Help ! Major static !

[hiwa]

In my cement floor garage, I have my sharpening area. When I am sharpening knives on my !" Delta sander, I get a major static shock after evry pass of the blade. Humidity is 60-70 % and I am wearing running shoes. Does this ever happen to anyone doing the same thing? Any suggestions?

Thanks.

 

[dalee100]

Hi,

A very common phenomena. I've seen static charge buildups in industrial settings that were enough to knock you on your backside.

The proper way to stop it is to dangle some copper "tinsel" on the back side if the belt. The other end was run to a simple ground. You can approximate this by taking some fine stranded copper wire, stripping one end and fraying it out. Put it contact with the back side of your belt and ground the other end. This will bleed off any charge build up.

You can also put down a rubber mat to stand on. Though this can still allow some shocks on occasion. Say if you where to touch the grinder and the metal bench it was sitting on.

Your choice,
dalee

 

[hiwa]

I'll try the rubber mat thing 1st. If it doesn't help, then the copper wire trick.
Maybe the ground could be my anvil on the floor ?

 

[Jason B.]

Is the spark coming from the belt or the grinder body?

 

[hiwa]

Grnder body. At the end of my pass when my index finger is near the frame of the machine......a good zap !

 

[thombrogan]

I've gotten that one a lot, especially when using silicon carbide belts. Sanding in the middle of the work area between the top wheel and the tool rest at the bottom helps a lot, but the added control of sharpening near the top wheel is too hard to resist even with the shocks.

 

[gary jp4]

This can be serious given that it makes you jump and you are holding a sharp object next to a moving belt. 1/2" plus sparks are not uncommon with 1-2" ones possible. That's a big spark.

I have a Delta also. It can happen with any belt sander though, as well as blast equipment (sand blaster glass bead blaster, shot peen, etc). It only happens here in Tennessee in the winter when the humidity is low. It is worse with the leather belts for me. Some folks may never experience this in places where it is always humid.

I don't know about hanging tinsel on the machine, but for a Van de Graaff generator that is how you generate the static. The static charge is building up on your body. The way I understand it the belt takes + electrons from the machine frame which is grounded and deposits them on you through the knife. Anyway, standing on a rubber mat makes it worse. I have tried it. Standing on my bare concrete basement floor with bare feet stops it completely, but I don't recommend that. It is cold in your bare feet in the winter and if you lost the internal ground on the machine and it became charged with 120v house current you might get a more serious shock because you are grounded to the floor and the machine wouldn't be grounded anymore.

Grounding yourself to the machine will prevent the sparks. You can lean against the machine allowing you skin to touch the metal while you work and prevent the static build up, but that is not very convenient. Sharpening against the platen helps if you are touching the steel part of the knife because the spark will jump from the knife to the steel platen or at least wont have as far to jump even if you hand is closer because you or the knife are always closer to the platen then when sharpening on a slack belt. It doesn't hurt as much if it doesn't build up as much. The bigger the gap it needs to jump the higher the voltage will build up. All these things help prevent the build up of static electricity. I run a wire attached to the metal frame of the Delta with an alligator clip on the other end and attach it to my shirt sleeve allowing it to touch my wrist (in the winter). If it doesn't always touch skin a spark will build up but it is not as bad as the 1-2" sparks that can build without the wire and it only tickles.

There are grounding bracelets available for working with computer chips that would work even better if attached to the machine on the other end. Then you, the machine, and ground would stay evenly charged.

Gary

 

[THG]

Anyway, standing on a rubber mat makes it worse. I have tried it.

Definitely. If you stand on a rubber mat, you are insulating yourself. If you insulate yourself, the charge on your body will continue to build until there is enough voltage for you to discharge (i.e. receive a shock).

Standing on my bare concrete basement floor with bare feet stops it completely, but I don't recommend that. It is cold in your bare feet in the winter and if you lost the ground on the machine you might get a more serious shock because you are gounded to the floor and the machine wouldn't be grounded anymore.

The middle pin is the ground for the machine, correct? There shouldn't be a problem.

But yes, standing on the concrete will ground you, meaning the charge will pass through you to the ground. Your body will not build up charge like it would if you were insulated on a rubber mat or in shoes or something.

Back in high school, we did experiments with van de graff generators. Students stood on a stool, held onto the generator, and we watched their hair stand up. When they got down and stood on the ground, their hair went down. That is, the ground discharged them.

There are grounding bracelets available for working with computer chips that would work even better if attached to the machine on the other end. Then you, the machine, and ground would stay evenly charged.

Gary

That should work. Don't get the cordless wrist bands, though. Those are designed for computer equipment, and you aren't expected to build a large amount of charge working with computer stuff. If you try it for one of these, you'll probably build excess charge that the cordless strap won't be able to deal with, and you will get zapped again.

Anyway, I'm glad this thread was made. I am absolutely terrified of static electricity. I guess it's a phobia or something, but it's really embarrassing in public. Whenever I put my hand on a surface and I hear some clicking or snapping sound in the background, I jump

 

[gary jp4]

It is good to hear from someone that understands.

Definitely. If you stand on a rubber mat, you are insulating yourself. If you insulate yourself, the charge on your body will continue to build until there is enough voltage for you to discharge (i.e. receive a shock).



The middle pin is the ground for the machine, correct? There shouldn't be a problem.

.........................

True, but I have been shocked by equipment dozens of times that was supposed to be grounded. Luckly I wasn't in my bare feet on a concrete floor (or worse a wet concrete floor). It was never my equipment either.

In order to get shocked that ground wire/pin would have to be compromised and you would have to get power from the black wire, or motor wiring, to the chassis of the machine. This may be the golden BB, but I didn't want to give advice that got someone shocked. I don't think it is a good idea to use power equipment in your bare feet. I am more scared of house current then static. You don't use power tools in the bath tub, right?

Many years ago, in my youth, I had the pleasure of using a metal cased hand drill that my boss had just replaced the plug on. He put the green wire from the tool on the dark screw the black wire on the ground screw and the white wire where it was supposed to go on the plug. The green wire went directly to the metal case. The plug was the type with a metal band around the outside which was connected to the ground pin. When I plugged it in the wall the case was hot in my left hand and the plug was grounded in my right hand. I was locked in a death grip on the drill and plug and couldn't let go or move my arms. In a second or two I realized I could still move my legs and pushed off backwards. I fell on the floor and laid there for awhile. When I recovered I went looking for my boss and threw the damn drill at him as hard as I could.

So don't trust someone else's wiring, and do as I say, not as I do.

Gary

 

[Bigfattyt]

I have been electrocuted more than my fair share of times in life. Wet bare feet, wet concrete and plugging in a vacuum cleaner to an extension cord that was already plugged in at the other end. I have also been zapped twice by a broken light bulb with the prongs exposed (fell off a chair twice in a row while getting zapped, which was nice because by default it pulled my hand off the shocker).

Electric fences are a real good one also, done that several times.

With my little 1x30 grinder I can get quite the shock. Some times, it feels like mild electrocution, not just a simple shock. For a little while, I though the machine was shorting and shocking me, not just static. I agree that it is disconcerting while you have your hands near a fast belt to get jolted.

 

[Jason B.]

The first thing that you should do is try a figure out where the static charge is coming from. If you are only getting shocked when using specific belts I would say that its a belt issue any you should try grounding yourself. If you are getting shocked no matter the belt then your problem may be within the grinder. A loose/bad connection to the motor or inproper case ground could also be a reason for getting a static shock.

It could also be a ground issue with your house electrical.

 

[Roger999]

I've been shocked hundreds of times, I usually only get shocked when touching the tool rest, I have learned that I either don't touch the work rest at all or I touch the work rest non stop, if I'm grinding and accidentally touch the work rest, I usually get a nice shock, but I've never been zapped while always letting my hand touch the work rest. Where do you guys touch to get zapped?

 

[THG]

It is good to hear from someone that understands.

Well, I will soon be an electrical engineer

True, but I have been shocked by equipment dozens of times that was supposed to be grounded. Luckly I wasn't in my bare feet on a concrete floor (or worse a wet concrete floor). It was never my equipment either.

You're definitely right about that, though: if we're talking our typical 120V home AC, then it might not be a good idea to ground yourself. Just for reference: the idea is to avoid the current traveling through your heart. If you're grounded to your feet, the current is going to go from your hands out to your feet, meaning there is a chance that current will pass through the heart. Likewise, if you grab with both arms, current is definitely going to hit your heart. That's why it's recommended that when working with electrical equipment, use one hand, your right hand. That's pretty much the moral of the story

Anyway, for small static shocks, wouldn't it be better to be grounded?

 

[Tinbasher]

I get zapped a bit from my buff, never had one from the sander though.
Richard

 

[gary jp4]

Anyway, for small static shocks, wouldn't it be better to be grounded? Don't make it too complicated.

Yes, that is what I said, but it is safer to be grounded (connected) through the machine, not to another ground source.

First just connect yourself to the machine. Then go ahead and wear your tennis shoes, or stand on a rubber mat. Don't go barefoot like I did. Don't ground yourself to another ground source outside the machine.

Why:

You won't get shocked from static (at all) because you and the machine will equalized.

Using one hand while sharpening on a belt grinder is not practical.

If the ground is broken from the machine through the plug and the frame gets charged with 120v house current , you won't get shocked being connected to the machine because there is no path from it through you to ground (like there would be if you grounded yourself to some other source outside the machine like your bare feet on the floor or a ground bracelet to another ground source).

Gary

 

[Jason B.]

Grounding yourself would prevent the shock because you are dissipating the charge as it happens. The static charge could be happening for more than one reason though that's why finding its source is the most important step.

 

[YayILikePie]

While I haven't had this exact experience, I've had some troubles with static shock before. Every summer, when it gets really hot out, whenever I reach for my car door, I get one heck of a shock.

To prevent this, I went and picked up one of those electric shock bracelets. There are quite a few companies making these things, but I went a little fancy and got one that lights up when it's working. So far, it's worked like a charm. Even after wearing one, I still did occasionally get that shock, but it definitely does help. If you really want to stop it altogether, it's best to stay grounded. Copper wire connected to a faucet or something along those lines.

 

[gary jp4]

Here is the deal. With the case grounded, as it should be and everything working properly, it is normal to get a static build up with all common types of belts when running them on plastic wheels in low humidity.

When the humidity is low and you are using your Delta with a belt you have a 100% chance of getting a static build up on your body unless you are grounded the same as the machine.

You do need to determine if the shock is from static build up or 120v power source and differentiate between the two. If you are getting a shock from the machine from its power source, this is not a static build up. This is very different and should be obvious that it is not a static charge and is not what we are talking about here. Although, I was trying to prevent that from becoming an issue too by the way you deal with the static issue (risk management). A static charge makes a spark when it jumps to you.

Many experienced users are surprised that someone is getting a static build up because they never have. If you haven't' experienced it you have either been grounded or or not used the grinder in low humidity. Humidity in the air makes the air more conductive and dissipates static charges better. With a relative humidity of over 55-60% static electricity is not normally a problem. With a relative humidity somewhere below 50% static becomes a problem and a little lower it is a sure thing when using the Delta.

In most places low humidity comes with the colder seasons. In some places dry adiabatic winds (Foehn or Chinook winds), on the leeward side of a mountain range, bring low humidity with warm weather. You can also create very dry conditions indoors with air conditioning.

If it is a problem simply make a connection between yourself and the machine.

Gary

 

[drail]

Gary jp4 is correct on this. I worked in a shop with a large bead blast cabinet that would charge the operator to startling static levels. We finally attached a grounding clip to the operator and the cabinet and it stopped it. But as Gary stated you need to make certain that this is static buildup and not line voltage trying to find a ground through you. It is not at all uncommon to find improperly grounded equipment in many shops. Be careful. It's not just an annoyance, it can hurt you.

 

[gary jp4]

Yeah, I have found many appliances and tools that didn't have the ground wire (green wire from the plug) attached to the unit from the manufacture. It was just hanging there and not connected. You still have to have a leak (connection) form the hot wire to the case of the unit, its motor, or something, but that is common too.

I have an old Craftsman floor drill press that has a power leak so the whole unit is charged and has no provisions for grounding at the plug. I found out when I touched it once while it was running and I was in my bare feet. It may be an inductive issue from the motor or something. I checked the voltage from the case to ground and found 120v AC but, when I grounded it externally there was no spark and no short. I just run a 12# bare copper wire from a screw on the motor to the ground in the outlet box and I haven't had any problems with it in the last 25 years.

I have seen at least one shop and many houses where the ground wire from one circuit of outlets was not attached to the ground in the circuit breaker / distribution box and many outlet boxes where it wasn't attached internally.

As far as the blast cabinet and static goes, they create so much static with about any media used (sand, glass bead, plastic, nut shells, etc) that they are capable of developing a charge even when it is too humid for many other static problems to develop. When using a blast cabinet, and when grounding is not available, I sometimes rest my forehead on the metal above the viewing window to ground myself. Usually only after being shocked a few times and getting tired of it.

Gary