Table Saw Noise

[Chris Leacock]

I finally got a chance to fire up my PM66 for the first time last night and I noticed something that didn't quite sound right to me.

There seemed to be some sort of intermittent rattle while it runs. Actually, it's more like an audible vibration than a rattle and it's pretty consistent; on for a second, off for a second, on for a second...etc. Almost like it's keeping time with itself.

Prior to turning it on I made sure the blade was aligned with the miter slot, aligned the faces of both pulleys and made sure the belts were tight (although I have no idea how much tension they should actually have).

Does anyone have any idea about what could be causing this sound and what I should start looking for? Or is it normal?

Just as an FYI, I didn't run it very long nor did I have time to really listen for where the sound was coming from. As I was cleaning and tuning it up I did notice that when I hand-turned the arbor, there was a spot where it got a little more difficult to turn and then it eased up again.

Also, when I removed the belts they pretty much stayed fairly oval as opposed to round. Don't know if that means anything but thought I'd mention it.

As always, thanks for your help! I've learned a ton from this forum already!

[Loren Hedahl]

It will be interesting to see what this finally turns out to be.

For myself, I'm always a bit paranoid when trying out something new and expensive for the first time.

Just thinking, it could even be an audible interaction of the motor frequency with the buzz of fluorescent lights in the area.

The reason for this is the motor runs at a calculated "slip", that is -- it rotates slightly slower than synchronous with the 60 HZ power input. As the motor is loaded it continues to rotate slower, i.e., slip more until reaching its maximum developed power rating. Most two pole motors are designed to rotate at 3450 RPM at full load with a 60 cycle input (equivalent to 3600 RPM at zero slip). With no load on the motor, there will still be a slight amount of slip due to the loading of bearing friction and blade windage. This slight loss of speed might be just right to cause audible peaks and nulls with the lighting buzz.

Pretty good, huh? I should at least get an "A+" for armchair troubleshooting!

[Greg Karol]

it could be that your arbor bearings have gone bad. Take off the belts and spin the arbor with your hands. Do you feel/ hear that noise? If so you will need to replace those bearings.

[Mike Goetzke]

I did notice that when I hand-turned the arbor, there was a spot where it got a little more difficult to turn and then it eased up again.

Also, when I removed the belts they pretty much stayed fairly oval as opposed to round. Don't know if that means anything but thought I'd mention it.

As always, thanks for your help! I've learned a ton from this forum already!

When you turned it by hand and found the more difficult spot did you have the belts on? If so, my saw does the same thing due to the belts not being round.

Is you belt tension correct? Does the saw seem to vibrate with the sound?

Try removing the blade then the belts and re-running to see if you can isolate the problem.

The sound you describe is a vibration resonance - could be cause by many things.

Mike

[Tom Veatch]

... Actually, it's more like an audible vibration than a rattle and it's pretty consistent; on for a second, off for a second, on for a second...etc. Almost like it's keeping time with itself.
Is it a hum, or does it sound "metallic". If a hum, it's either electrical like Loren mentioned, or some natural frequency of the saw's structure that's being excited by motor vibration. In either case, you're describing a beat frequency - two or more audible vibrations with slightly different frequencies that alternately reinforce and cancel each other. Unless it's metallic and harsh enough to indicate two pieces of metal banging against each other, it's probably not worth worrying about.

Prior to turning it on I made sure ... the belts were tight (although I have no idea how much tension they should actually have).
My 'rule of thumb' for V-belts is tight enough that moderate finger pressure at the center of the free length between pulleys deflects the belt about 1/2". They really need to be no tighter than necessary to prevent slipping at the maximum torque of the motor.

Also, when I removed the belts they pretty much stayed fairly oval as opposed to round. Don't know if that means anything but thought I'd mention it.
Not that unusual. V-belts tend to take a "set" after being installed and tensioned for a period of time. That's one reason "link" belts frequently reduce vibration.

[Chris Leacock]

Okay, here's what I found out last night.

I turned the arbor by hand with the belts on and it seemed to "rub" at about the same point every turn. (It's a metallic sound.) So I took the belts off and turned the arbor again. No sound this time and it didn't rub. I also reached in further and turned the motor pulley by hand. I didn't get any rub there either.

Could it be that I really don't have the pulley faces in line with each other? Regarding the belts, something I noticed last night was that they are a different shape when they're off. Maybe only one was replaced instead of both?

Since I wasn't able to get back to it until after my 3 year old was in bed I wasn't able to run it with the belts off. (Her bedroom is right above where the saw sits.) So I'll have to do that tonight.

[Josiah Bartlett]

I suspect your belts have taken a set. They probably tend to stop at exactly the same place, and you will feel them fight you as you turn the arbor with them installed.

[Lon Schleining]

You mentioned aligning the pulley faces. Are you sure you re-tightened the set screws when you finished messing with them?

Also a good industrial supply will sell matched sets of belts. Might be worth a look. That said, I just a couple of months ago replaced the original belts on my PM 66 after a mere 25 years of daily use in a professional shop. Darned cheap belts anyway!