So, I heard a strange noise in the shop tonight...

[Monty]

.... and I went down to find that my table saw was running. 8-O This does not make me happy. It had been running for a while, too -- I could smell the rubber from the belt and it felt hot (I had a dado stack still on the arbor from the last time I used it).

I tried pushing the red "off" button and it didn't work. I had to unplug it to get it to stop, and then when I plugged it back in it started running again. This made me even less happy, since magnetic switches are definitely NOT supposed to do that! Out of nothing more than frustration I gave the switch a good WHACK, and then it worked as normal.

Needless to say the poltergeist will remain unplugged until I sort this out... any idea what the problem is?

 

[erasmussen]

Contacts welded shut on the switch
Mag switches are noemaly just 1 no 1 nc pushbutton switches and a big contactor (relay)

 

[junquecol]

If your saw is a Delta, do a search over on Woodnet.net as this problem has been the topic of several threads in the last year.

 

[MarkW]

I don't think it would be welded contacts since banging the box broke it loose. I'd suspect the spring that holds the contacts out broke or somehow came loose. I cannot think of anything else that would caused it. I obviously have not seen your particular magnetic starter or switch, but I have seen some that lost the spring and you could basically tap it to start or stop depending on how the contactor or switch was situated.

Good luck with it.

 

[Monty]

Thanks for the ideas - I found this thread on Woodnet, which was just like my situation, but nobody had an answer about why it happened. I also followed the link to this page about magnetic switches -- very interesting (scary) reading. However, I'm sure that nothing hit my saw.

I took the cover off the switch just to make sure there was no dust in there, and I don't see a single speck of dust in there.


:eusa_thin :-?

 

[Monty]

By the way, I neglected to mention my saw is a Jet:

 

[ChrisMathes]

Time for a new saw...after all that is, what 4-5 mos old now??? Yikes...I hope you get to the bottom of that fast, especially with the small village of kids you have living there...hehe. Good Luck!
Chris

 

[toolferone]

I show my customers all the time how I can hit my switch and have it turn on. Probably a good reason to retract the blade when not using it and to unplug the saw when changing blades.

 

[Monty]

Time for a new saw...

Hey, great idea!!! I was just thinking of just replacing the switch, but maybe I'm thinking on too small a scale! :icon_thum Now let's see, there's the SawStop™.... I wonder if they make a SawDon'tStart?!?!? :lol:

 

[Alan in Little Washington]

I think all these problems came about a few years back when all the tool manufacturers switched magnetic starters. They changed their tools with magnetic starters from LVC (low voltage control) with separate heavy duty (US made) contactors, transformers, and over-current cut-out switches (heater), all in a separate enclosure from the momentary contact start/stop buttons; to self contained magnetic switch boxes (likely made overseas). I think Grizzly was the first- they all look alike. When I look at the contactors in my old style LVC boxes, I can't see any way other than extremely severe bashing (that would also break the other components as well as the spring) that it could self start. I'm surprised, though, that the contactors aren't mounted so gravity would keep the contacts open if the spring had broken.

When ever we leave the house for a day or longer, I turn the shop power off.

 

[dtomasch]

Monty,
This is grave news for us fellow jet users. Please keep us informed as you do your research and I'll see what I can find. Don't want this happening at my house or anybody elses. Fire risk?

 

[Monty]

Thanks for the info... I have no idea what kind of switch this is. I can't see anything that looks broken or loose or out of place. I don't see anything that looks like a spring to me - maybe it's inside? If it helps, this is what my switch looks like: (click to see big pics if you want to read the stickers)

 

[michaelgarner]

there's the SawStop™.... I wonder if they make a SawDon'tStart?!?!? :lol:

You kill me!!! :rotflm: :rotflm: :rotflm:

 

[brent innc]

:lol: Maybe it was that little invisible man who runs around in there all the time. You know, the one who moves tape measures from their rightful place, puts the hammer in the wrong drawer, puts a screwdriver under the saw dust pile, the safety glasses in the house on top of your dresser, etc. You know the one I'm talking about. We all have that same litle man running around.:roll:

 

[woodguy1975]

Thanks for the info... I have no idea what kind of switch this is. I can't see anything that looks broken or loose or out of place. I don't see anything that looks like a spring to me - maybe it's inside? If it helps, this is what my switch looks like: (click to see big pics if you want to read the stickers)

The only way for the saw to start on it's own is for the spring of the contactor to be worn out so the coil made contact long enough for the coil to get energized and latch on. After that it probably go hot enough to somewhat weld the contacts in the on position requiring you to wack it to losten it up. Push the center part of the coil pack and see how the spring return works. Do this with the saw unplugged or you will start the saw. If the spring is wore you'll know it. The spring return should be strong.

For safety instead of unplugging the saw every time you could wire in a manual disconnect in line with your starter that you can throw when you aren't in the shop or even get a key switch. A simple disconnect like what is on your homefurnace or water heater would do the job.

Let me know if you want help looking at it. I've got just a little starter experience. If you want to go old school I have my old A/B starter from my jointer. LOL

 

[Mike Wilkins]

The switch on your machine looks like the generic magnetic switch that comes on a lot of machines from some Pacific rim location. You will find similar ones listed in various catalogs, such as Grizzly, Woodworkers Supply, etc. I have a similar switch on my refurbished Rockwell/Unisaw.
These switches sell for around $50 so I would stay on the safe side and find a replacement.
Woodworkers Supply is just down the street.
Good luck and watch those fingers.

 

[Monty]

I just got off the phone with WMH Toolgroup tech support. The guy told me that the switch assembly is supposed to "lock" in the housing box and shouldn't pull out like I showed in the pics above. Apparently there is a plastic or metal clip or spring that locks the switch assembly in place in the box. Well, mine wasn't locked, that's for sure. He thinks the whole switch assembly may have moved forward and contacted the pushbutton. I'll take a look tonight and see if I can tell what he's talking about.... stay tuned!

 

[cpowell]

Monty,

If the starter had shifted forward so the N.O. Start PB contacts were made it would seal in the run contact (just like it always does). Since the NC Stop PB contacts are wired in series with the coil, pushing the Stop PB should stop the saw so long as you hold the Stop PB down. If you pushed the Stop PB and nothing happened that is troubling. Not being able to start a machine is an inconvenience...not being able to stop it is scary.

By any chance when you tried to stop it did you simply push then release the Stop PB? If so then the motor would have restarted if the Start contacts were made.

There isn't enough current going through the coil to electrically "weld" control contacts but I agree they can get mechanically bound up. Starter contacts on the motor side do occasionally weld from high current.

Now I'm going to look at the starter on my Unisaw and see if it has the same susceptibility.

The whole problem could be avoided by having separate contacts on the Start and Stop PBs wired to the coil. Guess that would cost 50 cents more.

Be careful letting a gearhead M.E. (John) do Sparky work!! :lol: :lol:

Chuck

 

[cpowell]

I attached pics of my Unisaw starter (outside and inside) and the Mini-Max stop pushbutton.

The Start and Stop pushbuttons on the Uni have separate contacts, mounted to the right hand side of the starter. The buttons themselves are spring return as well as the contacts. The springs on these are quite strong. I don't think I am susceptible to a false start due to a spring failure. :eusa_thin

However, yours is the second post I've read recently where a machine started inadvertently while the owner was away. With that in mind, I may wire a toggle switch adjacent to the starter box and route control voltage through the switch. When not in use, I can flip the switch OFF and kill control voltage, rendering the starter inoperable. I would NOT change blades without pulling the plug though. Control voltage isolation is not acceptable for achieving zero energy state.

A better option would be to wire a mushroom stop switch like the one on my MiniMax. The stop button locks in the off position (pushed in) and must be twisted to return to a "ready" state.

If John is offering the AB starter that is a great option for reliability. The ones I've used are industrial grade and perform well.

Another option is a safety disconnect on the voltage mains but they are expensive (at least the ones I'm familiar with).

OK, I'm out of options (except for pulling the plug when you leave the shop or flipping the breaker).

Chuck

 

[Monty]

Thanks for the pics, Chuck. I just took a closer look at my switch. You can see the clip that holds the switch in place here (the switch is pulled out slightly):

You can see the little notch where the clip engages when you push it in (exact center of the pic). As the switch goes in the box, the ground wire in the back (at the top) can get caught behind the switch and prevent it from going all the way in. I can't say for sure whether this was a problem before I took the switch apart - I don't think it was. Even when the ground wire is held out of the way and the clip engages, I have to say it's far short of a "click". It does not feel securely locked in place, but it does take a little more force to pull out when the clip is engaged.

Right now the switch is reassembled (correctly) and working fine.... but I'm still keeping the saw unplugged. I think that replacing the switch will be the only thing that would make me fully comfortable with this thing again, but if I replace it with another cheap "pacific rim" style switch then I'm not sure I'll be gaining anything.

I really like the "mushroom' locking switch design like the MiniMax. My Shop Fox jointer has that, too. I know Powermatic jointers also use a switch like that. Anyone know where I can find one of these? I'm sure they're not cheap. I could just wire a toggle switch to kill the power. I have to admit I'm not sure what an A/B switch is, but hey - if it works...... :icon_thum For now, unplugging is free.