This may be impossible to do but my husband has a grinder and he's worried about the direction it's turning and wants to reverse the polarity so it runs in the other direction. As I know my son got injured because the grinding wheel runs against the rest (clockwise) and got his finger caught between the wheel and the guard... I'm inclined to agree with him...

I've looked for this answer but find answers to DC current but not particularly AC. This isn't a tiny motor.

First... is there any reason why the grinder must run in this direction and can he reverse the polarity to reverse it without a destroying the grinder?

I'm not into electronics but I know the bare bone basics. Make sense to me and I can understand you.

Becca

Reversing the grinder will cause you more problems. Three in particular: 1) The piece will jerk upwards and you will be constantly fighting it 2) Removed metal will fly into your eye and face even with safety glasses and 3) if the stone should ever shatter )you figure it out).

As for some tips:

Keep the rest close to the wheel. Say 1/8 of an inch.

Do not grind on the side of the wheel.

Get a grinding wheel dresser and dress the grinding wheel periodically.
Grinding dresser - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Grinding_dresser)

The grinder likely cannot be reversed for the above reasons.

I believe what she is saying is that the motor is already running the wrong way, and she wants to change it, to the correct direction.

What type of motor is it, 120 vt, 220 vt

...my husband has a grinder ...and wants to reverse the polarity...

Typically an ac motor can be reversed by reversing two of the motor leads. There is usually a wiring diagram inside the electrical box on the motor with instructions. If it is a grinder targeted at home consumers instead of an industrial model, all bets are off. They may have specialized motors. An electrician or motor repair shop could probably reverse it for you though if that is the case.


...my son got injured... I'm inclined to agree with him...

I'm not so inclined. The down turning wheel forces the work against the rest and allows the operator to only have to be responsible for control and not resisting the wheel's desire to throw the work. Your injury sounds like improper technique.

The consequences of the wheel rotating up are potentially more dire than a pinched finger. In addition to sparks being thrown in the operator's eyes, there is a risk that the work could grab depending upon how it was fed into the wheel and be thrown impaling the operator, most likely in the face. Up grinding can be preferable for specific tasks, like honing, but which is also done at slow speed and low to moderate pressure.

See OSHA Small Business Handbook (http://www.osha.gov/Publications/smallbusiness/small-business.pdf) for abrasive wheel equipment grinder adjustment recommendations.

Be safe.

No it is not running in the wrong direction... it's running the way it was set from the factory. I agree with KISS's explanation to why it's running clockwise rather than counterclockwise. My son got his finger caught but in retropect the alternative could be devastating. Thank you and hopefully my husband will give up his misson to change the direction.

Becca

Motor is running the correct way and should not be changed.

Learning technique and safe operation is very important.

Let me ask a couple of questions:

What material was being ground at the time of the injury? It better not be aluminum. Carbide requires a special wheel.

Was there water nearby to dunk the metal part to keep it cool?