Turning Archive

Subject:
Re: HAZARD with CBN wheels

John K Jordan
I think the problem at my grinder was actually the use of the magnet! The collected dust formed a big fuzz ball with longer tendrils of incredibly fine steel dust from the 600 grit wheel, most spread out so with lots of air. This fuzz ball was in the perfect position to catch a spark. On a coarser wheel I had no magnet so some steel dust collected on the table under the wheel - it was subject to lots of sparks but probably didn't ignite since it wasn't spread out in the air.

>>>I was sharpening yesterday for a demo, and when done and loading the grinder, I noticed round dots on the wall where the sheet rock screws were. The particles are magnetized some how with the grinding process. ...

It could be that the sheet rock screws themselves are magnetized instead of the dust. Perhaps the installer used a magnetized bit. You could test this by placing some bits of demagnetized mild steel (nuts, washers?) under a sheet of white paper near the grinder and see those spots collected more dust than the rest of the paper.

Also, some people have called me loony when I mentioned but it's a fact that steel can become magnetized just by sitting for a while in a magnetic field - even the earth's magnetic field is enough. There is a lot about this on the internet, some of it experiments for kids.

When something of the right kind of steel simply remains stationary it will slowly become magnetized, accelerated if tapped or vibrated. I first noticed by checking a refrigerator with a compass - it was one pole at the bottom and the other at the top. Cans on the pantry shelf were the same.

The worst in the shop is lathe tools. They will be become magnetized in use, I think because they are often held in about the same position and subjected to vibration from the turning. This gets annoying when sharpening with a dry CBN wheel on the Tormek where the wheel is rotating away from the tool edge. The tool will have a black trail of fine steel dust attached to the edge which obscures it and makes it harder to sharpen. I keep an old hand-held bulk tape eraser near near the grinders to demagnetize tools as needed. There is also a trick to demagnetize with a permanent magnet if anyone is interested.

I've been monitoring the fine steel dust floating around my shop with magnets placed in various places. It's amazing how far it will travel. Probably not beneficial to the lungs...

JKJ

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