A request for information on your mill or lathe

[nova_robotics]

Don't know the exact term, but there is an issue where stray current erodes contact areas of bearing components and races. IIRC, VFD rated motors have additional frame grounding to bypass the bearings.

Do they rely on the spindles discharging static through the workpiece? So for example the bearings in a mill used to machine aluminum will last longer than a similar mill used to machine UHMW?

My router table produces an ungodly amount of static when running. It's basically a Van de Graaff generator. The spindle is 3 phase VFD driven. I'm now questioning whether I should try grounding it or not. I really want to take that spindle apart. Perhaps it could use some conductive grease and a ground strap.

[rgsparber]

Do they rely on the spindles discharging static through the workpiece? So for example the bearings in a mill used to machine aluminum will last longer than a similar mill used to machine UHMW?

My router table produces an ungodly amount of static when running. It's basically a Van de Graaff generator. The spindle is 3 phase VFD driven. I'm now questioning whether I should try grounding it or not. I really want to take that spindle apart. Perhaps it could use some conductive grease and a ground strap.

If you are running CNC, the static must not be getting into it or you would crash. I'm sure your machine body is grounded so you should not get shocks from static discharge by touching it.

Static discharge current could be flowing through the motor's shaft, bearings, and into ground. My guess is that if there are sparks, they occur millions of times a minute. If the motor hasn't failed yet, it is probably fine.

Rick

[nova_robotics]

If you are running CNC, the static must not be getting into it or you would crash. I'm sure your machine body is grounded so you should not get shocks from static discharge by touching it.

Static discharge current could be flowing through the motor's shaft, bearings, and into ground. My guess is that if there are sparks, they occur millions of times a minute. If the motor hasn't failed yet, it is probably fine.

Rick

The spindle is isolated on that machine. The table is grounded. So if you lean over and touch the spindle when running, your body general makes contact with the table grounding you out and you get a big shock. If machining plastic you can get a shock probably every 10 seconds off of the spindle motor. It's so bad the chips jump off the table because of the charge.

[Frank S]

Now that you mention it my 2x48 belt sander gives me a small shock sometimes. I try to avoid touching the frame while grinding but, the shock is sometimes even felt through the work piece when I make and break contact with the rest. I thought it could be a bad ground but after checking I couldn't find any problems. Gloves are such a pain to even remember where a pair are, insulated plier does the trick for small items. There is no way I would have ever correlated a belt sander with the Van de' Graff, but now at least a possible direction for a solution has been made available. Thanks to all for the tip.

[nova_robotics]

Now that you mention it my 2x48 belt sander gives me a small shock sometimes. I try to avoid touching the frame while grinding but, the shock is sometimes even felt through the work piece when I make and break contact with the rest. I thought it could be a bad ground but after checking I couldn't find any problems. Gloves are such a pain to even remember where a pair are, insulated plier does the trick for small items. There is no way I would have ever correlated a belt sander with the Van de' Graff, but now at least a possible direction for a solution has been made available. Thanks to all for the tip.

No probs. Just make a single metal pulley and put it at the top. That way it grounds out the belt before it has a chance to shoot little zaps into your fingers. Maybe replace the slider/platen thing that holds the sandpaper against your workpiece with a metal one? There are probably a few different ways to prevent charge from building up on the belt.

But really when you think about it, we're intentionally CAUSING the thing we've spent the whole thread trying to avoid. You are now grounding out your belt through a bearing. I've been using the crap out of mine for years like this and haven't had to replace a bearing yet. I'm sure it's accelerating bearing wear, but those bearings are easily changed and only a few dollars. A mill spindle bearing is a different situation.

[Frank S]

No probs. Just make a single metal pulley and put it at the top. That way it grounds out the belt before it has a chance to shoot little zaps into your fingers. Maybe replace the slider/platen thing that holds the sandpaper against your workpiece with a metal one? There are probably a few different ways to prevent charge from building up on the belt.

But really when you think about it, we're intentionally CAUSING the thing we've spent the whole thread trying to avoid. You are now grounding out your belt through a bearing. I've been using the crap out of mine for years like this and haven't had to replace a bearing yet. I'm sure it's accelerating bearing wear, but those bearings are easily changed and only a few dollars. A mill spindle bearing is a different situation.

I may have to try other solutions the platen is metal and the top roller is aluminum. Since it mostly happens when the back of my hand or along my fore arm happens to touch the grinder / belt sander housing but only under certain conditions like on the rare higher humidity days something that goes against my belief of it having to do with static electricity alone. I am more inclined to believe what I am experiencing is possibly a dust trail either in the motor itself or in the wiring to the switch. I am thinking the humidity and if it is dust is possibly acting like an impedance capacitor in some way which discharges to my touch. Does any of that make sense?