Reversing Rotation of 115V Table Saw Motor

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Dean Huster
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Re: Reversing Rotation of 115V Table Saw Motor

Post by Dean Huster » Sat Aug 07, 2004 5:09 pm

Toejam, that's a mighty fine idea if you don't care when the family jewels get rapped up in the motor pulley/belt. Most belt-driven contractors' table saws have the motor hanging on the outfeed end of the table.<p>Also, finding an arbor nut is a buy directly from the saw manufacturer. And those nuts aren't designed for jamming. And those aren't Unified threads on that arbor, either. Most arbors are short enough that you wouldn't be able to use a dado head or a shaper head with such a modification. And any modification like that to jerry rig a saw into some kind of use is extraordinarily dangerous. Anyone who gets the idea that this might be a fix is to be warned away from any such foolishness.<p>Dean
Dean Huster, Electronics Curmudgeon
Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).

R.I.P.

Ed B.
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Re: Reversing Rotation of 115V Table Saw Motor

Post by Ed B. » Sat Aug 07, 2004 8:03 pm

Hey you guys -
If a capacitor shifts the phase of the starting winding to cause the motor to turn in a certain direction...How about replacing the capacitor with an inductor to shift the phase shift in the opposite direction ? The inductor will be cut out at a certain speed just like the capacitor would be ? ? ?
Ed B.

rshayes
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Re: Reversing Rotation of 115V Table Saw Motor

Post by rshayes » Sun Aug 08, 2004 12:15 am

You might look at the old motor to find out why it is defective. You have nothing to loose, since it is presently useless and not under warrenty.<p>There is a fair chance that the running windings are undamaged. These will have the heaviest wire in the motor, and copper isn't all that easy to melt. A short within a winding is a possibility that is hard to check, but will probably cause the motor to draw obviously excessive current.<p>A bad motor winding will mean rewinding the motor, which may be more trouble than it is worth. Broken leads or connections to the windings should be easy to repair.<p>The weak area is the starting winding. It may be of smaller wire than the running winding. However, the winding is only one of three parts in the starting circuit.<p>The starting circuit will have a starting capacitor, a centrifigal switch, and the starting winding in series. Both the capacitor and the switch are parts that are reliability problems in any electronic system.<p>The capacitor is probably an electrolytic unit. They have a finite life in the five to ten year region just sitting on the shelf. If the seals aren't perfect, they dry out. If overheated, they release a little water as vapor through a pressure seal and dry out faster. Life can also be shortened by heavy use. Then there are the early failures that tend to occur anyway (infant mortality). If the capacitor opens or shorts, the motor will not start.<p>The centrifigal switch probably has mechanical contacts in it. These are another reliability problem. The contacts themselves can be heavily pitted or have oxide deposits that will keep the switch from closing. In a centrifigal switch, these will probably be held closed by small springs, which may be damaged or missing. A little bit of rust in the right place may mean that the springs can't close the contacts.<p>It doesn't hurt to take apart a failed part. You can usally learn something from it. Like the $30 automotive relay assemblies that fail because of a transistor that can be easily replaced for 25 cents. I wonder how many $1000 engine control computers are junked for similar reasons.

toejam
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Re: Reversing Rotation of 115V Table Saw Motor

Post by toejam » Sun Aug 08, 2004 4:48 am

Dean:
Anyone who uses a 1 hp saw and has replaced the motor in it should be aware of the danger presented by the use of it, as well as that of rotating belts and pulleys. My saw uses standard nuts for the arbor as well as every other saw i have used. Sometimes you need something to work so you can find the time to fix it.

Lin Farquhar
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Re: Reversing Rotation of 115V Table Saw Motor

Post by Lin Farquhar » Wed Aug 11, 2004 7:01 am

Along the lines of Ed B's suggestion, take a look at
http://www.homemetalshopclub.org/news/sep01/sep01.html
Rgds, Lin

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