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Old Delta Radial Arm Saw Motor Reset Button question

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  • Old Delta Radial Arm Saw Motor Reset Button question

    A while ago I acquired an old 12" radial arm saw and the motor reset button is taped down i.e. in a pressed state. If I remove the tape, it will not run. It actually has a flat washer between the tape and the button to assure sufficient pressure against tape stretch.

    In this condition it runs perfectly, quiet & does not overheat. Starts easily but does spin forever when turned off.

    Can anyone tell me what I should be testing & how? Also what are the risks of just running it this way until it quits for good? I rarely use it. I'm just in a fix all the stuff that needs fixing phase. (or at least that's what I am trying to do)

  • #2
    The reset button is there to open the circuit and turn off the motor if it overheats. Usually that will be due to jamming the blade, or other sustained overload. They don't actually open that fast.

    Yours, on the other hand, seems to have a problem, it won't reset.

    After it has operated, you have to push in the button to latch it in the operating state again. Yours apparently won't do that. Consequently yours was taped down.

    You can have a good look at it, and see if it appears to be somehow mechanically blocked, but most likely the problem is inside. Most of those are a bimetal disk that is domed one way when in the running position. It (or mechanically linked contacts) then makes contact with wire terminals and completes the motor power circuit. If it overheats, due to current, or due to a hot motor, or some combination of both, the disk "pops through" to be domed the other way as the bimetal expands, opening the circuit. When it cools, it won't go back by itself, and you need to "oilcan" it through by pushing the button.

    They may be broken, or otherwise screwed up so that they don't make reliable contact. Can be as a result of mechanical abuse, operating too many times, internal arcing, etc, etc.

    While it isn't instant death to run without the protector, it does leave the motor open to overheating. The motor was made with it, got UL with it, and is better with it, unless you are careful not to overload it, which you can be without too much trouble, actually.

    I don't know if you can get replacements. Once upon a time, you could get them easily. Try a nice motor shop (not like the grumpy guy near me, who hates walk-in customers, and won't sell any parts).

    Keep eye on ball.
    Hashim Khan


    • #3
      Thanks, makes perfect sense
      I will open it up when I get time & try to fix/replace it


      • #4
        A friend of mine replaced the overheat switch on his a couple of years back, I do not know where he got the new one, but I know it was not cheap, I think he paid around $30 for it.
        Search the net for a parts manual for your model number saw. You should be able to find a new overload.


        • #5
          The overload switches are made by Klixon. Still available.


          • #6
            They make "switches".

            What is in question is whether they make THAT one.... It is, in most older motors, a largish "bakelite" device, that mounts in some way that the motor company decided they liked. Might be stone standard, or might be some crazy mounting the motor designer dreamed up. You need one that mounts like the one originally put in, and operates like it also.

            There were several companies that made them. The "Klixon" brand was one (maybe owned by TI at that time?), but there were others.

            Not only style of switch, but rating is of course important as well. Current, temperature, depends on how it works. May be a straight temp one , or a combo.

            Keep eye on ball.
            Hashim Khan


            • #7
              Okay It's actually a Dewalt model 790 12" Contractor Saw

              Pulled it out & removed the cover plate, I had forgotten it was dual voltage.
              Hmm built in brake...wonder how to fix that?

              So problem found...the sucker is cracked clean thru.


              • #8
                So it's a Model 7790/3431 Type 6
                I found an Instruction Manual but no parts diagram for this model. Did find for Type 8, looks similar, but the overload protector is not available.


                Anyone know if removing the old one would provide replacement information like a manufacturers part#?
                Really don't want to spend a bunch of money on this right now

                I do have a the ability to make a new mount for a replacement the will fit in the space.

                Edit: Based on a quick look, it sure looks like a Klixon phenolic

                Need to stand on my head and study the old one in place more.
                Last edited by BigSpike; 09-24-2014, 01:26 AM.


                • #9
                  The manual for that machine is here:

                  The reset switch is a simple thermal circuit breaker. It would be worth removing it to see if it is salvageable. The switch in in series with the motor so it has to carry 20A for a 120VAC circuit.


                  • #10
                    I wish I knew the company name that my dad found to have replacements parts for these saws. If I can find it in the mess that is around the saw, I will let you know. May take my a bit of searching to find the info. Dad has been gone since '95 and he discovered the info several years before.

                    Mentally confused and prone to wandering!


                    • #11
                      I must have had a brain cramp the other night, no need to stand on my head...just flip the motor over DUH
                      So after I did that, I could read the number on the overload protector

                      which matches up to the codes used by Klixon
                      found a datasheet
                      that shows this to be
                      C=1" dia.
                      E=eared commercial
                      J = 3 solder high cap
                      D=Disc & Contact 1" High Cap
                      B=120° degree

                      Also found a distributor that stocks this part
                      cost with shipping to me $36, well maybe next year,
                      I think I will pull out the old one & see if it can be glued back together