MIMF

Hi folks,

My ancient table saw stopped working today while I was ripping some floor boards. It ran fine for 5 or 6 boards, but then when I went to turn it on the last time, it tried to run for a split-second then died. Since then I can't get it to do anything. The pulleys will turn, so I don't think it's' frozen up, and I don't feel any difference in the feel of the bearings. There's no humming or anything when I hit the switch. As far as I know it hasn't thrown the breaker. There's a red button on the back side of the motor, which I thought might be some kind of reset, but it doesn't feel like it's doing anything if I press it. Any ideas?

Thanks,

dw

is it single phase or three phase? I'd check the plug on either, but I've had three phase motors start to start and then stop because the plug is loose or dusty. I'd say pull the plug, blow it out if it's dusty and plug it back in. 90% of the time I've had this problem that's been the cause.

Hi Dan;
Couple other things that might be worth a try. Unplug the saw and (depending on the type of switch it has) take the cover plate off the switch and blow/clean any dust out. Also blow any dust out of the motor windings if there are cooling vents. My old sears TS has a funky old motor that dust gets inside of and it won't start. Blowing the dust out does the trick!
Good luck.
John

Sounds like a start capacitor to me. It could also be the switch. Particularly if it's an old switch. Contacts may be burned out. I had an old high speed grinder do that, although it burned out in the on position. Couldn't turn it off.

First things first; check the power source. If there's power at the outlet (assuming it's plugged in, not hard wired), check for power at the switch and continue along the circuit.

Waddy Thomson wrote:Sounds like a start capacitor to me.

Except that he said it doesn't hum or anything. Every time I have had a capacitor problem or seen someone else have one, the major symptom was humming. I think you might be right on your other thought (switch).

Unplug the saw and (depending on the type of switch it has) take the cover plate off the switch and blow/clean any dust out. Also blow any dust out of the motor windings if there are cooling vents.

I've done this too (successfully).

Hey guys, thanks for the advice. I blew dust out (the little compartment on the back end was packed with it), checked connections, all that, and it still wouldn't run. John, I think you hit the nail on the head this time. Boy is my face red -- as far as I can tell, the saw is fine, I just blew up the little outlet strip I was running it through. The light on it came on, so I figured it was functioning, but apparently there was no juice getting to the outlets. Since I was fiddling with the saw anyway, I decided to go ahead and replace the main power switch (the 1960's-era push-button light switch it came with) with one of those big paddle switches with dedicated on and off buttons. Now that I can make sure it's *off* before plugging it in, there's no need to put the outlet strip in the circuit.

On some older electric motors there is a set of contact points for the starting circuit and saw dust can get in them and cause this symptom. Blowing out the dust is the cure but you may have to open the plate on the end of the motor to have good access to the contacts. This is where a TEFC (totally enclosed fan cooled) motor is appropriate.

Dust on the contacts is exactly what happened to me in the same circumstance. I have a 25 year old 10" Craftsman contractor table saw that has served me very well. But one day, it just wouldn't turn on. I ended up getting a blower adapter for my compressor and blew it through the motor openings and it's been working perfectly since.

Chboswell wrote:Dust on the contacts is exactly what happened to me...

Hi Chboswell,
Please note that we require the use of real full (first and last) names on this forum, and do not accept aliases or "handles". Please let us know your name here or in a private message so we can update your registration and login details for you (you are not able to make these changes to your account yourself).
Thanks.

A lot of motors have a small molded sheetmetal cover on the side of the motor. It may be about 3 inches long. Inside is a "capacitor". The motor gets extra power from that capacitor to start up.

They go bad once in a while. Pull the cover off, expose the leads on the cap, and short the leads together with an insulated screw driver or wire cutters. ***BE CAREFULL*** it -could- be charged, and if you touch it, it will ruin your day... This is why you want to short the leads together while holding an insulated handle... After shorting the leads together, it would discharge and be perfectly safe to handle.

Look at the number for the rating of the cap. It is probably 5uf, 7.5uf or 10uf. There are other sizes out there. It will also say 370 or 440.

I dont remember how exactly to test one with a regular multi meter... Remove one lead, and use resistance on both prongs, you should see the resistance climb, then drop off again??? something like that... easy to find on the net I'm sure... My multi meter is specifically sold for air conditioning technicians it actually has a cap tester built in... I pull one lead set the meter to capacitor, and it will display the actual capacitance.... if its supposed to be 5uf, it would read "5.00" with my meter.

If the cap is bad, you should be able to order one on the internet. Just be sure you have the right uf, and 370 or 440, AND GET THE SAME FORM FACTOR. Most of the ones on table saws are round, but very small. "oval" is very common for air conditioning motors and will not fit into that sheetmetal holder. Though it would work correctly for the functionality of the motor itself.


Pic shows you the capacitor cover.