Table saw vibrations on startup / shutdown (video inside)

[Steve Dublanko]

I just got my new General International 50-270 (3HP 220V) table saw set up (a big thanks to all that helped me make this purchase!) and I have a few questions with regard to motor vibration.

My saw has some pretty good vibration on startup and especially shutdown. During normal operation it is very smooth. I did a little research on this and even called tech support at General. They told me that it was perfectly normal and is due to the torque the motor puts out. I have checked the pulley's, belt, arbour and blade and everything feels very smooth (no play / wobble anywhere).

I've seen many videos of successful nickel tests (including startup / shutdown) and there's just no way mine would pass this on start / stop. I thought I would put my mind at ease and post here as a double check.

Here is a video demonstrating the vibration.

Is this something I need to worry about?

Thanks!

[Mikail Khan]

No. Enjoy the saw.

MK

[Bill White]

BIG worry about the small stuff. If it cuts, you're ahead of the game.
Start up and shut down vibs are kinda normal on mine. The saw does a really good job when running at speed.
Bill

[Steve Dublanko]

Hi Bill,

I'm not too worried about it. I more or less just wanted to know if that kind of vibration is normal -- particularly on shutdown. There is a rather loud thunk that seems to happen as the motor spins down.

[Steve Dublanko]

Thanks Mikail.

[Yonak Hawkins]

Steve, that [thunk] does seem rather unusual to me, but I am by no means an expert. It could be due to belts (maybe not tight enough (?), I really don't know) that get to a certain harmonic vibration at a point. You could look at the belts and see if they really fluctuate at that moment. However it would concern me enough to take the video to the store that sold it to you for an explanation. If they say it's normal, at least they have seen the evidence if you should have, say, bearing problems in the future.

[Randy Heinemann]

Viewed the video and it didn't sound like there was any significant vibration. I don't have the saw, but have an 8" Jet jointer with a 220V 2HP motor and the start up and shut down are noisier on my jointer. To start my motor there is a noticeable thunk and some vibration for a brief time till the motor is up to speed. Then, on shut down, there is some vibration just as the motor slows to stop. From the video it doesn't sound as if there is a problem. If there is a problem it will likely show up during the warranty period anyway.

[Darcy Warner]

That's all to do with the single phase motor.

[rudy de haas]

hi:

I have a Craftex cx-08 (cdn version of grizzly G0490) 8" jointer that has pretty much the same thunk - runs nicely, but stops loudly. The reason it does that is that is missing the extra spring loaded arm and pulley that dampen belt vibrations during start-up and shutdown. Mine was the shop floor model at a busybee (griz) store in Calgary, and is from the generation before that was installed as standard. I may decide to add it later, but since I hardly use the thing it's not seemed important to me. On the other hand, if the saw sounded like that, I'd panic...

[lee cox]

It looks like it runs smooth. Maybe there is a brake in the motor on shutdown to stop it quicker. I would just in enjoy your new saw and not worry about it.

[Steve Dublanko]

I've been doing a little more testing and it seems like a relay triggers a motor break when the saw spins down.

Here is a video of the saw without a blade.

The vibrations are greatly reduced, and the "thunk" is not really there -- just sounds like a relay switching.

For comparison, here is one with the blade and guard on.

The thunk is disturbingly loud to me, as is the vibration. Arg.

[Mikail Khan]

Is the belt tensioned properly? Try with belt off. See if belt has a "set". If so a link belt may help.

MK

[Mikail Khan]

Ensure pulleys are tight on shaft and motor is properly bolted up.

[scott spencer]

It's worth checking that the pulleys are tight, but is probably nothing to worry about, and is relatively common on saws with that type of motor setup. It's likely from a phenomenon called regeneration caused by the capacitors when the centrifugal switch cuts out at shut down. There are some ways of shunting the caps with resistors to remedy it but I don't know what values you should use, and don't think it's worth any time and effort if the saw runs and cuts well otherwise.

[Steve Dublanko]

HI Scott,

I believe you are correct. I've just spent an hour or so reading about how these motors work and it is very common to have a centrifugal switch change the operation between two wingdings (usually a start winding and a running winding). When the saw slows down, the switch re-engages the start winding and you get the regeneration effect that slows the motor down considerably. You can see it quite clearly in the video without the blade on -- you can hear a "click" and then immediately you see the screw threads on the arbour indicating that the motor has slowed down considerably. When the blade is off, you don't hear the "thunk" because there is no rotating mass slowing down.

I checked the pulleys and they both seem tight and move cleanly. One thing to note is that when you spin the blade manually there are definitely smoother and rougher spots in the rotation. This is probably caused by having a brand new belt that is not yet broken in. Could this be the reason for the vibration as the saw slows down (after the "thunk")? Would a broken in belt reduce this problem? I guess I could try playing with the belt tension a bit to see if that helps. I haven't tried running the motor without the belt but I suspect I wouldn't get any vibration and that I would simply hear the "click" of the switch slowing down the shaft on the motor.