"Dan" wrote in message
...
Okay, I've been running this around in my head and now I'm checking with
you folks.

In a previous thread I talked about dropping the speed on a Griz 1022. I
emailed Grizzly tech support asking if they could think of any problems
that might occur. I got a reply saying that the arbor speed of that model
was 4700 rpm but the blade speed was only 4140. They said it was "due to
the blade being installed".

I had a little trouble with that and asked them if they could explain it
in a little more detail. They replied saying they'd passed the question
on to the tech staff for research and someone will get back to me in a
timely manner. That was last Wednesday morning. As far I'm concerned,
"timely manner" has come and gone. I'm getting impatient, so I'm tossing
the question out to the wreck to see if anyone's got any thoughts.

The only reason for the drop in rpm that I can think of is because the
motor is turning slower. A drop of over 500 rpm at the arbor seemes a bit
much but after reviewing what I know about induction motors, I guess it's
logical to think rpm will decrease, though. The motor is trying to
maintain a constant energy output, not a constant speed, so speed would
be a function of load, and the extra mass of the blade is a load, so at
equilibrium, the motor rpm would be less than it would without the blade.
I think.

If putting a standard blade causes the rpm to drop by over 500 rpm, then
a dado set would cause even more of a drop, seems like.

So, is that woodworking-related enough? :-) Is there a rule of thumb
about blade mass, motor hp, and rpm drop?

They're giving you a LOS, it's 99.999% certain that it is being driven by a
single phase induction motor. The charactaristics of this type of motor,
lets assume for the moment it's a 2 pole motor, are that with no load it
will rotate at 3600 RPM, at full load the speed will drop to 3,450 RPM, if
the load increases much beyond its maximum rating the motor will stall. A 4
pole motor no load speed is 1800 RPM, its full load speed is 1725. Assuming
that it is not a direct drive, there is a belt and pulley system between the
motor and arbor, the size of the respective pulleys will determine the
resulting arbor speed. To save you calculating maximum speed change no load
to full load is less than 4.5%.

Bernard R