It is hard to raise a spark but it is possible. On the forum people recommend running a wire from the DC to the dust boot to ground the static to keep EMI from stopping the USB connection and loss of position on the axis. If you life in a dry climate or in a frozen one with low humidity you have to take static serious. Many of the newer dust collection hoses are made of conductive material and as someone else above said most have a wire that runs through them and you could use that and attach a wire to that to ground on both ends.
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