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.515366

[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.


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[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?

[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.

[John Lanciani]

Maybe I missed it, has the OP actually confirmed what exact saw is in question other than to say "A Rigid jobsite saw"? If not, everything posted is idle speculation at best.

[Patty Hann]

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

Brian, can you elaborate on your suggestion?
Like an example of s rotary disconnect, where you have it mounted, etc.
Pics will help.
I have an older Dewalt jobsite saw (7480) that has the non magnetic paddle switch, but I'd still like to add some safety redundancy.
Also whatever you can explain and show pics of, I'm sure will help Diane.

[Brian Holcombe]

I usually build out an electrical box on every machine unless they already have one. I’ve attached a few examples, the brands I have used are Siemens and Eaton Moeller. They’re either round or they have a toggle that rotates.

I will typically also put e-stops in one or multiple locations on a machine depending on where I usually work from. If one were to have a situation in which you’re pulled into the feed of a machine it’s good to have immediate access to an e-stop so that you can increase your chance of survival.

While we’re on that subject, all three locations I commonly work in are stocked with a CAT tourniquet in addition to a basic first aide kit.

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515483515484515486

[Patty Hann]

I usually build out an electrical box on every machine unless they already have one. I’ve attached a few examples, the brands I have used are Siemens and Eaton Moeller. They’re either round or they have a toggle that rotates.

I will typically also put e-stops in one or multiple locations on a machine depending on where I usually work from. If one were to have a situation in which you’re pulled into the feed of a machine it’s good to have immediate access to an e-stop so that you can increase your chance of survival.

While we’re on that subject, all three locations I commonly work in are stocked with a CAT tourniquet in addition to a basic first aide kit.

515482
515483515484515486


Thank you much, Brian.
And totally off topic, but....what is the make/model (and age!) of that Drill Press?

[Brian Holcombe]

You’re welcome! That’s a modified auto tapping machine that I use as a drill press. The manufacturer is Kira (Japan), it was likely made in the 80’s but they still produce them.

I bought and modified it because I got a great deal on it and I love Japanese machines. It’s one of the heaviest and most precisely made presses of that stature that I have seen.

[Patty Hann]

You’re welcome! That’s a modified auto tapping machine that I use as a drill press. The manufacturer is Kira (Japan), it was likely made in the 80’s but they still produce them.

I bought and modified it because I got a great deal on it and I love Japanese machines. It’s one of the heaviest and most precisely made presses of that stature that I have seen.

Really, really nice. Thanks

[mike stenson]

very nice. I prefer the rotaries that allow for lockout/tagout, but that's a habit. Now I'm going to probably end up adding disconnects at my stationary tools. Thanks Brian for the reminder!

To me, this is like ensuring that a chamber is empty.

[Bill Dufour]

To meet code the school shop added a contactor to the work bench power supply. Used for small drills grinders etc. Turn on in the morning. turn off at the end of the day. If the power drops for a second or so it disconnects and all power tools are dead until the benches main power switch GO button is pressed.
Bill D.

[Mike Cutler]

Brian
Electrical devices aside, you have some nice work going on there!!
I don't know what you're making, but I'd really to see it when it's done. It looks exacting.

For the OP though.
If you have simple ON/OFF, magnetic switch, it should not be humming.
My shaper hums when not in use because there is an interposing relay and contractor in the power box. Delta made their shapers to run on 3 phase power, and that same box is on all of the machines of my vintage, even though, I have two pole, single phase 240 going to it only.

[Brian Holcombe]

Thanks, Mike!

[Diane Barker]

Hello All, just an update. Ridgid did get back to me and asked me to destroy the saw and they are sending me a new saw. I have to say, it was the right thing to do....but I am still impressed, considering how many companies do not back their products these days.

[Bill Howatt]

That is impressive these days and also a good solution rather than the try this part, try that part method. Glad you had a decent and safe(!) outcome for the problem.

[Mark Hennebury]

Good for you!

[David Dille]

Good for you. I go one step further and unplug. Controlling hazardous energy means to physically incapacitate the tool. I.E. a crush proof block under a hydraulic press after removing the tool from its power source. That’s why we stick a block under a jacked up car. If the Jack fails, the block will physically stop the car from crushing you. I wish more people would take these precautions.

I definitely wouldn’t use the saw until the issue was figured out and solidly fixed.

[Doug Garson]

Good that they are willing to replace the defective machine, not so good that they don't want you to return the saw at their expense so they can figure out what went wrong and prevent it from happening again.

[Patty Hann]

Good that they are willing to replace the defective machine, not so good that they don't want you to return the saw at their expense so they can figure out what went wrong and prevent it from happening again.
Yep. That is sad. Maybe Ridgid is waiting for a lawsuit (or three) before they will do anything constructive to eliminate the problem.
Not unlike Ford deciding that it was cheaper to pay out for wrongful death lawsuits than to redesign the Pinto's "exploding gas tank".

[Ken Combs]

Good that they are willing to replace the defective machine, not so good that they don't want you to return the saw at their expense so they can figure out what went wrong and prevent it from happening again.

I'd bet they know what it is and have either seen it before with another customer or duplicated it in testing.