How To Motorize Your Mill's Z Axis

[henryarnold]

(06-16-2012, 06:29 PM)stevec Wrote:

(06-16-2012, 12:03 PM)henryarnold Wrote: I decided not to supply an example schematic because of safety issues with the way it might be assembled. The schematic I was going to publish used 120 VAC as an input and could pose a shock hazard if not assembled correctly. This issue is why all of our 2 prong power tools are double insulated.

Gimme a break!

Steve,
I was trying to help others by showing one possible way to motorize a mill's Z axis. Since you seem to have a problem with me not posting the schematic, I will go ahead and post the schematic with an warning about why it could be dangerous. Maybe some of the members would like to make suggestions for improvement or a better motor controller all together.

   
The reason that this DC power supply can be dangerous is that the hot lead from your AC wall outlet comes directly into the circuit and through one of 2 diodes to the motor. If the motor internally shorts and is not properly grounded, the motor frame or even the mill could be electrified. I've seen this happen with a refrigerator where touching the handle gives you a shock. The ways to assure this doesn't happen are to make absolutely sure that the motor chassis is tied to ground, use an isolating transformer or motor controller, or insulate anything that touches the motor so that a short can't electrify the chassis (like hand power tools). My concern is that someone using this circuit while failing to ground the motor, could get hurt if the motor was faulty. The other problem is that even if you do everything correctly, your outlet's ground may be faulty leaving a potential hazard. The best solution is to buy either a motor controller or isolated DC supply.

One of the things that has been refreshing about this forum is the patience members show towards each other. We are all trying to learn and have fun with metalworking. I hope the forum keeps this atmosphere.