when the saw's motor gets sluggish

[Bob Hammond]

Hi, it's been tough sledding this summer. At the end of May my basement shop was flooded, and it's taking time to get it sorted out, in part because I busted my wrist when I flew over the handlebars of my bicycle. So I've been working in the garage, and using a 1959 DeWalt radial saw for most operations (a capable machine when used with considered forethought).

So I was ripping short and thin pieces, >and I >>never ever reach around behind any running circular saw blade<< for any reason because that is very dangerous<, especially when cutting thin or short pieces. Since I was working with one wrist-hand in a cast I was especially cautious, and so I was cycling the motor on and off with every cut, and waiting for the sawblade to come to a full stop before extracting the workpiece.

After a 2 series of 5-8 cuts, the saw started to lag upon starting, and eventually just crawled and popped the circuit breaker. I let things cool down and tried again, but the same thing happened again. I called an experienced electrician-friend and discussed the problem, thinking that it was the starter capacitor. The tests were inconclusive, but I thought I'd just go buy a starter capacitor since it was the most likely part to be defective.

When I looked up the starter capacitor in the Grainger catalog, I noticed a specification for 'starts per hour', and it said 20 starts/hr. Well, a mystery was revealed. I was probably cycling the saw about every other minute when cutting the short/thin stock. So I tested the saw again, and cycled it with a duty cycle of ~30 secs. By the 5th start, the motor slowed on startup, and on the 6th attempt it wouldn't move.

So although the saw now starts okay (DeWalts have rugged motors!), I'm going to replace the starter capacitor (~$8 plus gas for travel), and then I'll be a bit more mindfull when I'm cycling it.

[David King]

I've seen that starts/hour cycle rating but it makes no sense to me and I've never experienced this problem. What part is heating up and causing this to happen? The start caps can't possibly care. They are rated way past their working voltage. Centripetal switch can't care unless arcing has welded the contacts shut which seems unlikely.

[Bob Hammond]

David, I don't know exactly. But I think that a specification for the starts/hour has a legitimate basis.

I've read some posts elsewhere about sniffing the capacitor(s) for a burnt odor. Maybe a rapid rate of charge & discharge cycles causes heating and then eventual breakdown of the dielectric materials inside a capacitor. As for a centripetal switch, it can't operate until the armature is rotating at the design speed, I would think.

Btw, when I bought the saw for $75 about 5-8 years ago, it looked pristine and still had the original table board on it from 1959, and it didn't appear to have been used much at all. But I did take the motor to a reputable repair shop and had it cleaned, examined, and the bearings replaced. When it runs, it runs sweetly quiet. The loudest sound is generated by the sawblade's teeth churning the air.