modifying grinder speed?

[apox77]

I'm a newbie and was wondering if anyone knows how to make a foot pedal speed controller for a grinder. I've got an old Square Wheel (110v) and would like to slow things down but I would like it to be in pedal form so I can increase the speed while the knife is still in contact with the belt. I've seen some control units for sale but no foot pedals. I'm sure someone out there has some good electrical knowhow to make one relatively cheap.

Thanks

Apox77

 

[divewize]

good morning apox77

in order to have a variable speed control for a single phase motor
you first have to have a motor that can respond to variable voltage.

most single phase motors will not work with lower than namplate voltage as they rely on a capacitor to start and often enough to run on. a sewing machine motor is an example of a single phase non capacitor reliant motor that will work in a manner that you require.

the best way to get variable speed and maintain a constant torque capacity is to get a 3 phase motor (less $ than 1 phase)and put a variable speed ac drive on it. AC drives are available that can take a single phase input and provide a 3 phase output to a motor (bador machine does this).

unfortunatly its not a real Cheap way to go .
]

as for your foot pedeal deal

well a set up from a commercial sewing machine would work (motor/control) as for just foot pedals well , if you found a motor that will work with a reostat you can get a commercial use pedal but again pricey.

Id look for an old sewing machine...

hope this helps!

 

[Polock]

Well, yes and no.
In general if the motor was not designed for variable speed, it's not going to last long with any kind of controler.

An AC motor speed is more dependent on the frequency ( 60 Hz ) than the voltage (notice that the dual voltage ones run the same speed on both voltages) An "SCR" controler will work but one for a 1/2 hp motor or larger won't be cheap. You can slow one down some with a Variac but It will run hot.

If you feel you must have that much control over the speed, the best (and most reliable) soloution is to buy a new motor and controller setup made for variable speed. Either AC or DC. the electronic control unit uses a low volt/power reference circuit that may be adaptable to a foot control.

Please, don't post saying you can use a "potentiometer" This is a misuse of the term, A potentiometer is a variable resistor (a reostat is a heavy duty potentiometer). One big enough to control a 1/2 hp or larger motor will be big, expensive and could heat your shop. By itself it can only vary voltage and again, if it wasn't made for variable speed, the motor is in jepordy. Those who have had a good experience with jury rigged setups have just been plain lucky.

 

[divewize]

I have to agree with Polock an AC drive is the best bet and Jury rigs just get hot or dont work or dont work for long.

again with single phase you have to have a motor that is capable of variable speed, with single phase motor there are few and far between.


As for three phase motors yes their speed is controlled by variable frequency created by the controller but with the modern drives not only is the output frequency variable the output voltage varies as well which will provide full torque of the motor at any speed below 60HZ .

as for cost well a low end AC Variable frequency drive that is a chassis mount (needs to go in a box) the drive will run a 1/2 hp 3 PHASE 230v motor but only requires 110v single phase input. a low end drive like this starts at around $175.00

208/230 single phase input controlers are available as well but again the output is 3 phase.



a 1/2 hp 3 phase motor that will handle inverter service is in the $100.00+- range .

potentiometer foot pedals for the drives reference voltage are pricey they run about $125.00 + where as a 5k dial potentiometer can be purchased for as little as $20.00

DC controls are pretty inexpensive, there is a control from a company called KB electronics that is a basic DC drive and it sells for about $70.00 the only problem is what you save on a KB control you spend on a motor.

a 1/2 hp 90v armature permanent magnet motor is in the $200.00+ range.

6 in one 1/2 dozen the other . most folks these days are using the AC equipment.

like Dan blanton the salt water fishing writer says when it comes to equipmet buy once cry once but youll be happier.

again I hope this helps.

 

[Mike Hull]

Originally posted by divewize
a 1/2 hp 3 phase motor that will handle inverter service is in the $100.00+- range .


a 1/2 hp 90v armature permanent magnet motor is in the $200.00+ range.

6 in one 1/2 dozen the other . most folks these days are using the AC equipment.

Motors suitable for belt grinders used in knifemaking, usually start at 1 HP, and go up from there. Most seem to be in the 11/2-2 HP range.
A 1/2 HP might be usable for a finish disk grinder, but isn't powerful enough for a 2"X 72" belt grinder. It would bog down with any appreciable pressure.

Many knifemakers(including myself)use DC variable speed setups in their shops.

 

[divewize]

Hi mike,

sorry for the sizing info.

As for my statment most People are Using AC well I wasnt refering specificaly to knife making equipment I should have explained.

industry in general is moving away from DC equipment these days and opting for AC drives and motors
vs DC,IE: we converted all of the plastic extruders at one of the GE plants from DC to AC (100hp -732*hp (*custom motor) and many other companys have followed, the paper industry is pretty much using AC now a days where as 15 years ago sectional machines were all DC.

often enough when we have a customer that loses a DC motor or drive 9 out of 10 times they opt to retrofit with AC equipment.

My knife grinder from years ago was an old 110v single speed unit and had a "U" frame motor with no data plate HP ??.

Ive been out of Knife making for a few years but am dabbling again.

as for the DC grinder controls well up untill a few years ago AC stuff was too costly (mostly the drives)and AC did not provide enogh torque at slower speeds but the prices are comming down and the performance is now = to or in most cases better than DC .

Bader machine is now using AC stuff on their Larger 2-5hp variable speed units(AC tech brand ,we sell them to Bader) But I do believe they are still using DC (baldor) on the smaller grinders as You mentioned 1.5HP is the size, the main reason is cost ,mostly on the smaller sizes. the $175.00 is a price on a 1/2 hp Chassis mount AC drive but for a better 1.5hp single phase input control that puts out 230v 3 phase in a dust tight/ water tight enclosure the price is in the upper $400.00 range. actually bader will probably use AC on the smaller units when the pricing comes down a bit more .

anyway sorry for confusing anyone This is a great site lots of info.

"John"

 

[Mike Hull]

Yes, I agree with a lot of that.
AC is definitely less expensive overall, and the torque loss is minimal.

DC is a lot easier to setup, but is way more expensive to buy(new).