# Variable Speed Motor For Quorn T&g Grinder



## old toolmaker (Nov 8, 2016)

I have an almost complete Quorn Tool and Cutter grinder in need of a suitable motor.  I have a Dayton 1/8 hp fan motor on it now and it is under powered.  I t should have a minimum of 1/6 hp and 3000 - 4000 rpm.  I would like to use a variable speed DC motor to eliminate pulley changes when using wheels smaller than 4".  The problem is I want a small physical size motor of less than 5 pounds if possible and face mount.  I also don't want to spend a fortune.  Any suggestions?

Dick


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## old toolmaker (Nov 8, 2016)

I have found on E Bay a new 1/4 hp 12 volt brush type DC permanent magnet motor about 2-1/2" diameter x 4" long that I think will work with a DC controller that I already own. My controller is for this type of motor but I may need to get a different resistor as the controller is currently sized for a 90 volt motor.  The motor is small in physical size for the hp produced, which is what I wanted.  It is also face mount.

Dick


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## British Steel (Nov 13, 2016)

Hi Dick,

If the controller you have's one of the KB KBIC120 or clones, the resistor sets max average current, NOT voltage, it'll still try to provide 90v pulses that average to the current it's delivering to the motor. Magic smoke may escape. A pic of the controller would help, someone might be able to identify it and that could point you to the right motor.

If you run a 12v DC motor you're likely to need more than just a controller board, some way of getting down to near 12v is probable, an old start & charge battery charger transformer maybe (thrift shop?)? Add a diode bridge to get from AC to DC and you're almost there - then there are DC motor controller boards on EvilBay, many come cased and just need DC in and motor connections.

For Safety, a fuse in the AC supply is a bare minimum, I've opted to fit magnetic circuit breakers (MCB) where I can (easier than trying to find somewhere that sells *the right* fuse on Sunday evening!) - I also put a MCB in the transformer output wiring N.B. they don't work well on DC unless you find a specialist and pay the price, put one (e.g. 16 or 20 amp for 1/4 HP on a 12v supply) in the low voltage *AC* line coming from the transformer.

Hope that helps. rather than confuses!

Dave H. (the other one)


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## old toolmaker (Nov 13, 2016)

British Steel said:


> Hi Dick,
> 
> If the controller you have's one of the KB KBIC120 or clones, the resistor sets max average current, NOT voltage, it'll still try to provide 90v pulses that average to the current it's delivering to the motor. Magic smoke may escape. A pic of the controller would help, someone might be able to identify it and that could point you to the right motor.
> 
> ...



Dave,

I have since gotten quite an education on DC motors and controllers.  I returned the 12 volt motor I had purchased.  My controller is a KBMD 240 D Multi-Drive.  You are very correct in noting that I must use a 90 volt motor with this controller.  The controller itself was given to me by my brother and is in beautiful condition cosmetically.  I like the features it has such as dual voltage input switch (115/230 v), trim pots for several functions (max speed, ramp up and down, etc.).    One question I do have is:  Does this controller I have supply constant full power even at low rpm or is does it use PWM. (I am not sure if I am using correct terminology here)

I also have learned about VFDs and controlling 3 phase motors on single phase input.

Dick


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## rdhem2 (Nov 13, 2016)

Try looking into Grainger or Johnson Controls for your DC Motor.  They have a pretty good selection in sizes and voltage ranges.  When you are in such low voltages employ glass fuses as they are not so expensive to keep an extra five pack laying around in the spare parts drawer.  Like the othe fellow said, fuses do not let out near as much smoke as other electrical componets.  Now go sharpen those tools up!

Silly question, have you ask Quarn about a replacement motor?


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## British Steel (Nov 13, 2016)

Hi Dick, looking at the datasheet online, it's very similar to the KBIC (bare board) controller, so it is PWM - this is the most efficient way to vary the speed of a DC motor (in my opinion!), and gives constant-ish torque through the speed range - simply put, it uses the AC by rectifying it to "lumpy" DC then gating each "lump" into the motor to get a voltage that averages to what the motor wants for the particular speed (pulses of 90v, so letting half the pulse width though makes it average about 45v etc.).  So, the 60 Hz power is rectified and gives 120 lumps per second, the speed's reduced by letting progressively less of each lump through to develop torque and power in the motor - hope that makes sense?

Russ, the Quorn's a home-brew tool & cutter grinder, first published as plans in Model Engineer in the UK some decades ago - no actual manufacturer (other than raw castings!), no two are the same and the motor etc. is left to the builder to choose and adapt!


P.S. - on edit, the control potentiometer on these controllers is at half line voltage, so be careful it can bite if not safely insulated (particularly on 240v like here in Europe) and if the control's leads are shorted to ground it will take the board out...

Dave H. (the other one)


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## old toolmaker (Nov 13, 2016)

British Steel said:


> Hi Dick, looking at the datasheet online, it's very similar to the KBIC (bare board) controller, so it is PWM - this is the most efficient way to vary the speed of a DC motor (in my opinion!), and gives constant-ish torque through the speed range - simply put, it uses the AC by rectifying it to "lumpy" DC then gating each "lump" into the motor to get a voltage that averages to what the motor wants for the particular speed (pulses of 90v, so letting half the pulse width though makes it average about 45v etc.).  So, the 60 Hz power is rectified and gives 120 lumps per second, the speed's reduced by letting progressively less of each lump through to develop torque and power in the motor - hope that makes sense?
> 
> Russ, the Quorn's a home-brew tool & cutter grinder, first published as plans in Model Engineer in the UK some decades ago - no actual manufacturer (other than raw castings!), no two are the same and the motor etc. is left to the builder to choose and adapt!
> 
> ...



Hi Dave,

So, if the KB unit I have is PWM, then I could actually use the reasonably priced plain chassis units sold on E Bay and elsewhere?  The only thing I would actually need would be a transformer to reduce 115 volts AC here in the US to 12 volt DC and supply an enclosure of some sort.  That is if I understand it correctly.  I am certainly learning a lot here and I really appreciate the help.  
At present, I have a 115 volt AC 1/8 hp. motor running at 3000 rpm driving a 4" flaring cup diamond wheel through a couple of pulleys giving me about 3200 rpm at the wheel.  A little slow I believe.  Other Quorn owners are using the same motor with no apparent issues other than a slow start. If change to a larger motor pulley I may bog the motor down at start up until it reaches full speed.  
I am trying to eliminate the need for pulley changes with the variable speed DC motor.  

Dick


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## British Steel (Nov 13, 2016)

Hi Dick,

you could use the KB controller you already have with a 90 / 180v DC motor, with the correct "power resistor" (which is in the motor return line, and senses the motor current) or, as you suggest, a 12v motor fed by one of the inexpensive EvilBay PWM DC motor controllers fed in turn from a transformer and bridge rectifier. A transformer for e.g. 1/4 HP at 12v needs to be able to deliver at least 15 Amps, so won't be small or particularly cheap - e.g. my suggestion of a thrift-shop start & charge battery charger (most of which will be happy delivering 15 Amps or more continuously - I use mine for allsorts, including the E.G.B.E.R.T. (Electrolytic Gungey Bubbling Encrustation Removal Tank - electrolytic rust removal!) with a 20A MCB on its transformer output - cheap way to deliver fairly hefty currents at 12v-ish.

I'm also planning a T&C grinder, but I have a 1/2 HP 180v DC motor squirelled away alongside one of the KBIC controllers, most of the DC motors of that type (e.g. those used in minilathes etc.) will run up to 5 or 6,000 RPM and down to a few hundred* so should suit a small T&C grinder pretty well in direct drive?
I wouldn't be so concerned with the motor bogging with a larger motor pulley, the inertia of a Quorn or similar spindle isn't all that much - the 1/2 HP motors on minilathes etc. cope with a much heftier spindle and chuck plus workpiece, if you have to wait a second or three for a T&C spindle to come up to speed is it a big deal? Anyway, if the motor can do the RPM you need, you shouldn't need the pulleys to speed it up much? Higher speeds will have the advantage of better fan cooling too!

Dave H. (the other one)

*it's worth adding an external fan, e.g. a PC cooling fan, if you'll be running at low RPM a lot, they tend to let the magic smoke out if they overheat! I like cooling fans, my rather-larger lathe has one on its motor so I can run it at 5Hz and get *incredibly* low speeds:


That's a 10 inch EBM Papst axial fan, yes, the motor's trashcan-size...


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## old toolmaker (Nov 13, 2016)

British Steel said:


> Hi Dick,
> 
> you could use the KB controller you already have with a 90 / 180v DC motor, with the correct "power resistor" (which is in the motor return line, and senses the motor current) or, as you suggest, a 12v motor fed by one of the inexpensive EvilBay PWM DC motor controllers fed in turn from a transformer and bridge rectifier. A transformer for e.g. 1/4 HP at 12v needs to be able to deliver at least 15 Amps, so won't be small or particularly cheap - e.g. my suggestion of a thrift-shop start & charge battery charger (most of which will be happy delivering 15 Amps or more continuously - I use mine for allsorts, including the E.G.B.E.R.T. (Electrolytic Gungey Bubbling Encrustation Removal Tank - electrolytic rust removal!) with a 20A MCB on its transformer output - cheap way to deliver fairly hefty currents at 12v-ish.
> 
> ...



Dave,

The AC motor I currently have on the Quorn is a TEFC motor.  No issues with overheating here.  But may be a different story when I convert to DC.  I will keep an eye open for a face mount 90 volt motor.

Dick


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## Tony Wells (Nov 13, 2016)

Good high amperage transformers can be found and salvaged from good sized UPS units. I have a couple that could do 20 amps easily. I believe they output 15 volts, open circuit. I'd have to measure again to be sure. It's been a long time and they are gathering dust.


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