Is it possible to reverse the rotation of a radial saw motor?

[boyntonstu]

Just wondering whether it could be done.

[Martin H. Eastburn]

If it is 3 phase, swap two of the power wires.

Otherwise the motor might have cw and ccw shades and it is a mater of re-wiring. Takes specs of that motor and knowledge.

Mart> Just wondering whether it could be done.

[Andrew Erickson]

At least a few radial arm saws (Wards Power Kraft for one) use/used universal motors, wherein swapping the polarity of the rotor relative to the stator ought to reverse the motor. One obvious way to do this on such a motor is to swap the connections to the brush leads.

I do sincerely hope the original poster isn't intending to use the radial saw in reverse; that sounds like a recipe for disaster. I suppose if one wanted the blade on the opposite side of the traveler one would need to reverse the rotation of the motor (and probably reengineer the mount some), but otherwise...ouch.

[-MIKE-]

I've always wondered the same thing.

[Martin H. Eastburn]

When I got my Delta Band saw - it came from a good dealer in a state. The manager was at a conference and the guys shipped a bandsaw and a motor. The motor had sawdust on it and wasn't in a new box. Hum - stripped it off something. Looks new.

I installed it and the saw ran backwards. Just like a lathe.... I swapped the wires as mentioned - inside it was marked - and then the saw cut wood. I then converted it to 14".

So wood working motors as others reverse.

Martin

-MIKE- wrote:

[clare]

Some do, some don't - and some are unpredictable. A good friend has a nice radial arm saw from the 60's -can't remember the manufacture (deWalt, perhaps?)r but it's hammertone green - and it will occaisionally start backwards - but worse yet, if it jams it WILL reverse. It will throw sticks with a veangeance given half a chance!!!!!

[dadiOH]

Strange, I've spent my life NOT wondering :)

[Robatoy]

It is just when the blond swedish twins start unbuttoning their tops that the question about motor reversal rears its ugly little head.

[Jay Giuliani]

Don't believe so.

It is an AC motor and will rotate with the field.

If it was three phase it could be done.

Why??

[Leon]

Yes, Turn the motor and blade unit 180 degrees so that the blade is located on the opposite side.

[Steve Turner]

It's good that I've learned to set my coffee down before reading anything posted to this group. Out through the nose is no place to send a big slurp of hot coffee. :-)

[Tim Douglass]

Cleans and sterilizes the sinuses to prevent infection.

Tim Douglass

"I'm not exactly burned out, but I'm a little bit scorched and there's some smoke damage."

[dadiOH]

I feel your pain in my waking state, other things when asleep :)

[Steve Turner]

Yes, I hope the idea isn't to simply reverse the blade and do crosscuts in the same manner as before! Apart from the saw throwing all the sawdust in your face, the blade would be trying to force the wood *away* from the fence, causing binds, kickback, and other unfortunate side effects such as injury or death.

[whit3rd]

As others have noted, you might be able to swivel the sawhead 180 degrees (would only be safe if you also repositioned the fence to the far-from-column side of the work).

Electrically reversing the motor is probably psosible (usually these have brush-style motors, you could reverse the brush polarities); the gears, however, would NOT necessarily mesh neatly with the newly reversed drive, and some kinds of spiral-cut gears could cause the blade position to destabilize.

[Tom Veatch]

I assume this is an AC motor. Don't the brush polarities reverse 60 times per second already? Or possibly I'm not understanding what you're saying?

Tom Veatch Wichita, KS USA

[Andrew Erickson]

They do indeed reverse 120 times per second (60 full cycles per second), but so does the field coil, so the relative magnetic polarity of the one with respect to the other stays the same. In other words, the repulsion or attraction of the two doesn't change. By swapping the brush connections, the magnetic polarity of the rotor with respect to the stator is reversed and the motor forced to turn in the other direction.

Motors of this design are often termed "universal motors" because they will operate properly on AC or DC current, and furthermore are not particular about AC power frequency. My RAS with such a motor is specified as being for either 25Hz or 60Hz AC; I assume 50Hz would also be OK. DC is presumably not listed because of the power switch being insufficient to properly cut off high DC currents, not because the motor would fail to work properly.

[Tom Veatch]

That's the way I understand it and I won't quibble on whether it's 60 or 120 time/sec. Kinda depends on the definition of "reversing". So "reversing polarity" of the brushes - which I interpret to mean switching leads - won't have any effect on rotation direction of a universal or any other type of AC motor. That would be no different than reversing the plug in the wall socket.

On the other hand, breaking the motor open, and doing some internal rewiring might accomplish the mission.

Tom Veatch Wichita, KS USA

[Andrew Erickson]

Switching the leads to the brushes generally does require breaking the motor open and rewiring it internally a bit. It's not the same as reversing the plug in the wall socket (which, as you correctly observe, would have no effect on the direction of rotation). Swapping the input leads changes both the field (stator) and the rotor, and so the rotation stays the same. Swapping the brush leads changes only the rotor, but leaves the field unchanged, so the relationship between them is reversed.

Here's the a link to a quick schematic sketch of this operation on a series wound motor that might make things a bit clearer:

[Jay Giuliani]

If it is a single phase motor it won't reverse.

Think about all those two prong corded ac 115 VAC tools......

You can reverse rotation on a three phase mpotor but as the other folks said, why?