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How do you prevent static charge from shop vac dust hood?

Discussion in 'CNC Mills/Routers' started by Rendermandan, Nov 28, 2016.

  1. Rendermandan

    Rendermandan Journeyman
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    I have had an issue in the past where all of a sudden my X axis would suddenly start moving twice as far and twice as fast as normal, usually ruining my cut (Wood). The only fix was to replace the driver on my Arduino conk shield.

    I have not had a problem recently and was working this weekend. I was going to cut some MDF which makes quite a bit of dust so I hooked up my shop vac to my dust hood and shortly after starting, my Z axis plunged down into my bed and crashed. I checked the controls and sure enough, it was moving twice as far and twice as fast just like the X axis did. Another blown Driver!

    I got to thinking that I have not hooked up my vacuum in a while and it was working fine. then as soon as I did it blows another driver? Maybe I'm getting some sort of static charge from the vacuum?

    Is there any way to prevent this?
     
  2. Joe Santarsiero

    Joe Santarsiero OB addict
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    You have to give the static a place to discharge other than through the machine. Grounding the hose is a good start. Copper desoldering braid works well and it's cheap. A few wraps around the hose and a connection to a ground should do it.
     
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  3. Rendermandan

    Rendermandan Journeyman
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    Thanks for the idea. I took some old lamp,wire and stripped the insulation off. Wrapped it around the end of the tube that connects to the dust hood. On the other end I left the insulation on and routed it back to my psu where I connected it to the green grounding wire. I have yet to test it out for fear I will blow another driver. I don't have any more at the moment.
     
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  4. Joe Santarsiero

    Joe Santarsiero OB addict
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    Haha. Well, if your blowing drivers as is what do you have to lose? ;) Run it. Btw, I like to leave a piece of the wire end in contact with the inside of the hose. Superstition maybe...
     
  5. Metalguru

    Metalguru Master
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    My 4" dust collection system came with a large roll of multi strand bare copper wire. You are supposed to spiral wrap it around any hoses or plastic pipe and ground it properly. I grounded mine by tying it to a standard 3 prong plug ground pin and leaving the other 2 pins unconnected.

    There have been many cases of static discharge starting fires or even explosions in dust collection systems. Shop vacs are particularly prone to this sort of thing since they are usually all plastic. My hair (all 3 of em') stands on end when I touch the vac after its been running for a while.
     
    #5 Metalguru, Dec 3, 2016
    Last edited: Dec 3, 2016
  6. JustinTime

    JustinTime Master
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    I just read recently (a few days ago) that that is not true. It has to be like a perfect storm to happen. It can happen but your chance to get hit by lightning is way greater.

    Mainly the spark has to be really strong, stronger than normally generated by our systems and the dust has to be very very fine, finer than the normal dust we have running through our system.
     
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  7. Metalguru

    Metalguru Master
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    This topic is hotly debated on the internet. There are a lot of articles extolling both sides of the argument.

    Essentially, I'd rather err on the side of caution. One less thing waiting to blow up in my shop is a bonus.:D
    Also, it's nice not to look like Albert Einstein and yelp loudly every time I touch my blast gates.:rolleyes:

    MG
     
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  8. Rendermandan

    Rendermandan Journeyman
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    I agree it might be an improbable situation, but not impossible. The issue I have is static discharge somehow making its way back to my controller and for god know what reason, changes the microstepping so it moves inappropriately. I have wrapped the last few feet of the hose with a grounding wire so hopefully I won't have any more drivers blowing.

    I am considering upgrading to the cnc xpro controller. Those drivers are not replaceable, so I don't want to upgrade and then have it blow the entire board...
     
  9. Metalguru

    Metalguru Master
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    I don't consider the CNC XPRO controller to be an "upgrade". Not to criticize their product, I just don't like the all in one boards in general because of the necessity to trash a high dollar board if you have a minor fault. As you said, if you blow a stepper channel on that, it's two Benjamins to fix it. If you blow a stepper driver board, it's an order of magnitude less to replace. As far as I'm concerned, your money would be much better spent on a good motion controller like an Ethernet Smooth Stepper or something similar and keep your current separate stepper drivers. Note that I have no particular brand loyalty, nor am I casting aspersions on particular manufacturers, these are just examples and my opinions only.

    I think chassis grounding is also very important and frequently neglected on these CNC machines. I always run a ground wire from one mounting screw on each axis motor (with star washer), and from the main base frame of the machine to a central grounding point (also with star washers on each connection) on my electronics chassis. This point is also physically wired to the power supply ground screw and the incoming power cord ground. This pretty much eliminates static buildup and also helps with electrical noise problems such as with limit switches false triggering, etc.

    You need one from each motor, because the axes are generally insulated by the wheels and have no way to drain off static charges, Also, just for general electrical safety, UL requires that your machine frame be grounded to the 3rd prong on the plug.

    MG
     
    #9 Metalguru, Dec 4, 2016
    Last edited: Dec 4, 2016
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