Delta Unisaw motor pulsating.

[Tom Howarth]

Last week I was ripping some 3"x6" Pine. Halfway though a cut, the motor started pulsating. I was pushing the boards slowly. I've never heard or seen anything like it. I was using a fairly decent blade. The saw is now working fine, BTW.
I was going to ask over at OWWM, but I can't remember my password.
Thanks for any ideas.

[lee cox]

How big is your motor? Do you think you were overloading it? Some of the old Unisaws came with 1/2 hp motors. Is your blade sharp?

My Unisaw has a 3 hp motor in it. In the couple of years I have owned it I have not seen a problem.

[Earl McLain]

I don't like cutting pine. Your blade may be perfectly sharp, but loaded with pitch. Even if you can't see it. Thin layer of sap really creates drag. Did a table late last fall, and ripping 9' 2x stock drove me nuts. A few of those were so sappy that I had to clean after each rip. Trend bit & blade cleaner works for me--others like different cleaners. I'll stick with cherry, maple, oak and walnut. Did I mention I don't like cutting pine??
earl

[Joe Kaufman]

If it is an older unisaw, it could have a repulsion/induction motor and a growling characteristic happens when the motor is overloaded and the motor slows down enough that it shifts from induction mode to repulsion mode. The mechanical mechanism that accomplishes the switch could also be out of adjustment, similar to a centrifugal switching a single phase motor. Just a guess.

[Mike Henderson]

Most of those old repulsion/induction motors were very low HP. Because of that, it was easy to overload the motor and slow it enough that the starting function (the repulsion function) would cut in. The repulsion function would provide additional power but would also draw excess current. The motor was not designed to work that way. The repulsion function is intended to be used only to start the motor, after which the motor is designed to run as an induction motor.

If used sparingly, it doesn't seem to cause serious problems, but when used to excess, the motor will overheat which will degrade its life. If the saw is underpowered, the best thing is to install a higher HP motor.

Mike

[Lee Schierer]

Considerably more information is needed. What size motor. What voltage. Have you checked the belts and pulleys? Perhaps a set screw is working out. Did the motor pulsate without load? Was the blade being pinched? What blade was being used?

It sounds to me like you were bogging the motor down with your 3" depth of cut and the belt(s) was slipping.

[Tom Howarth]

Lee,
its a ca. 1990 Delta Unisaw. 220v. I can't see the motors label. It came out of a school auction, hardly used, "Too dangerous for Middle Schoolers to use". Mostly used by Staff. I like your suggestion on the belts. I'll bet they are original to the saw. They seem to be a bit flexible, but not crunchy. No burning rubber smell.
The motor does not pulsate without a load.
ill have to track down some belts, any suggestions on where? Auto parts store? Or is the "V" in the pulleys different?
Back in my working days we would use belts from the same batch number, guaranteeing that they were all the same diameter...
Thanks to everyone for their replies,
Tom

[Jim Wheeler]

If it is a single phase motor, there is another possibility: Some of the later model Unisaws achieved their rated horsepower by using two capacitors - one for starting and one for running. If the running capacitor is weak or going bad, the motor will not be able to develop its full rated horsepower continuously under heavy loads. I would check both capacitors before I'd replace the motor.

Jim

[Lee Schierer]

Back in my working days we would use belts from the same batch number, guaranteeing that they were all the same diameter...
Thanks to everyone for their replies,
Tom

The belts may not be tensioned properly. Any good industrial power drive supplier can get you good belts. Modern drive belt making is far more precise and you don't need to buy "matched" belts. I recommend Gates.

[Mike Goetzke]

Could it be the wood?

Mike

[lee cox]

The belts I used in my 1950 Unisaw were Gates AX-24 belts. These are really nice belts and you don't need to match as they are all precisely made. I ordered my Gates belts from O'reilly's auto parts. They were about $7 each.

[Charles Lent]

The belts for my mid 80's Unisaw came from www.ereplacementparts.com as a matched set. I believe that they still sell them.

Charley