static shock

There have been several threads about the static discharges from grinders on cold and dry days.

The buildup is in you. As your knife blade rubs against the belt, it loses electrons. Since you are connected to the knife, the missing electrons are replaced with ones from you. Normally new ones would come from the earth (ground) and replace them. When it is cold and dry, that is not as fast and easy, so you become positively charged. When there is a path for the differential to neutralize to ground ( moving your hand near the grinder frame), a bolt of electrons jumps from the grinder frame to you to replace the missing ones. Lightning is the same thing, just many million times stronger. A Van DeGraaff generator works exactly like your knife and the belt.

Using a proper ground strap is not dangerous. All you need is a 1 megohm resistor in the line. An alligator clip, a piece of stranded wire, a 1 meg resistor, and a short piece of light weight chain will take care of the problem safely and completely.

This has nothing to do with a bad ground on the motor, or shorts, or wiring.

Stacy
 
If bladsmith is correct, and the buildup is in you, you can also buy a "heelstrap" that fits on your shoe. It's just a strap that connects you to ground. A small string goes inside your shoe to make contact with you. You don't even have to put it in your sock - there's enough humidity in your shoe that it will work between your sock and shoe. Heelstraps get in the way a lot less than a wrist strap.
 
Like some have said:

Grounding the grinder chassis will not help (I tried it). The electric charge is on you, not the grinder.

Grounding yourself will help (I tried it).
 
We used to use heel strips in the Blue Room (ATC room), but I have found that on concrete floors they don't always carry away the charge .An anti-static floor mat would help, but a simple ground strap of some sort will take care of the problem. I'll have to get some shoe strips from a surgeon friend and try them to see how they do in the shop.
BTW, I put a magnet on the end of my ground strap, so it pulls off the metal it is stuck to if I walk away. I hook it to a piece of gear behind me.

The biggest problem with the sprays is that I change belts many ,many times on a single grinding day.

Back in the day ( I love when that term really applies) when the Blue Room was filled with analog CRT radar scopes and black lights for illumination, the rooms were kept at very cold temperatures to keep the equipment cool. The static buildup was insane. You could walk across the room and send a 2" bolt of mini-lightning to a desk. We used to come in with a fluorescent light tube and it would glow as you walked with it. Anyone who wasn't well grounded got shocked every time they moved.
I was involved with the conversion of the old system to the TPX-42 system and OD-58T new digitally converted image scopes (mid 70's). The first time I showed an ATC that he didn't have to put yellow dots on his screen to track an airplane, and that he could push some buttons and know the altitude and heading of any plane on his scope, he almost kissed me. Today an ATC can work on a laptop computer.
Stacy
 
Timely thread. I had arcs jumping from the grinder's tool rest to my 'organic' tool rest all morning. Just toughed it out mostly, but I have little red burns all 'round my belly button. Glad I'm not about 10"" taller. :D

Rob!
 
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