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Got Sparks (the Static Kind)?

Discussion in 'Grinders' started by dancom, Jun 5, 2017.

  1. dancom

    dancom Dust Maker Best Shop Tool

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    Following a conversation on FB late last week about getting static electric shocks from your belt grinder. Although it may seem hilarious when it happens to someone else, it's a pretty large safety thing in my mind. Nothing like getting a surprising jolt while you have a knife in your hand; standing in front of a moving belt.

    Also, I noticed a lot of people misunderstanding what is happening. There seems to be this misconception that the sparks are cause by the electrical power supply to the machine. The machine is not grounded properly and so on. In order to enlighten the hill billies I put together some graphics.

    With a belt grinder the charge accumulates on the belt as it's moving and some of this charge is transferred to you the operator. As you are likely not wearing bare feet in the workshop your body charges up like a static electricity battery. As a part of your body gets close to the metal grinder frame or other grounded equipment that snappy blue spark and familiar jolt gets you.


    [​IMG]

    That guy sure looks unhappy. Okay, so that's a really elementary way of describing it, but what can we do about it? We can try a few things.


    Spray your belts
    Many knifemakers use anti-static spray on the backs of their belts. Apparently this lasts the life of the belt. Sprays that are for fabrics and clothing like Static Guard work.

    Static Dissipation Brush
    Another option and the one I use is a small brush with brass bristles to remove the charge from the belt before it builds up on your human body.


    [​IMG]

    In the image we see the charge in red is being taken to the grinder frame and the operator looks much happier.

    The Brush
    This little project costs only a few bucks. The bill of materials is all shown in the image below.



    [​IMG]



    You need a brass parts cleaning brush. These are often sold alongside welding supplies at hardware stores. Don't worry if the handle is plastic, they all are nowadays. The second thing you need is 1" machine screw and mating nut. Finally a small L bracket. The bracket you could easily make your own if you like, but I had one handy.

    Cut the brush part off where the head meets the handle. It will be about 1.5 (40 mm) inches long after cutting it. Drill a hole right through the head of the brush and into the area where the bristles are. The hole needs to be a little bit bigger then the screw. Push the screw into the bristles and out the back side.

    Important: the screw must touch the bristles to carry the charge to the bracket and on to the grinder frame.


    Attach the bracket to the head and we're done the brush. Now to mount it somewhere.


    Locating the Brush
    Now we need to find an appropriate place to attach our brush to the grinder. One key thing is the brush doesn't actually touch the belt. It is placed very close to the belt, but doesn't drag on the belt.

    Some things to look for with placement are:

    The bristles should be close 1/16" to 1/8" (2 mm or 3 mm) from the back of the belt.

    Select a place where the where the belt doesn't move up and down too much, so avoid the tracking arm if that is on a spring. I put mine near the drive wheel on the grinder frame. On my BG-272 I have included a welded on 1/4" bolt specifically for installing the brush.

    I ideally the brush is placed near where you contact the belt, but that's not always practical. Any kind of intentional dissipation is better than none.

    Although the graphic says "NEW", this one's been in use since 2014.

    [​IMG]

    Hope this helps you be safer when grinding.

    Cheers,

    Dan
     
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  2. parker

    parker Active Member

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    :roflmao thanks for the info and the bit of humor
     
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  3. John Noon

    John Noon Well-Known Member

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    I know I am holding the knife wrong when I get zapped, some days more than others
     
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  4. Kwesi

    Kwesi New Member

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    Good safety info. Thank you.
     
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  5. dancom

    dancom Dust Maker Best Shop Tool

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    My absolutely worst moment with static electricity...

    I working in an electronics R&D lab where we once used a large cylinder of C02 for shock-cooling electronics in the environmental chamber. We'd blast C02 directly into the chamber which took it from room temperature to -60°C in less than a minute. I was holding the valve knob controlling the flow as we cranked the CO2 in through a rubber hose to the inside. As I peered into the observation window and a flash of 4" blue spark leapt from my forehead to the chamber's steel exterior. My co-workers thought it was funny...I had to lie down for a while. The incident report stated "severe static shock to head", actually does sound kind of funny. To remedy this we slung a chain over the tank and wired the chain to the test panel ground.

    Dan
     
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  6. Kwesi

    Kwesi New Member

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    Dan,

    You are very lucky guy to survive that with no brain injuries....... I now know where you got your super powers from :).
     
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