View Full Version : Is it practical to make your own mag chuck control?

Ian B
08-17-2001, 10:26 PM

Could it be that most of the magnetic chucks on HSM-sized surface grinders don't need power supplies - they have permanent magnets, and a lever that aligns or misaligns the poles to switch them on & off?

There certainly are electric ones around - but 6" x 18" is a pretty common size for the permanent magnet type - wouldn't one of these do for what you need?


03-03-2006, 09:47 AM
Lets assume I find one on ebay with a guarantee to work but does not have the control. Would it be easy for a novice to make one? I don’t even know what kind of current they use. I would guess DC since its supposed to reverse(?) to de-magnetise. I would not need less than 100% force. I’m looking for a 6x18” for a surface grinder.

Why is it that I see tons of magnetic chucks on ebay but they never include the control? I have to wonder if they are selling it that way because it was shot and replaced with a new one.

What happens to a mag chuck if it is ground too thin?

Super Dave
Rapid CNC

J. R. Williams
03-03-2006, 10:20 AM
A DC magnetic chuck requires a power supply that is set to reverse the polarity in a series of reduced power steps when the power is turned off to demagnetize the work. No problem to build a simple DC supply to hold the work but the reversing and power reduction control is not easy.


herman williams
03-03-2006, 07:48 PM
I made a couple. I used a variable transformer for supply voltage. Full wave bridge for the D.C. supply. Regular barrell switch to apply voltage with reverse to apply ac to demag whatever you are holding. The variable voltage is necessary for thin material since full force has a tendency to warp thin material. All the units I have worked on require about a hundred volts at three or four amps for full power.

03-03-2006, 09:58 PM
I have a 90vdc control at work,two actually,one is in use the other is a spare.

All it has is a drum switch and a selinium diode rectifier.The drum switch selects between taps on the rectifier to get the different voltages,at least that's how I think it works.

When you turn the control to "off"a five second timer pulses the mag with AC to demagnitise the part.

Bill Cook
03-03-2006, 10:25 PM
I couldn't wait to use the chuck that came with my surface grinder. Well actually didn't NEED to use it.
Reworked a diode set from an old automotive altenator. It's rated for a much higher amperage and it produced the 115vdc under load specified on the chuch tag.
Since the heatsinks are hot (electrically), I dropped it in a small corrugated box with the cords coming out from under the lid. (It doesn't reach luke warm).

Does the job, but the lesson I probably should absorb THIS TIME is that it's likely to be permanent.


03-06-2006, 11:18 AM

03-07-2006, 09:01 AM
I was looking specifically for an electric one because I got burned on a permanant magnet type. As soon as I used coolant on it rusted tight. Not that it mattered anyway since it would not demagnetize anyway before. My quess is that it siezed up with a previous owner who tore it apart. I believe that is a no-no with permanant magnets tools.

I'm not an electrical genious to set up the electric control (thanks for your replies anyway, guys). I just bought a cheap new permanant mag. Hopefully it is sealed better to keep the coolant out.

Super Dave
Rapid CNC