Electric shock from belt sanders

E

ErikMB

Joined
Jul 27, 2017
Messages
727
I keep getting electric shocks when I touch metal on both of my belt sanders, including when I turn them off. It's a bit painful but mostly it makes me jump when I am trying to be careful and precise resulting in mistakes on my projects.

Does anyone know what causes this? And how to stop it? Grounding problem with the electrical outlet? Static build up?

Solve with rubber shoes? I'm at a loss.
 
Well if you aren't getting shocked when you touch other conductive items in the room it's probably not static electricity.
 
I "work" outside, plugged in to an external house outlet.

Can't really call this awesome hobby "work" now, can I...?
 
I had that happen when I first started and used a 1x30. I’ve heard people (and I did the first time I used my 2x72) have that issue with steel platens. I added a ceramic platen and haven’t had that issue since.
 
Sorry, I'm being D-U-M dumb, but what's a platen? Is that the flat "plate" set at a specific angle, upon which we rest whatever we are belt sanding? Thanks.
 
Not grounded properly. Just run a cable from the chassis to the closest water pipe.
 
The issue of static build-up is common. It is worse in dry and cool climates, and really bad with a glass platen.
In the winter (low humidity and lower temperatures), most of us have to deal with it. Grounding the chassis of the grinder to a good earth ground (metal water pipe or ground rod) will usually take care of it. If the shop wiring is correct, this is already done by the power cord from the grinder and the wires coming from the breaker panel. Making sure the grinder is plugged into a properly wired and grounded outlet or cord is important for safety reasons.

In the case of static electricity, it is you that needs to be grounded. A ground strap from your shoes works well (search heel ground straps on Amazon/ebay) or a wrist ground strap ( search wrist ground strap) will allow the static to discharge and not build up.
An easy ground for knifemakers is a waist strap. Take a 36-48" piece of very flexible thin wire (20 gauge stranded wire is good), or use costume jewelry chain, and put an alligator clip on one end and a small piece of copper (1x3" is good) on the other. Stick the metal in your waistband or pants pocket and clip the other end on the grinder chassis. Technically, you should put a 1 megaohm resistor in the wire at the alligator clip end, but that really isn't necessary for a knife grinder situation.

Nerd stuff:
When the belt goes round and round your grinder, it pulls electrons from the earth and deposits them into you. You are wearing rubber soled shoes and standing on dry cement. There is no easy path for the electrons to get back to the earth. Thus, they build up a charge in you. This can become as high as 75,000 electron volts, but usually discharges around 10,000 EV. You reach out to the grinder or get your hand b]near the metal while grinding and ZAP! a tiny lightning bolt jumps the gap from you to the earth.
 
Stacy E. Apelt - Bladesmith said:
The issue of static build-up is common. It is worse in dry and cool climates, and really bad with a glass platen.
In the winter (low humidity and lower temperatures), most of us have to deal with it. Grounding the chassis of the grinder to a good earth ground (metal water pipe or ground rod) will usually take care of it. If the shop wiring is correct, this is already done by the power cord from the grinder and the wires coming from the breaker panel. Making sure the grinder is plugged into a properly wired and grounded outlet or cord is important for safety reasons.

In the case of static electricity, it is you that needs to be grounded. A ground strap from your shoes works well (search heel ground straps on Amazon/ebay) or a wrist ground strap ( search wrist ground strap) will allow the static to discharge and not build up.
An easy ground for knifemakers is a waist strap. Take a 36-48" piece of very flexible thin wire (20 gauge stranded wire is good), or use costume jewelry chain, and put an alligator clip on one end and a small piece of copper (1x3" is good) on the other. Stick the metal in your waistband or pants pocket and clip the other end on the grinder chassis. Technically, you should put a 1 megaohm resistor in the wire at the alligator clip end, but that really isn't necessary for a knife grinder situation.

Nerd stuff:
When the belt goes round and round your grinder, it pulls electrons from the earth and deposits them into you. You are wearing rubber soled shoes and standing on dry cement. There is no easy path for the electrons to get back to the earth. Thus, they build up a charge in you. This can become as high as 75,000 electron volts, but usually discharges around 10,000 EV. You reach out to the grinder or get your hand b]near the metal while grinding and ZAP! a tiny lightning bolt jumps the gap from you to the earth.
Click to expand...
You are WONDERFUL!!!!! Thanks for the explanation!
 
ErikMB said:
I keep getting electric shocks when I touch metal on both of my belt sanders, including when I turn them off. It's a bit painful but mostly it makes me jump
Click to expand...
It's VERY important to determine for sure if this is simple static electricity, OR if the wiring is screwed up. Do you get this shock by touching metal grinder BEFORE turning the grinder on, or ONLY after doing some grinding? AND, does it continue to shock each time you touch? OR, after first shock, does it shock again if touched before grinding more? If only first touch is a shock after grinding, then it's static so no big deal. The only danger is you'll hurt yourself jumping away.

If a shock happens before turning grinder on, and continues to shock each time you touch that is dangerous and the electrical wiring NEEDS to be checked ASAP.
 
Thanks, Ken.

The shock happens only sometimes and while running the machines. It does not happen all the time. Sometimes I get one shock, sometimes I get another one later, sometimes nothing.

For the 4", it only seems to happen when using the felt polisher. It gets a little worse when I use some polishing compound.

For the 1", there is no telling when or if it will happen.

I never get a shock when the machines are plugged in and off (or not plugged in).
 
Sounds like static for sure. While grounding everything works, sometimes just spraying the inside of the grinding belts with anti-static fabric softener or the wife's anti-static spray works just fine.
 
Static Guard spray on the back of the belt and rubber wheels will often eliminate the problem, but will need to be redone frequently. What is in a can of static Guard is deionized water and alcohol. It creates a high humidity zone around the fabric that allows the static to dissipate. A misting bottle of clean water and alcohol would do just as good and be almost free.

In industry, they also us static "collectors". This is a grounding device that looks like a brass or copper brush which hangs just shy of touching a moving belt or other static creating device. The static discharges to the brush instead of people around the belt. If you made one for a belt grinder it would go from the frame and hang about 1.5 to 2mm above the inside of the belt. A piece of thin copper or brass sheet would do fine. Of course, the grinder would need to be properly grounded.
 
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Stacy E. Apelt - Bladesmith said:
Static Guard spray on the back of the belt and rubber wheels will often eliminate the problem, but will need to be redone frequently. What is in a can of static Guard is deionized water and alcohol. It creates a high humidity zone around the fabric that allows the static to dissipate. A misting bottle of clean water and alcohol would do just as good and be almost free.

In industry, they also us static "collectors". This is a grounding device that looks like a brass or copper brush which hangs just shy of touching a moving belt or other static creating device. The static discharges to the brush instead of people around the belt. If you made one for a belt grinder it would go from the frame and hang about 1.5 to 2mm above the inside of the belt. A piece of thin copper or brass sheet would do fine. Of course, the grinder would need to be properly grounded.
Click to expand...
There is an article on Dan Comeau's website that illustrates one way to do what Stacy describes.
 
I am experiencing this really bad now, especially when it's cold and dry in the shop (garage) and I am using the glass platen. If I wet grind, I don't get zapped. Grinding on rubber wheels, nada. My VFD also goes into OCH (Over Current Protection) mode when it happens and shuts down, too. I checked all of the wiring and it's good, just started happening in the last 2 weeks when it got much colder out. If I run a heater in the shop and the temp warms up, it doesn't happen.
 
have you tried the brass brush gizmo?
 
Not yet, gotta try that next time I am in there! I just saw this post this morning.
 
I'm gonna try it, too. Those little shocks are f-ing dangerous.
I wonder if it's more of an issue for those who do their grinding without a tool rest?
 
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