Static Electricity

Static Electricity

Postby Win Brayer » Tue Apr 08, 2014 8:04 am

I am having a real problem with Static Electricity in my work shop. Last session, accidentally touched clamp or bed and computer locked up and program quit running. Especially frustrating after several cuts and no way to get back to 0 point to redo and continue.
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Re: Static Electricity

Postby Adrian » Tue Apr 08, 2014 8:15 am

How have you got your machine grounded?

It varies from machine to machine but here's some info on recommendations on grounding a ShopBot for example - http://shopbottools.com/ShopBotDocs/fil ... 8%2007.pdf

For my machine I found that running a wire from one of the legs to a copper spike and through the dust collection hose was enough to sort out all static problems and the materials I cut 90% of the time are known for generating static.
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Re: Static Electricity

Postby ChrisInEstes » Tue Apr 08, 2014 6:04 pm

I had a nasty problem with static when I first got my CNC machine... Lots of ruined work... It took me a while to figure out what the issue was, so that added to the frustration. Finally I thought I should Earth Ground it, and that did the trick. I drilled a hole through my concrete floor, drove a 6' long copper ground rod in, and grounded the router chassis, control box, and spindle. Before I dove the 6' copper rod in, I took a look at the plans for the building to see if there might be anything under the the slab where I drove the rod.

I disconnected my dust collector from the CNC at the same time, too. Even though I had a grounded copper strap run through it, the humidity is so low here that I was getting visible static discharges. So yeah, it makes a mess, but I don't have any static problems anymore.

Hope this helps,
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Re: Static Electricity

Postby PaulRowntree » Tue Apr 08, 2014 6:12 pm

Chris, Adrian : you both recommend a true spike to ground. Is a solid strap to the electrical system's ground not enough? It is hard to imagine more than a few millivolts developing with a good strap. We have installed ground plates when working with RF generators, but high-frequency equipment is usually non-ohmic ...
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Re: Static Electricity

Postby Adrian » Tue Apr 08, 2014 7:05 pm

It's the same spike that the electricity supply grounds through so it's the same result in my case.
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Re: Static Electricity

Postby ChrisInEstes » Tue Apr 08, 2014 9:21 pm

I went with the spike so I could be sure about the Earth Ground... I don't know if it IS better, but it made me FEEL better. One day I may see about hooking dust extraction back in to the system.

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Re: Static Electricity

Postby GRANDPA » Tue Apr 08, 2014 10:32 pm

Earth ground and electrical system ground are not the same. Earthen ground is the 6 to 8 foot rod pounded into earth and is the true ground. This is the only true type. Make sure the copper wire is connected to bright metal on your CNC or dust collector and on the clamp as well on the rod. This is one continuous circuit (not water pipe or building steel) since those connections may have paint or sealers where connected and defeat the value.
Electrical system ground (third wire in plug, usually goes back to the neutral in the box and is not true ground unless that bar in the box is then connected to a rod - Earthen ground as described above . (this actually sometimes is called a floating ground and spikes from motors, lights and other equipment can create static discharge and float back thru GREEN wire.
Most houses and small shops do not have true earthen ground. this is an age old problem from early 1960's with large computers I had experience with.
Pound the rod, get good single strand copper and connect both the CNC and your dust collector, but on seperate wires or you defeat the ground and static from either will cause problems.
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Re: Static Electricity

Postby IslaWW » Wed Apr 09, 2014 12:25 am

There are a couple things to consider here.

First we are looking for a way to discharge static. Depending on the actual condition of the earth that the rod is driven in it may not provide the path of least resistance for the discharge. That resistance may allow the frame or equipment ground to spike voltage for a few milliseconds. Which may be interpreted by a control computer as a signal.

The second is ensuring that the ground potential of the machine is as close to the same as that of the computer that controls it. This will aid communication and substantially reduce communication errors that occur when they are different enough to "trick" the computer into thinking that a few tenths of a volt was in fact a bonafide signal. USB communication is particularly sensitive to this. Also sensitive are lower end systems that do not "pull up" inputs and require a signal that is pulled low to activate. This allows numerous false triggers to occur.

Most MFGR's and most code jurisdictions recommend (even require) connecting the electrical system ground to the machine frame. For the above reasons and safety. Most codes require a single point for grounding rods, even when multiple are used there is a min/max distance for them. In some cases, adding an earth ground rod can cause problems in computer controlled machines due to a change in the ground potential created.

There are many cases, such as Adrian's where adding a ground rod solved a problem. I might wonder if the machine frame was properly connected to the electrical system ground as is required in the US? In some cases the problem may be solved, but by not the method possible.
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Re: Static Electricity

Postby zeeway » Wed Apr 09, 2014 11:37 am

Certainly the best ground is connection to a long, conductive rod driven into normally damp ground, such as that near an external surface drain. (You can imagine that such a rod driven into desert sand may not be an effective ground...)

Having said that, it may be somewhat discouraging to a casual user to think that such a complex solution is necessary. I would start at the simple end of the scale:
1. Run a bare copper wire through your dust collection hose, and connect that to the metal frame of your machine at one end.
2. Make sure your control computer is using a common ground with your machine/control.
3. Make sure your machine is grounded to a ground lug of your electrical system ( not the neutral).
4. Make sure that your spindle (or router) is electrically grounded to the ground lug of your electrical system (two-wire plugs do not do this).

These are the steps that eliminated the electrical gremlins in my system

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Re: Static Electricity

Postby Larry Elliott » Sat Aug 16, 2014 3:38 pm

In looking for a solution to problems with static I found this thread. This had been an intermittent problem since I got my router in 2008. I thought it was properly grounded to the shop's electrical system, but from reading here it appears that I may need to add a ground rod closer to the machine as my meter base (ground rod) is nearly 80 feet away. Although my dust collector does have a ground wire through the ducts from machine ground to collector fan motor it trashed out a piece of 3/4" PVC yesterday and got me searching again as this problem usually only occurs in the winter when the humidity is lowest. For the past week or so every time I walked across the carpet in my office and touched something metal it give a pretty sharp bite like in the dead of winter. Living in the Mid-South the summers are normally warm and very humid but this year has been an exception, my humidity meter in the shop was reading at 28% yesterday when the machine started losing steps and was out by about a 1/16" for a while, that was not a big problem but it continued to lose steps and in a few minutes was too far off to pass our quality standards on our sign work. Thinking back, a job we routed last week had a small glitch that was most likely caused by static, so I thought that if humidity is the problem or lack thereof a good watering of the concrete floor would be all that is needed. I wet it down, let the nozzle spray a fine mist and placed a fan blowing across it, in about an hour the humidity was up to 55% and we completed the job in a new sheet of material without any problems. Raising the humidity did the trick this time, but I plan to rework my grounding from the ground up.
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Re: Static Electricity

Postby glenninvb » Sat Aug 16, 2014 4:40 pm

Larry,

Are you sure static is causing your present problem? From what I've seen, Dust collector static will cause a limit switch (mechanical) to trip. At first when I experienced that problem I upped the bounce setting and the problem went away, I then added a ground wire in the collector hose because I was getting tired of getting shocked.

I'm servo with well shielded cables, and I have no idea if static jumping to stepper wiring could cause lost steps? Are you sure your problem is not a mechanical binding issue?
If your collector ground wire is attached to a proper machine (fan unit) chassis earth ground, you shouldn't have a static problem.

I'll add, it could be noise from spindle or router affecting stepper signal, just not sure if static will affect the same way.
But just guessing, let us know what you find.
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Re: Static Electricity

Postby glenninvb » Sat Aug 16, 2014 6:40 pm

Larry,

I have to admit after rereading your post, static sounds pretty likely especially cutting 3/4" PVC. Maybe bite the bullet and install a ground rod near machine. If there is an exposed copper water pipe near the machine perhaps you could try that. Might want to check if Vac. system chassis has a proper earth ground if that's where your connected now.
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Re: Static Electricity

Postby Tree_climber4 » Tue Oct 23, 2018 6:16 am

SO.. I am in this process right now. My CNC Shark HD4, while plaining down some African Mahogany just the other day, quit recognizing the pendant at the control box. I tried not to freak out because my $4,000 machine just poop the bed on me. I waited until the next day to call Tech support. They decided with an over the phone analysis that a certain circuit board in my control box had burnt up, most likely to static electricity. I won't bash them too hard right now (trust me, their original solution was a slap in the face, more or less), because most folks are here looking for a solution or a way to prevent this from becoming an issue at all. Being that most of these folks who purchase these machines are not idiots, and generally are capable of fixing this issue...ESPECIALLY with just a little bit of guidance. After finding out that this problem had already arose and the neglect to provide the customers who purchased this machine said guidance (without having to ask for it); IE instructions on how to eliminate static electricity. Below is the attachment that Next Wave's tech support emailed me, to eliminate the problem. Now I know that these same exact answers have already been given by others on this thread. It just blows my mind that there was no effort to get this information out to the consumers who have already invested in this equipment.
Attachments
Grounding recommendations.pdf
yeep
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