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?

"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

On Sat 10 Apr 2004 04:18:05p, "Bernard Randall"
wrote in
:

They're giving you a LOS, it's 99.999% certain that it is being driven
by a single phase induction motor.

Well, now it's 100% certain. That's the spec. :-)

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,

The stated motor speed is 3450, yes.

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%.

That would explain why they're taking their time getting back to me. :-)
I thought it sounded funny.

So, the performance package I ordered from In-Line with the machined
pulleys which will bring the saw speed down to 3830 won't *really* slow
the blade even more than that. I wasn't all that worried about it, but
I'm glad I asked

Thanks, Bernard.