Humming Table Saw-Dangerous Saw

[Dan Friedrichs]

but most likely the start button is too close to its contacts and any little bump and it touches and completes the circuit.

But how does this explain the humming when the contactor is open? I suppose the start switch could be dirty and making a high-impedance circuit through the coil, causing it to hum but not quite get enough current to pull the contactor in, but geez, that would seem to require some precision dirtiness, wouldn't it?

I wonder if there is an alternative path for the coil current. Possible that the cord is frayed and one side is shorting to the chassis? Or the switch is slightly to large for its enclosure, allowing a contact to touch the chassis? That seems more likely to explain how bumping the saw triggered it - wiggled a wire against something, momentarily.

I'd carefully inspect all the wiring. Then, ohmmeter everything out to confirm nothing is shorted. Then, I'd hook up the switch to power WITHOUT the rest of the saw, and see if it hums (it shouldn't!). Then, connect the motor (ideally not using the wiring in the saw). Etc. I bet you'll find a wire that's been rubbed through, somewhere.

[Ron Selzer]

Time to take it to whoever Rigid wants to check it out. Send copy of video with it
Liability is too high for you and Rigid at this time.
Ron

[Mark Hennebury]

If it were me, I would take the switch apart and check it. check the contactor points to see if they are burnt, they may be fried and not making full contact, or not separating properly, check the switch contact points, clean any dust and dirt out, make sure the springs are in good shape and functioning and the switches move freely. check the contactor springs and movement, You will probably see what the problem is when you get the switch apart. Take a few photos of it when you get it apart.

But how does this explain the humming when the contactor is open? I suppose the start switch could be dirty and making a high-impedance circuit through the coil, causing it to hum but not quite get enough current to pull the contactor in, but geez, that would seem to require some precision dirtiness, wouldn't it?

I wonder if there is an alternative path for the coil current. Possible that the cord is frayed and one side is shorting to the chassis? Or the switch is slightly to large for its enclosure, allowing a contact to touch the chassis? That seems more likely to explain how bumping the saw triggered it - wiggled a wire against something, momentarily.

I'd carefully inspect all the wiring. Then, ohmmeter everything out to confirm nothing is shorted. Then, I'd hook up the switch to power WITHOUT the rest of the saw, and see if it hums (it shouldn't!). Then, connect the motor (ideally not using the wiring in the saw). Etc. I bet you'll find a wire that's been rubbed through, somewhere.

[Bill Howatt]

Mark, she apparently has the humming concern, valid or not, with the replacement switch. I don't think she has tried the bump test with it though.

[Dan Friedrichs]

Mark, she apparently has the humming concern, valid or not, with the replacement switch. I don't think she has tried the bump test with it though.

...which is why I'm leaning towards a frayed wire or something like that.

[Warren Lake]

have had this past. Move the little 8" jointer just drag it from a table and it starts. After shut off got to start a few more times from thumping. Then last year the compressor kept running and running then was okay then days later would not shut off. The two parts that slap together when you push start were welded together. Switch over 40 years old. The problems I had past were Brooks Crompton Parks switches and I used to take them apart file the contacts and they then worked fine but a few times little springs shot across the room and so much for that. Then I went to Danfoss switches and have had the best luck with them.

[Mark Hennebury]

Sorry wasn't paying attention. If the new switch is humming, like Dan said, maybe a frayed wire, or the contactors are not making proper contact would be my guess, maybe just the switches are faulty.

Mark, she apparently has the humming concern, valid or not, with the replacement switch. I don't think she has tried the bump test with it though.

[Diane Barker]

Thanks for all the input everyone. I have emailed Ridgid last night and will update this thread with whatever they reply.

[les winter]

A contactor enclosure full of saw dust will do this.

[Dave Roock]

This is not actually a problem that needs the hassle, time and expense of repairing at all. The solution is a change in procedure - get a short stout power cord with an on/off switch. Plug the saw into this power cord. Leave the saw power always on but have the power cord on off. The saw will never turn on like that again. You have to typically turn the power on the saw - this way you do the same with the power cord switch.

[Bill Howatt]

Actually, you would have to turn the power cord switch and the saw switch on. The saw has a magnetic type switch that goes to the off state when the source power is removed.

[Dave Roock]

Actually, you would have to turn the power cord switch and the saw switch on. The saw has a magnetic type switch that goes to the off state when the source power is removed.

Okay the problem would be solved with only the addition of on extra switch turned. With no power going to saw, problem cannot re-occur.

[Malcolm McLeod]

... It hums sometimes when its plugged in. ...

Some disclaimers: 1, I've not owned, used, or worked on this saw. 2, Its beyond tough to diagnose electrical problems over the internet. 3, I'll try anyway.

The humming likely originates in either a control power transformer or the coil. Both generate a magnetic field and so are prone to vibrating (a hum). I doubt a saw marketed for hobbyists has a transformer ... that adds $$. I'll have to assume the saw has a magnetic contactor as others have stated.

Taken together, this leads me to suspect the coil is getting some voltage bleeding into it (while it hums) - - enough to generate some magnetic field (and hum), but not enough to engage the main contactors. When you physically bump it, there is/was enough combined force to fully engage the contactor.

Since the switch replacement seemingly didn't fix it, I'd start with a meter and determine if and how much voltage is applied to the coil when it's humming, then trace that to a source - - maybe a short?

Or, possibly the holding contacts are carbonized/burned enough to allow some voltage to bleed through? If you push the stop button while its humming, does the humming stop?


Good luck and please be careful.

[Rod Sheridan]

Hi Diane, yes that’s extremely concerning.

The literature I’ve read says the saw has soft start circuitry to ramp up motor speed when starting.

That leads me to believe it has a solid state starter, if so as an electrical technologist I would never approach the blade area unless the saw is disconnected from power.

The above is always a good approach, my saw has a convenient disconnect switch for that purpose.

The humming may be leakage current through the starter, or a control power transformer noise. If it’s the transformer that’s nothing to worry about.

Can you take apart the old starter and post photos please?

Regards, Rod

[Brian Holcombe]

Route the wiring through a rotary disconnect and give yourself some redundancy in this aspect of safety.