Variable Speed Control Hacks ?

C

Charlie P

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Jun 14, 2018
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I'm starting on the ground floor and I bought a Grizzly 2x72 belt grinder. (plez no $hit storm of "you bought junk" comments ;)) What I'd like to know ... is there any reason I can't use a better quality router speed controller to turn this single speed machine into a variable speed machine?

Thanks in advance ! :D
 
I believe I recall seeing where an individual put a pulley on the buffer side and drove it with a vfd package (IOW, a completely separate 3 phase motor) but other than that, there’s not much you can do with the current out of the box setup.
 
On that type of motor, small degree of speed control is possible but seriously not worth messing with. Its torque will drop off signifigantly as its slowed.
Depending on its motor type, can cause its start winding to energize then burn up.
 
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You would have to move all the parts over to a 3 phase motor and set up a VFD for that. But i'm not an electrician, there might be other ways that I don't know of.
 
Stacy E. Apelt - Bladesmith said:
Short answer - No it won't work.
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Why not? That looks like a single phase motor and there likely aren't any additional electronics internally. It may not be wise to do so as running to low would probably have the motor stopping and too high will damage it but it should work if one's inclined to do so.
 
A lot of single phase motors are capacitor start and the capacitor disengages once the motor is up to speed. If the motor slows the caps kick back in. If the motor runs for to long with the caps connected then the motor will pull to many amps and burn out.
 
Even if it is a standard single phase motor without starting capacitors, the "speed controls" used on routers won't run it for VS.

Well, that isn't exactly true - they might run it for a while before it burned up.

Fancy Words deleted

Now if you are dead set on proving us wrong, and buying a new Grizzly grinder isn't a big deal - go ahead and do it. Let us know how well it works out for you.
 
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Stacy E. Apelt - Bladesmith said:
Even if it is a standard single phase motor without starting capacitors, the "speed controls" used on routers won't run it for VS.

Well, that isn't exactly true - they might run it for a while before it burned up.

Without getting into technical detail on sine waves, frequency response, heat distribution and generation, torque drop, and how the motors are wound, suffice to say they most single phase motors on shop equipment can not be run on a speed control. As Penn Jillette says, "I think I have given you enough of a hint with those words to let you know..."

Now if you are dead set on proving us wrong, and buying a new Grizzly grinder isn't a big deal - go ahead and do it. Let us know how well it works out for you.
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Feel free to hit me with the technicalities, I'm currently in the process of becoming an technician for electrical engineering, I'll get it (though I didn't have to do stuff with motors since my apprenticeship).
A motor with starting caps will die, absolutely yes, but I don't think a grinder has starting caps.
Other than that if you slow down too far you'll have a bigger voltage on the cap which isn't great but it won't die instantly, same thing is if you run it too fast, your coils will probably die. But that's what I had in my original comment, your kinda limited in your range.
 
Because the torque loss in a single phase induction motor is so severe. You can vary the speed. That part works. But when you do it becomes next to unusable. That loss in torque is the symptomatic of the oscillating magnetic field and the loss of inertia in the stator when it's speed is reduced. A 3ph motor has a revolving magnetic field and therefore can produce full torque from zero rpm.

Torque loss in the face of work results in higher power draw. Using a variac to vary voltage means increasing current draw at lower voltage. This is what will heat the motor and "burn out" the windings.

They work on universal motors with brushes and comutators because of how they're wound and in effect the commutator creating a large number of poles that don't exist in an induction motor.

If it worked we would all do it. I've even gone so far as attempting to run a 1ph motor off a VFD. Same problem.

Why don't you think a Grizzly single phase grinder has starting caps? It has both start and run caps.
 
I somehow convinced Purdue University to put my name on the bottom of a 4 year sheepskin for Electrical and Computer Engineering Technology, and if they ever shared how to efficiently vary the speed of a single phase induction motor, I must have slept through it.

Kuraki basically covered it. Yes, speed change is certainly possible, but it's gonna be at a trade off that usually ends up cooking a single phase motor. There are single phase speed controllers that use PWM to get the job done a little more "safely", but you're still going to lose most of your torque, and for what most single phase VFDs cost, you could buy at least a couple of 3 phase setups.

If SCR/Router speed controls were a viable solution, Grizzly would already be incorporating them into their grinders, and none of us would be spending hundreds of dollars on 3 phase VFD rigs. I imagine that if there were ANY low cost setups that still offered constant torque at lower speeds, Grizzly would have gone this route as well.

OP is free to try anything he thinks will work. On the bright side, when the motor burns up, you can do a mod like this to make it variable speed:
1h4dja
 
Nothing wrong at all starting off with the Grizzly. Anyone who gives you a mouthful is likely a fool that uses his $4000 grinder to grind the JUNK steel he picked up off the road to forge!

Variable speed is nice but certainly not necessary. I used a single speed Dayton converted to 2x72 for years, until I finally built my own. If you absolutely must have a slower speed, you can use a smaller drive pulley, or grab one of those 2speed drive wheels.
 
One Armed said:
Nothing wrong at all starting off with the Grizzly. Anyone who gives you a mouthful is likely a fool that uses his $4000 grinder to grind the JUNK steel he picked up off the road to forge!

Variable speed is nice but certainly not necessary. I used a single speed Dayton converted to 2x72 for years, until I finally built my own. If you absolutely must have a slower speed, you can use a smaller drive pulley, or grab one of those 2speed drive wheels.
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There’s no drive pulley on the grizzly, as the Contact wheel/drive wheel are one and the same. A smaller drive/contact wheel COULD work, to an extent I suppose. The 2 speed wheel may actually be an option as well, since the shaft on the grizzly is 5/8” if I’m not mistaken. You sacrifice having a contact wheel, but if you mainly use the flat platen, it may be worth looking into.
 
I think the statement "it has both start and running caps" is not really accurate. Typically there is a centrifugal switch that connects the auxillary winding to the cap when the speed is below a threshold. That is why a stalled motor can restart itself when unloaded. So there normally isnt but one cap. I dont know how they do things in taiwan or wherever though.
 
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