Static Dissipation Brush for Belt Grinder

Getting Rid of Those Nasty Belt Grinder Static Shocks

Anyone who has been happily grinding away on a knife and received a large and unexpected static shock can appreciate the unnerving discomfort of this arc. This shock, however, is more serious than the one you got when sliding out of the car seat and touching the door. It is a huge safety concern like someone sneaking up behind you and yelling BOO! A sudden reflex could send your blade into the belt or wheel where it could indiscriminately send it back to you very quickly. Here we are going to look at two options for managing static electricity on your belt grinder.

Why does this happen?

Static electricity builds up when two materials are rubbed together. This is known as triboelectric charging. Socks and carpet, hair and balloons and even belts, wheels and platens. 

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 grinder frame or other grounded equipment that snappy blue spark and familiar jolt gets you. 



That guy sure looks unhappy. Okay, so that's a really elementary way of describing it, but what can we do about it? 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 metal bristles to remove the charge from the belt before it builds up on you. 

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

From the comments I have read in forums about static electric shocks on belt grinders it appears that many people do not understand what is happening. Phrases like "make sure your grinder is grounded" and "add a green wire back to your electrical panel" are not going to help. Yes, it is required by code that your machine be bonded to earth via the green wire in the power cord, this bond doesn't take the charge buildup on your body. It just makes it extra sparky when you do finally touch the frame!


The Brush

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


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 it meets the handle part. It will be about 1.5 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. The screw must touch the bristles. Attach the bracket to the head and we're done.

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 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 the BG-272 I have included a welded on 1/4" bolt specifically for installing the brush.


I added a short handle to the top of the bracket and secured the bracket with a nylon locking nut. This allows me to rotate the brush around the mounting bolt. The reason for this is when I switch the large contact wheel the belt path changes slightly and the brush was dragging on the back of the belt.

Although I live is a dry climate area I have not received any static electric shocks from my grinder. In the winter months, it is not uncommon to have relative humidity around 20% and we get shocks from taking off a jacket to sliding out of the truck seat.

Do Nots

If attaching wires and chains to your body is your thing, do it in the bedroom! A belt grinder is not a place for anything loose to get caught in rotating parts. Even an anti-static wristband like those used in the electronics industries would be bad slapping you in the face as it's stuck on the side of your contact wheel. 

Do not take your shoes off. Although this will help dissipate the charge from your body through to the floor, it's a bad idea to be blowing hot steel sparks on your toes.

I hope this serves you well and reduces those nasty static sparks. Of course the hot steel ones are okay.

Safe grinding!

Dan

11 comments:

LJ240 said...

Dan,

You never seem to amaze me. This post really clearified what I needed to know.

Thanks.

D. Comeau said...

I'll keep trying!

Unknown said...

Very informative, I cured my static problems by attaching a computer nerds earthing cable and wrist strap. I work with acrylic and wood, no problems now.
Rob

Unknown said...

I am following a discussion on facebook on this subject. Your explanation makes sense to me. As well as the undesirable ESD wrist straps there are also ESD conductive bench and floor mats that are connected to ground. These mats have a high resistivity and although they conduct the static charge away, they do not pose a danger if you inadvertently touch a live wire. I haven't tried this with grinders/buffers but suggest that one of these floor mats might solve a lot of anti static problems. You can also buy work boots/shoes with antistatic conductive, (high resistivity), soles for use with these mats to make the discharge circuit even better. Congratulations on your website, I have looked at hundreds of knifemaking sites and as far as I am concerned you are No.1.

D. Comeau said...

Thanks!

I work in electrical/electronics manufacturing and we used a number of methods to reduce the risk of damage to electronics includings straps, mats and sprays.

In industrial settings we use brushes and tinsel to safely draw static charge away from non-conductive (usually EPDM or polyurethane) rollers.

For a belt grinder, the logical choice is to drain the charge away before the operator gets some.

Safe grinding!

Dan

Unknown said...

I am almost done with my build and for the brush I am using a tube brush for anti-static. Tube brushes usually have a twisted wire shank with a loop on the end and about 4 inches of brush. I folded the brush in half, bent the shank 90 deg and closed the loop on the end a little to fit the bolt. If it takes a hit, it can be bent back.

D. Comeau said...

Hey, that's a great idea.

Happy grinding!

Dan

Unknown said...

If one or all of the wheels are metal with an electrical path to the grounded frame, e.g via bearings and non painted surfaces (bolts biting through paint etc) would static build up on the belt still be a problem? I can see how static would build up if the wheels were non-metal, however was wondering if a leakage path was sorted out as part of the metal drive wheel for example in the initial design phase a static leakage brush won't need to be added?

Thank you so much for sharing your knowledge through this website, I've been reading a lot researching my linisher build and really appreciate the effort you have go to sharing this information.

Did you ever write anything on using treadmill motors as alluded to in your motor information section or decide not to go there due to their unsuitability with the open frame? I'm considering using one just to keep the size of everything small for my space/use since the 2x72" belts aren't as available here as the 2x48" belts. I liked the idea of the filter on the end of the motor as shown in your gallery.

Thanks again. Steve.

D. Comeau said...

Hi Steve,

Good question. I have grinders with both aluminum and glass filled nylon wheels and they each were setting up static charges equally well. I suspect that the grease in the bearings doesn't conduct well from the wheel (outer race) to the axle bolt (inner race). The worst is during dry weather and especially working the slack belt i.e. not touching the frame, work rest etc. I did read some articles regarding the application of conductive grease to the bearings, however this didn't appear to the very effective at higher speeds where centrifugal force slings the grease to the outer race.

A while back I got a DC treadmill motor running on my lathe, which is well protected and works ok. Although many grinder makers are using them successfully, I would not recommend a treadmill motor for a metal grinding machine. Attaching a drive wheel is a bit hit or miss. Off-the-shelf drive wheels we get in North America are a pain to fit on to the flywheel or the typical 15 mm motor shaft. Also, as you mentioned, the open frame and the strong permanent magnets inside the motor are really good at attracting steel. This could be overcome with filters and external magnets. Then there's the dozen or so fried controllers people have asked me to help them with. Too many worms in that can.

If you do go with a treadmill motor, I'd suggest that you keep the flywheel on the external fan if it has one. For most treadmill motors the airflow to cool the insides is produced by vanes in the flywheel. The flywheel also offers energy storage to help you get though load changes when grinding.

Good luck with your build. Send me a pic when you get it up and running.

Cheers!

Dan

Ellis said...

Hi Dan, I've been making knives for about 20yrs, and stumbled across your site while looking for a hollow grind calculator. But I must say your site is a great wealth of knowledge for all bladesmiths. So anyway after all this time I am no longer shocking the hell out of myself while grinding. Thanks for the tip!

D. Comeau said...

Hi Ellis,

I am glad to hear you have found some useful info on this blog. Happy grinding!

Dan