Mark's schematic looks good; just remember to remove the line with the X!
The bridge rectifier converts the incoming AC to pulsed DC. The capacitor and the inductance of the chuck will combine to smooth out the current in the chuck. The resistor next to the capacitor is there to bleed off the charge in the capacitor; you need it!
In this schematic that series resistor is being used to apply AC current to the chuck. The tricky spot is figuring out how much AC current you need to reliably demagnetize it.
I think you are going to find that the switch burns up very quickly. The energy stored in the chuck's magnetic field is going to end up in a big spark inside the switch!
I suggest you look at the circuit for the Magnabend instead.
http://aaybee.com.au/Magnabend/Handyman_Pages/Electrical Circuit.html
You can leave off the bending beam microswitch, start button, C3, C2,D2, thermal switch, and relay coil. Substitute a double pole double throw switch (NO CENTER POSITION) for the relay poles. Your AC power will go directly to "relay pole 1"; note that this is the common to normally open side of the switch. The other side of the switch is wired up in place of "relay pole 2". Again, note the NO vs NC positions!
What happens is closing the switch hooks power to the bridge AND feeds from the bridge to the magnetic chuck. The chuck will power up and hold your parts. When you are done, flip the switch the other way/off. This turns off power and connects the chuck to the de-gauss capacitor. NOTE, during the transition when all the switch poles are not connected to anything, the chuck current is allowed to continue flowing either through the bridge or C1/D1. This is an important safety and durability feature! When the contacts finish switching, the energy stored in the chuck is moved into charging up C1. Once the coil current has reached zero, it reverses as the energy in C1 goes back into the chuck. There's a LOT of losses in this circuit, so the back swing generates a lot smaller magnetic field.
BTW, you can build up more of his circuit if you want to; the pre-clamping phase that uses C2 could be useful for setup.
Here's where I talk about my magnabend build and the capacitor required. Actual oscilloscope pictures too ;-) I used a bigger capacitor than Alan; about 6,000 micro Farads. Too small and you over-voltage the cap and risk it exploding.
I'm very pleased! Sent from my SM-G892A using Tapatalk
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