Static electricity, how to fight it?

[Dragonfly]

Well, I had suspicions but today I am already sure there is a problem with static electric charges between the machine, the dust extractor, the PC and ... my own body.
I've had a few cases when a normal work goes to the scrap (and some valuable mills too) when suddenly a motor stops moving under conditions when the load is not high and the speed below the half of what the router is capable of.
Today I wanted to mill a simple ring out of 12 mm thick material which is called HPL (High Pressure Laminate). It is basically a stack of paper (maybe some powdered filler too) bonded with thermally cured resign and used for decorative tiles in buildings - exterior and interior. It resembles very much a material used widely in the past in the electric industry which we call here 'getinax' (obviously the name has come from a trade mark). Very good insulator.
I have a MDF sacrificial board, HPL over it and it cuts producing fine dust carried by a strong air flow along a plastic hose from a vac. Ideal for building static electric charges.
I have also an own made remote control pendant acting like a second USB keyboard to the PC.
After the job has started I saw that I can increase the speed some more and reached for the pendant and got a quite tangible electric discharge into my fingers. Simultaneously the motion went out of control and I lost some time pressing the reset (with nothing happening) on the pendant before it dawned to me to hit the big red button. As a result my beloved mill for fine cutting of fiber composites (2.4 mm dia) passed away heroically cutting about 4 cm at an unbearable depth.  
Nothing else suffered terminal consequences. The pendant it appears has lost the link with the PC. Unplugging and plugging again into the USB port restored its function. With regard to the motors my conclusion is that the discharge 'blinded' the drivers' input or the BOB. The BOB is fully optically insulated, no common ground or power between the PC and the router. Which is not a barrier for a high voltage discharge. The floor is covered with linoleum, I am standing in thick rubber sole shoes.
I guess I need some grounding but can't decide how to do it. IMHO the strongest source is the dust hose with fast moving air and particles rubbing onto it.

I know some of you use MDF/other dielectric boards too and some have wooden (or other dielectric material) machines.
Have you experienced static electricity build ups and discharges? And if yes what preventive measures you take?

[EddyCurrent]

The metalwork of your machine will be earthed surely ?
This is what we used in the print industry, just connect it to a good earth point.
http://www.epakelectronics.com/uvps_curingcontrols_antistatictinsel.htm
http://www.takk.com/takk-static-control-products.html#generators
There's this type of idea; http://www.axminster.co.uk/dust-extraction-system-grounding-kit
http://www.electroguardpaint.com/

[dh42]

Hello,

same for me, the dust pipe in PVC with wood chips that rub on the internal surface due to the air flow cause very height charge .. and very unpleasant !!   (I see a flash when I touch the tube with hand)

If the tube or the hoses hit a motor, the motor stop.

I've added a cooper wire wrapped around the hoses and connected to the earth to solve the problem.
(all the CNC frame is connected to the earth, and also the motors, but apparently, it's not sufficient)

The same pb can appears if the little flexible shielded hoses of the µ-lub are too close of the Z motor (especially if they do a loop), the motor can lose steps .. (and there is no static charge in the hoses ...). One time, this hoses are wrapped around the motor, because I've removed the hoses fixture to redo it, and after 3min all the machine won't move (the 3 motors) ... and the LED of the controller are totally mad .. I remove the hoses and everything started working again.

++
David

[EddyCurrent]

More reading.
http://forum.vectric.com/viewtopic.php?f=2&t=19627
http://www.cnczone.com/forums/safety-zone/2845-static-electricity.html
http://www.camheads.org/showthread.php?t=3800
http://www.sawmillcreek.org/showthread.php?139620-how-to-control-static-electricity-on-sheetstock
http://buildyourtools.com/phpBB3/viewtopic.php?f=9&t=586

[Bubba]

Some people run copper wire either thru vacuum hose/pipe or wrap outside to help with static electricity. I don't, because so far have no issues with static or electrical problems. All my wires are shielded type, and one side only is connected to machine frame to stop ground loop..

[Imagining]

As Bubba indicated...but a few more details.

Wrap the outside of the dust collection hose or PVC with an insulated copper wire and connect to the metal body of the dust collector.  Also, run a bare solid copper wire on the inside of the dust collection hose or PVC, though the cyclone or separator if you have one, and then attach this to the metal body of the dust collector.  Then connect from the dust collector to a copper rod in the earth.

If you use a shop vac with a plastic body, run everything to the copper rod.

You might also check the continuity of the ground on everything, machine, spindle, BOB, power supply, computer, fuse or breaker panel, electrical outlets, light switches, extension cords, and cords of the dust collector or shop vac.

If static electricity has not been a problem in the past, but is now a problem, something in the wiring on the machine, spindle, dust collector or shop vac, BOB, power supply, computer, wiring, outlet or switches has changed.

Odd as these may sound:  What kind of clothing were you wearing?  Some types of material in clothing generate static electricity.  Also, what was temperature and humidity level in the shop?

Have you tried wearing a grounding wrist band?

I am a wood worker [on occasion cut plastics] and have never have static electricity problems with the usual woodworking power tools or with my CNC.  My shops have had bare or painted concrete floors and painted plywood floors.

[Dragonfly]

Thank you all for the input! The beauty of this forum is that people here are willing to help and have experience in many areas.

Eddy, I have a considerable experience with printing - had my own design and pre-press small business for 15 years and because I took all the effort to provide the final printed product I have a lot of days (and nights) spent around the printing machines in print shops looking into their internals when serviced or prepared for a run. One of my thoughts was actually using the principle there to make some kind of metal brushes to equalize potentials between the material and the table.
Nothing has been changed on and around the machine. As I said I had some previous events with occasional weak discharge into a finger which I considered may be a cause for misbehavior.
It was today with a large thick sheet of that material on the table when the static electric potential became high enough. I suppose it forms a kind of big capacitor with the dust adapter plastic foil fringes brushing it. I have machined the same material before but not large pieces and while writing this it dawns to me that this one has a gray metal paint finish. A classic capacitor.

Tomorrow I'll try to electrically neutralize the hose and provide a wire from it to the cyclone body which is sheet metal and the metal frame of the router.
The problem here, as I see it ATM, is not power or mains earthing, it is the accumulation of high voltage static electric charges due to rubbing between the hose and the air/chips  mixture stream. And it depends on the properties of the material being milled.

[Jeff_Birt]

Insulated wire is next to useless for static dissipation and running a wire on the inside of the hose is just asking for a clog. The static charge is a difference in potential between the inside of the hose and outside of the hose. Take a bare copper wire and loop it through the hose about every 12"-18", I create a 'stitch' around a hose rib and then dab some black silicone RTV on the holes to seal them up. If you have a solid PVC pipe then run a screw into the pipe from the outside and wrap the bare copper wire around it. The screw needs to be just long enough to penetrate the pipe. This stitching down the side of the hose keeps the inside and outside at the same potential and when you connect one end of it to an earth ground (same earth as your electrical system) it will bleed off any charge that tries to build up.

[Dragonfly]

Yes, I forgot to mention that insulated wire won't do.
I have some length of braid (stripped off shielding) and was thinking about using it.
Or segmentate the flexible hose and connect the segments with thin metal tube (also have a suitable piece. Although this will increase clogging probability.

[dave benson]

FLY
I don't know if is any help in your situation, But are you  aware that there are many types of
Anti-Static Tubing around made in a variety of materials for different environments.
It is used extensively in the textile industry, And from personal experience, I know it works.
Just google Anti-Static Tubing.
Dave

[dh42]

The problem here, as I see it ATM, is not power or mains earthing, it is the accumulation of high voltage static electric charges due to rubbing between the hose and the air/chips  mixture stream. And it depends on the properties of the material being milled.

Yes, I agree. On my CN #2, I've replaced the PVC noze (close to the tool) by an alu noze, and it solves the problem even if the rest of the hose is plastic ... I don't understand why .. (maybe air speed, the noze is smaller diameter than the hose)

The static charge seems also to be dependent off the wood ; no problem with walnut but hight charge with maple ...  

++
David

[EddyCurrent]

Low humidity also increases the risk of static.

[lloydsp]

Military munitions plants keep the RH above 20%, typically running 25-30%, depending upon the moisture-sensitivity of the materials they're working.

Below 17.5%, casual handling of non-conductive materials will generate significant static.  Above 20, it's not much of a problem, except for special cases where the equivalent of a Van de Graaff generator is formed by moving parts of a machine (like a conveyor belt across two non-bonded rollers.  Of course, bonding everything is required to prevent just that scenario.

Lloyd

[Imagining]

Jeff Birt stated:  Take a bare copper wire and loop it through the hose about every 12"-18", I create a 'stitch' around a hose rib and then dab some black silicone RTV on the holes to seal them up.

Leave it to Jeff to come up with something elegant; which is why I bought items from him to finish my second CNC.


My suggestions are based on what I have seen shops and read in woodworking magazines   ...  must be all that sawdust clogging something.

[Dragonfly]

Well, the thread produced valuable info and advice for me and I hope not only me. Thank you all again.
I have a positive result but to be definitely positive on it I'll see what happens in the following days with different jobs.
Anyway right now I cut the part without a glitch touching the machine while working and moving the pendant here and there.
First, yesterday I noticed that the Y (my longest) axis motor is the one who fails brutally. And there's a logical explanation - its case was not electrically connected to the metal chassis, it has a metal mounting plate but the plate stands on plastic distancers. So I ran a wire from the plate to the chassis.
Second I wrapped a bare wire woven braid around the suction hose with loops around it at regular intervals, one end attached to the metal body of the cyclone. On the other side I replaced the short PVC tube with a metal one and attached the braid to it.
All parts having a galvanic link I ran a wire to the central heating pipe (the heating is not functioning). I am not in a workshop but a room and no convenient way to run a ground pole. Note that the router is powered from a transformer and the highest voltage is 32V DC. The spindle is powered by a separate cable with thick rubber insulation.
Third I discovered that due to a small error of mine in the PCB design for a LED indicator panel the DC negative was actually connected to the chassis which is not correct because I run separate negative wires to a common 'star' point.
That's my report for now.
Thanks again for the help.