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  #1  
Old 08-04-2014, 12:22 PM
Mölyapina's Avatar
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Had a scare with our radial saw -- ran away, white smoke. Any thoughts on a cause?

I was using our Craftsman radial saw today to cut up boards as part of my project of replacing the deck stairs. After cutting a board, I let go of the trigger and let the saw back up. Instead of stopping, it continued running. I reached over to jiggle the trigger in case it was stuck, but the saw continued running and started pouring out white smoke out of the motor. I then very quickly reached over to the power cord and unplugged it, at which point the madness ended. Any thoughts on what could have caused this?

EDIT: This is not a radial saw, it is a compound miter saw.
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1982 300SD -- 211k, Texas car, tranny issues ____ 1979 240D 4-speed 234k -- turbo and tuned IP, third world taxi hot rod

2 Samuel 12:13: "David said to Nathan, “I have sinned against the Lord.” And Nathan said to David, “The Lord also has put away your sin; you shall not die."

Last edited by Mölyapina; 08-04-2014 at 01:34 PM.
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  #2  
Old 08-04-2014, 12:46 PM
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OK, so I took it apart. The motor looked fine. The switch at the handle was stuck, so I unstuck it.

The switch helps answer why the motor didn't shut down, but it doesn't explain why it started pouring white smoke. Could that somehow be related to the switch? It is quite hot out -- could this be some sort of overheat? The motor seemed to running a bit slower than usual when it was out of control. Could this be a clue to the white smoke or just a result of the switch being half-open?
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"Senior Luna, your sense of humor is still loco... but we love it, anyway." -rickymay ____ "Your sense of humor is still loco... " -MBeige ____ "Señor Luna, your sense of humor is quite järjetön" -Delibes

1982 300SD -- 211k, Texas car, tranny issues ____ 1979 240D 4-speed 234k -- turbo and tuned IP, third world taxi hot rod

2 Samuel 12:13: "David said to Nathan, “I have sinned against the Lord.” And Nathan said to David, “The Lord also has put away your sin; you shall not die."
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  #3  
Old 08-04-2014, 01:15 PM
I miss my MBZ
 
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My most-likely hypothetical is this:
WHen the switch welded shut, it did so in a high-resistance manner (example: a bunch of current was being spent making heat in the switch so less was available downstream) dropping a lot of voltage through it and giving the motor lower-than normal voltage at the motor leads.
Lower than normal voltage on motors like yours (example: 80v on a 120v motor) will still run the motor, but it'll make less power, drop speed quicker and demand more current than normal (most 120VAC motors are 'tuned' to run efficiently at 120v, give them less and they act as described above).
Your low-voltage motor run circuit was so far off that the motor amps were up, high enough to heat the motor internals/insulation/metal plating and turn it to white smoke- which you saw.

Somewhere on the internet, are bottles of "magic smoke", normally with the manufacturer "Lucas", of British Sports car fame

Back in the real world - if you dont have a spare radial saw- I'd go ahead, power it back up (from a safe distance) it might work fine, it might not start, it might run slowly and smoke again. if it doesnt run well then the motor is probably permanently damaged, and you'll either need a new motor or a new saw. (if its a sears model- check searspartsdirect.com - they have a LOT of parts on there....) motors on these things are not difficult for a handyperson to replace.

Post up the manuf. and model number of the saw and maybe get more information from us

Lots of EE's on this board, I welcome corrections and feedback (I now work a lot farther from the power plant than I used to...)

-John
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  #4  
Old 08-04-2014, 01:19 PM
I miss my MBZ
 
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I'd also throw this out their for comment:
In my observations, there are 3 types of motor overloads in the consumer appliance world:
1) solder pot
2) circuit breaker
3) none (thermal failure of the motor windings, bearings or connections)

Both 1) and 2) will fully remove power from the motor until reset (if they work correctly). and shouldnt *normally* cause a 'slow run' condition.

Its easy to reset circuit breakers, solder pots are only reset by giving the motor 30+ seconds to cool down and then trying to restart it.

3) will just burn the motor until it fails completely. While this is isnt really overload protection, its cheaper and if the motor is really low HP, the risk of injury is relatively low.

In the old days, solder pots and circuit breakers would fail internally....giving you all kinds of mixed signals.


I'm interested to see what I'm missing here.
-John
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  #5  
Old 08-04-2014, 01:31 PM
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THanks for all that, John. Interesting stuff. The saw is a 10" Radial Compound, part #172.243600, with "2003 09-PO" next to it (I assume that this is a build date)?
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"Senior Luna, your sense of humor is still loco... but we love it, anyway." -rickymay ____ "Your sense of humor is still loco... " -MBeige ____ "Señor Luna, your sense of humor is quite järjetön" -Delibes

1982 300SD -- 211k, Texas car, tranny issues ____ 1979 240D 4-speed 234k -- turbo and tuned IP, third world taxi hot rod

2 Samuel 12:13: "David said to Nathan, “I have sinned against the Lord.” And Nathan said to David, “The Lord also has put away your sin; you shall not die."
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  #6  
Old 08-04-2014, 01:33 PM
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Correction: it is a compound miter saw. Need to get my tool names straight.
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"Senior Luna, your sense of humor is still loco... but we love it, anyway." -rickymay ____ "Your sense of humor is still loco... " -MBeige ____ "Señor Luna, your sense of humor is quite järjetön" -Delibes

1982 300SD -- 211k, Texas car, tranny issues ____ 1979 240D 4-speed 234k -- turbo and tuned IP, third world taxi hot rod

2 Samuel 12:13: "David said to Nathan, “I have sinned against the Lord.” And Nathan said to David, “The Lord also has put away your sin; you shall not die."
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  #7  
Old 08-04-2014, 01:35 PM
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I think it was those aliens again...

(glad you survived the attack)
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  #8  
Old 08-04-2014, 01:36 PM
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Agh! The switch is NLA! I wonder if it can be replaced with something else?
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"Senior Luna, your sense of humor is still loco... but we love it, anyway." -rickymay ____ "Your sense of humor is still loco... " -MBeige ____ "Señor Luna, your sense of humor is quite järjetön" -Delibes

1982 300SD -- 211k, Texas car, tranny issues ____ 1979 240D 4-speed 234k -- turbo and tuned IP, third world taxi hot rod

2 Samuel 12:13: "David said to Nathan, “I have sinned against the Lord.” And Nathan said to David, “The Lord also has put away your sin; you shall not die."
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  #9  
Old 08-04-2014, 01:41 PM
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Did you check eBay? Is the saw another brand with Sears just slapping their label on it?
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  #10  
Old 08-04-2014, 02:12 PM
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Part # on the switch is CB22-B. The manufacturer is Gaoyou Electrical Plastic Factory. I am continuing to find it as NLA. The website for the company itself is in chinese, so I can't read it.
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"Senior Luna, your sense of humor is still loco... but we love it, anyway." -rickymay ____ "Your sense of humor is still loco... " -MBeige ____ "Señor Luna, your sense of humor is quite järjetön" -Delibes

1982 300SD -- 211k, Texas car, tranny issues ____ 1979 240D 4-speed 234k -- turbo and tuned IP, third world taxi hot rod

2 Samuel 12:13: "David said to Nathan, “I have sinned against the Lord.” And Nathan said to David, “The Lord also has put away your sin; you shall not die."
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  #11  
Old 08-04-2014, 02:32 PM
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So my dad came home, and he was OK with me hooking the unstuck switch back to the machine, so I did. When I plugged it in, it instantly turned on, so I unplugged it. I tried to jiggle the switch to see if it was stuck and plugged it in again, and again it came on.

Then I had a idea. I plugged it in, it came on instantly... and then promptly switched off when I hit the trigger to turn it "on". So I guess that's just my genius wiring at work . It did seem to run fine (no smoke, etc.).
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"Senior Luna, your sense of humor is still loco... but we love it, anyway." -rickymay ____ "Your sense of humor is still loco... " -MBeige ____ "Señor Luna, your sense of humor is quite järjetön" -Delibes

1982 300SD -- 211k, Texas car, tranny issues ____ 1979 240D 4-speed 234k -- turbo and tuned IP, third world taxi hot rod

2 Samuel 12:13: "David said to Nathan, “I have sinned against the Lord.” And Nathan said to David, “The Lord also has put away your sin; you shall not die."
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  #12  
Old 08-04-2014, 03:00 PM
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Quote:
Originally Posted by Jooseppi Luna View Post
Agh! The switch is NLA! I wonder if it can be replaced with something else?
A common event in the power tool industry. I have a Rigid (Home Depot) 10" compound miter saw, but the bolt and washers that holds the blade on the spindle went missing when we moved. Went online to get replacements . . . the washers are available (and a new dust bag) but the $1.05 bolt is NLA. Luckily, it's not some weird thread design with internal moving parts, just a steel bolt that I got at the hardware store.
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  #13  
Old 08-04-2014, 03:49 PM
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None of my ideas would be deemed safe by anyone with a shred of common sense so I'll keep my swamp yankee hackery to myself for your own health and well being.

Good luck!
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  #14  
Old 08-04-2014, 06:40 PM
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White smoke . . . coolant in the exhaust . . . and there's a new Pope.
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  #15  
Old 08-04-2014, 08:44 PM
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Here's another, and very likely scenario. Most saws of this type have a dynamic brake which short circuits the motor when the switch is released to slow it down quickly. It is possible that the switch was in that position with the power still applied to the motor.
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