Magnetic Chuck Control Circuit Wanted

MozamPete said:
BOB, THAT SHOULD WORK FINE ;)
I'm thinking of just switching between different control modes/driver circuits for a single SCR/PWM voltage controller:
1. Fixed 110Vdc output for normal/full power
2. The normal pot for variable power (not sure when this is normally used, I'm guessing for part hold during setup of the workpiece or for reduced heating if the workpiece geometry is such the enough hold can be obtained at reduced voltage)
3. Off
4. De-mag ramping/alternating polarity
Click to expand...
I also have a drum switch I could use to manually reverse the DC polarity, back and forth, while I ramp the input voltage down manually with the variac. That was my first idea. Apparently there is some disagreement on whether AC or DC is better (or perhaps more expedient) for demag. I wish I understood demag better...
 
MozamPete said:
BOB, THAT SHOULD WORK FINE ;)
I'm thinking of just switching between different control modes/driver circuits for a single SCR/PWM voltage controller:
1. Fixed 110Vdc output for normal/full power
2. The normal pot for variable power (not sure when this is normally used, I'm guessing for part hold during setup of the workpiece or for reduced heating if the workpiece geometry is such the enough hold can be obtained at reduced voltage)
3. Off
4. De-mag ramping/alternating polarity
Click to expand...
Peter, I must admit to not understanding well the circuitry for SCR and PWM controllers, so I would need a complete circuit diagram and an understanding of it before I would go in that direction. Another thing I am trying to achieve here is a variable magnetism force to better accommodate both heavy and solid as well as thin and flexible parts for both machining and hand scraping, and perhaps other currently unanticipated work holding chores as well.

Edit: This is intended to use a chuck and some other stuff I have on hand to achieve something that works for occasional odd jobs. This will not be 40 hour a week tooling...
 
The biggest advantage electromagnetic chucks have over fixed magnet chucks is the ability to control the strength of the magnetic force generated. There are also disadvantages, not the least of which is the possibility of throwing a part off a machine due to losing electric current flow to the chuck. In my mind, any controller should keep both of those tenets firmly in mind.
 
This is a great discussion and learning opportunity for me, and hopefully for others as well... Thanks, all, it will be interesting to see what ideas we can come up with.
 
Bob Korves said:
There are also disadvantages, not the least of which is the possibility of throwing a part off a machine due to losing electric current flow to the chuck.
Click to expand...

I hadn't thought about that :eek: Good point. I'll be designing mine with a UPS in the circuit.
 
I also have a mag chuck with no power supply, I was given 10 years ago, I have a monster power supply that I can use but building a dedicated one would be great. Looking forward to a simple diagram to build that I can understand with no circuit board. Thanks.
 
I have two factory built controllers that came with my surface grinder. One is a very old 460v unit with two thyratron vacuum tubes, the other is not quite so old and has a multi plate selenium rectifier and a drum switch. I think those are pretty worthless for my needs. I am not above scavenging anything useful from them, but about all I see that might be useful to me is the drum switch.
 
Mine is a LW CHUCK Co TOLEDO, OHIO. it is a 6X18 and at least 100 lbs, it is marked 110VDC at 1.0 amps. I researched the internet and found nothing but found other controller in the 800-1000 dollar range, wonder why I have never needed it that bad. I would like to make my input 120VAC since it is available in the garage everywhere, no 460 here or any 3 phase.
 
Rick just look for an isolation transformer at about 300 watts and a bridge rectifier rated at about 400 volts at 10 amps. A couple small high voltage capacitors to protect the bridge from spikes. I can post a diagram if you need one.
Shouldn't cost more than a couple hundred, maybe less. The chuck should have a good solid ground.
If you need to adjust the magnetic force you would need to add a variac to the circuit (more cost).
Mark S.
ps a GFI would be a good idea too
 
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