Humming Table Saw-Dangerous Saw

[Diane Barker]

Hello All,

I have a Rigid jobsite saw in my shop. It hums sometimes when its plugged in. Not always, just sometimes. None of my other electric power tools hum. But I thought maybe that is normal. I have had it two years. Well...something sickening happened this fall when I was ripping boards for soffits. The saw, upon tapping so lightly to move the fence a sixteenth of an inch, turned on by itself. It makes my stomach turn to think of all the times it could have taken my finger off when I do the things I do while the saw is plugged in, such as simply measure with the tape to see about distance between fence and blade. I can think of a ton of ways this saw could hurt someone unless you plug it in, rip, unplug it....every....single....time.

I contacted Rigid. The tech support woman was a bit concerned, she said it sounds like more than the switch. Asked me if I could catch the hum on video, which I did. They sent me a new switch. I just installed that new switch. I plugged it in, and it hummed, then stopped. I turned it on, it worked, turned it off and it hummed again.

What should I do? This saw is a liability to anyone working around it. I will contact Rigid again, but wanted some advice from you all.

[Bill Howatt]

I looked at the manual for a R4514 Ridgid jobsite saw and it describes what is normally called a magnetic switch to control the motor - the clue is it says that if the power is interrupted you have to press the ON button to get it to go when the power is restored. Humming is likely from the magnetic relay coil in the switch and itself isn't a real concern, I think. What you described about the saw turning on when you bumped the fence is, unfortunately, a problem with some magnetic switches although it doesn't seem to be as frequent a complaint now as it was with some older ones.
What happens is that the bump vibration can cause a very brief momentary closing of either the On pushbutton contacts or more likely, what is called the relay sealing contacts on the contactor that provides the power to the motor. The sealing contacts are needed to keep the contactor turned on when you take your finger off the ON button.
Perhaps, the replacement switch is better than the old one so give it a few whacks although the fact it did happen does mean you should not work near the blade with the unit plugged in. I don't have this arrangement on my saw but I always unplug it when switching blades or similar activity near the blade.

[Diane Barker]

Thanks for that input Bill. Very helpful. I can understand what you are saying. The only thing is...do I unplug it every time I am finished with the cut in order to keep everyone safe? Even to just do something like tap the fence over a half inch with my tape in my hand near the blade? I have talked to my wood working buddies here in town and no one has ever heard of a saw going on from a tap on the fence nor do their saws hum. My concern is the humming means the saw is in super sensitive mode and any movement might turn the saw on. I just wrote back to Ridgid and we will see what they say. But for now, it is kind of frustrating to have to be so vigilent around the thing.

[Larry Frank]

I would not even consider using the saw until this is fixed 100%.

The risk is too great.

[Robert Hayward]

I would not even consider using the saw until this is fixed 100%.

The risk is too great.

+1. That is way too dangerous to even mess with. Just one absent minded touch while plugged in could remove body parts.

[Lee Schierer]

I don't know much about magnetic contactor type switches. Yours sounds defective or miswired. Maybe replace it with a regular on/off switch such as this.Screenshot 2024-02-11 202720.jpg

[Bill Howatt]

I'm curious if the new switch starts with a bump. If it does there is a design flaw or a bad batch of switches. The humming is strange and normally there is no power to the contactor coil until the On button is pressed so it shouldn't hum. However, if there is a low voltage transformer in the box it could be humming. Is the humming from the switch box area or the motor itself?

[Diane Barker]

Hey Bill. Just looked at it again and it seems the hum is from the switch. But cannot be absolutely sure as sometimes the hum is loud and sometimes softer.

[Richard Coers]

Alleviate some angst. Unplug the saw when you are not cutting, including during a setup.

[Mark Hennebury]

A basic magnetic switch circuit has two circuits, one power circuit and one control circuit.
The power to for the motor goes to L1,L2,L3 in a three phase circuit.
The control circuit is A1, A2, they may be a different voltage. They control the electromagnetic coil
As you see in the diagram, you have a momentary start stop switch.
Press the normally open start button, that completes the circuit to energize the coil, and that pulls the contactors closed to start the motor. It also allows power from A2 to flow through the contactor to keep the coil energized when you let the start button go.
This keeps the contactors closed and your motor running, once you have taken your finger off the switch.
To stop the motor you have to break the circuit by pressing the stop button. That breaks the power from A2, and resets the switch.

What must be happening in your switch is that when you tap the fence the start button must make contact to start the sequence. It could be the A2 contactor making the contact, but most likely the start button is too close to its contacts and any little bump and it touches and completes the circuit. you could probably just check the start button and clean it and make sure the button is moving properly and that the spring is pushing it away from the contacts.


magnetic.jpg

[Brian Holcombe]

Personally, I have E-stops on every machine and if I’m changing tooling, or otherwise touching the blade, I will always engage the emergency stop and sometimes also disconnect the machine using the rotary disconnect. I’ve had a few machines with weird start/stop switches and in those cases I remove the switches and build out a new start/stop unit which is uniform with most others in the shop having a standard push button start/stop and an E-stop.

[Alex Zeller]

I would contact Rigid again and explain the switch didn't fix the problem. Is there a repair center near you that Rigid could have look at the saw? If so I would request having that place identify the problem and fix it. You could have a short that's intermittent or has just enough resistance so there's just not quite enough power to pull in the magnetic switch. Adding an extra kill switch isn't a bad idea but if it was me I would want it fixed correctly. But I deal with repairing electronics and electric equipment so troubleshooting the problem is in my wheelhouse. Unless you feel confident that you can fix it the worst thing you can do is think it's fixed and let your guard down.

[Ken Fitzgerald]

I agree it sounds like a electro-magnetic contactor is defective. I have seen solenoids where the contacts become pitted and start hanging instead of completely releasing when deenergized. I tried to find an electrical drawing/schematic for the R4514 and couldn't find one to verify a solenoid(contactor)'s existence in this machine. Contact Ridgid service and ask if this saw has a contactor/solenoid in it. As stated earlier, the giveaway is where the manual states if power is lost, press the start button to start the machine again. If it was just a switch, that wouldn't be necessary.

[Bill Dufour]

Is there a transformer? I not you need a new switch. When it hums push the stop button and see if the noise stops.
Ridgid should be jumping to help. If you get an injury and claim the saw started by itself without a finger on the. start button they will lose in court after they have been notifie din writing of the problem.
Bill D

[Bill Howatt]

Hey Bill. Just looked at it again and it seems the hum is from the switch. But cannot be absolutely sure as sometimes the hum is loud and sometimes softer.

If you the manual, does it mention anything about a soft-start? I saw a soft-start reference somewhere when I was searching for a manual. If it does, it could be the humming is coming from that circuit. Does it continually hum or does it stop after a little while? Some inverter drives do keep running a while before they go into a complete idle. I hope you realize I'm just speculating on possible causes. You really need Ridgid to confirm your observations.
Did you try giving it a few good whacks to see if the replacement fixed that issue?