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My second table saw was an inherited 8" saw with an aluminum table that I think came from Montgomery Ward. It was a contractor style saw with a 1 hp 3450 rpm induction motor hanging on the back of it. It was a terribly poor quality saw that required checking the wind direction and speed, the levelness of the saw, and to see if any ghosts were in the area before making a cut, but even then, no two cut pieces cut came out straight or the same width. As soon as I could afford a better saw, this one went to the scrap yard.

One day while I had it I got the bright idea to put an electrical brake on it to stop the motor from coasting when I shut it off. Being an EE I knew what needed to be done to make an electrical brake for it. I installed a three position switch with Off being the center position. One way ran the motor normally and the opposite way was spring return to the center off position. On this spring return side of the switch I installed a diode rectifier circuit that applied 150 VDC to the motor whenever I pushed the switch to that position. A brief DC power pulse on an induction motor will stop the motor from spinning very quickly, and not damage the motor.

Well, the first time that I activated this brake, the saw did indeed stop the motor very quickly, probably in less than a revolution, but then there was a rattling sound. The quick stop had unscrewed the blade nut several turns and the blade was spinning free on the shaft. Not spinning fast, but still turning and wobbling.

Once I figured out what had happened, I put a low value, high wattage resistor in series with the diode circuit, so the brake wouldn't be quite as effective, but I still had to make certain that the arbor nut was good and tight whenever I changed the blade, or this would happen again.

I haven't bothered to try this on any of the saws that I've owned since this one, because about the same time I built a dedicated shop and could lock it and the power to it to keep my kids out and away from my tools, so having a saw brake became less important to me.

So the moral of my story -

Having the arbor and nut threaded correctly for the right or left tilt design of the saw is very necessary and helps keep the arbor nut tight against the blade, but only if you don't try to stop the motor too quickly. If you install the incorrect arbor for the kind of saw, you will have the same problem that I did with my brake. If it's wrong, every time you try to cut a board and put a load on the blade the arbor nut will loosen and the blade will stop spinning.

Charley
 
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