ab...@leftmind.net (AdB) writes:
> Similarly for most air tools; 30 seconds of zenlike contemplation of the
> next cut alternating with a 5-second cut can be an indication that
> you've got a lot of tool and not much compressor. BTDTGTT.
Bah, it turns out that a universal motor in a table saw is worse than
originally anticipated, in pretty much the same way.
I had decided that induction machines was simply a personal bias, and
there was no need to spend nearly a grand on a saw I wouldn't actually
use all that much. The one with the universal machine would be fine[1],
and was nicely discounted for the first quarter of the year (2008).
So I'm cutting a bunch of planks to the same length, got everything set
up and just have to chuck the wood through when A Strange Noise starts
coming from the motor assembly. Kill the power, and notice a bit of
burning belt smell.
Taking a good look at the inside of the saw, the true downside[2] of a
universal motor appears. Induction motors turn slower than the blade
speed, so they have a Big Pulley, and the blade gets a Little Pully so
you get the right saw speed. Universal motors, though, turn
faster--much faster in this case--than blade speed, so the motor gets a
Tiny Pully and the blade gets a Big Pulley.
Except, Tiny Pully really looked like it was just the motor shaft. So
the belt couldn't be a V-belt, it was just a thin, flat belt. And that
wasn't enough torque, so they had to put two on it. But still, they're
making an awfully sharp turn around the motor shaft...
...where they get really, really hot...
...and start to slip, making a horrible scary noise.
So, new procedure. Get board. Measure board. Saw on. Cut board. Saw
off. Put cut board aside. Repeat until done or the UPS starts asking
WTF is going on with all that surge and sag.
[1] As soon as I thought, "It will be fine," I should have known. Fine,
in my family, is a euphamism for "total piece of crap but it was
cheap and it will work if you force it". Made famous by the "fine
car" would couldn't make a sharp left turn, only lane change to the
left.
[2] I'd figured the badness would be commutator whine and resulting
noise. Well, no, a well-made universal motor is reasonably quiet
these days. It's a bit louder than an induction machine, but not
enough to justify an extra $600 for the saw.
--
"...and 8 inches is really not that impressive."
-- Kari Byron, Mythbuster