Thread: Speed control for induction motor

Use a coolant

Use a coolant

What he said, also try a tool cutting compound.

Ther's no easy and economical way to slow an induction motor Glenn

You need to drop the voltage- eg if the motor os 240V AC, and you drop the voltage to 120V AC - the motor will work half as fast.

best for a sparky or engineer to do this for you. If you familiar with AC theory you may be able to work it out (and a practical solution) yourself but I would be concerned for insurance purposes.

as an alternative to voltage dorp or cooling compound what about a gear reduction pully system on the chuck ????

If you can easily replace the pully on the shaft of the motor or the shaft of the drill spindle (or both) that might be the go. You need a smaller one on the motor shaft and a larger one on the spindle.

Zed,

The AC "squirrel cage" motor used in drill presses will NOT drop to half speed if you halve the input voltage. Speed is contolled by mains frequency and the design of the windings.

If you drop the voltage, then load up the motor, it will pop its cork.

Ed T

AAARRRGGHH!!! DC theory - dontcha love V=IR ?

Rev - Doesnt an induction motor not have pulleys ? I thought the speed was goveredn through a potentiometer in the windings .... thats why I suggested pulleys in the chuck....

Zed,
I think almost all drill presses use induction motors and most are driven via pullys and belts (some in steel engineering workshops are driven by gears and shafts). Anyway, larger pullys on the spindle and smaller pullys on the drive shaft of the motor combine to reduce the speed of rotation of the drill I think.

This doesnt alter the speed of the motor, just the speed of the drill.

Originally Posted by glenn k

I need to slow my drill press down to 180rpm to countersink 1/2" holes in spring steel to make blades. On the slowest speed it is too fast is there an easy way to slow a 1/2 hp induction motor? I did make a tungsten drill bit to do the job but it is slow and gets hot so I think it would be better to slow the drill down and use a proper countersink bit.

Glenn ,is your spring steel softened where you are trying to countersink?If it is still hard (the spring steel)I would use a dremel ,or the like and grind the countersink.
On the other hand ,you may know something I don't ,please tell how
you doing the countersinking(please forgive the pigin)and what bledes are you making.
Regards Bela.

I'm using roil as a cutting compound it worked well to drill about 20 1/2 " holes though 8mm spring steel to the sharpen. The countersink bit is bigger and needs to go slower.
Bela it is new spring steel that has not been hardened. If it gets hot it hardens. When cutting it to length it got hot a few times and the cut off wheel had trouble getting through.
I blunted a countersink (cobalt HSS)bit in one go $60 worth I took it back and paid another $15 to replace it with a titanium coated one and was told to run it at 180 rpm. The tungsten carbide bit I made works but I feel the drill is too fast. The blades are for a 9" wood chipper.
I was hoping there was something available to remove every second peak from 50 Hz to make 25 Hz so have a motor with half the speed and half the power but it appears there is no such thing. I may have to add an extra pulley shaft but a very large pulley on the chuck shaft may be easier.
Thankyou for the input every one.
Glenn

most of the variable speed portable drills can spin very slow, might be the way to go.

Originally Posted by glenn k

I'm using roil as a cutting compound it worked well to drill about 20 1/2 " holes though 8mm spring steel to the sharpen. The countersink bit is bigger and needs to go slower.
Bela it is new spring steel that has not been hardened. If it gets hot it hardens. When cutting it to length it got hot a few times and the cut off wheel had trouble getting through.
I blunted a countersink (cobalt HSS)bit in one go $60 worth I took it back and paid another $15 to replace it with a titanium coated one and was told to run it at 180 rpm. The tungsten carbide bit I made works but I feel the drill is too fast. The blades are for a 9" wood chipper.
I was hoping there was something available to remove every second peak from 50 Hz to make 25 Hz so have a motor with half the speed and half the power but it appears there is no such thing. I may have to add an extra pulley shaft but a very large pulley on the chuck shaft may be easier.
Thankyou for the input every one.
Glenn

Thank's for reply -explanaion Glenn.
Regards ,Bela.

If all you want to do is drop the speed you can use a heavy diode in series with the ac feed. This will feed one half only of the sine wave AC to the motor and effectively be 25 hz., hence approximately half speed! You will have to use a diode with ample current rating (amps) and a voltage rating of at least 600 to 700 volts. Bear in mind that the available power will also drop to a little less than half. Better to play with pulleys. Cheers. Les.

Originally Posted by glenn k

I was hoping there was something available to remove every second peak from 50 Hz to make 25 Hz so have a motor with half the speed and half the power but it appears there is no such thing.

Glenn,

If you are half handy with the soldering iron, go down to Dick Smiths and pick up a motor speed controller kit (you'll have to put it together). The way this works is quite sophisticated, but basically allows infinite speed control whilst maintaining torque and smoothness of operation (if you start chopping the wave forms you can get jerky action).

I have used one of these on my 3 hp router with great success.