I have a 1970s Rockwell lathe that has a AC-motor belt-drive. There are
four speeds. Any idea on how to determine the RPM?

Mike

well, here is what you do.
1. put the belt on one set of sheaves. rotate the motor by hand and count
how many turns of the motor equals one turn of the spindle. Write that
down. Repeat for each of the other three belt positions.

2. locate the nameplate on the motor and read out the RPM - if it's not
listed,or you can't find the nameplate, assume that it's 1750.

3. multiply each number you wrote down in step one by the motor speed you
located in step 2. Write those down.

4. print up a nice fancy lathe speed table using the numbers in step 3 and
put it next to your lathe.


"Lauritzen" wrote in message
news:4bzrc.8354$g71.4130@clgrps13...
I have a 1970s Rockwell lathe that has a AC-motor belt-drive. There are
four speeds. Any idea on how to determine the RPM?

Mike

Or: Measure your pulley sizes - outside OK, since you're interested in a
ratio. If the Pulley on the motor is 4", lathe 2", the ratio is 2:1.
Multiply by the motor speed.

If I were a betting man, I'd say minimum is 600.

"william_b_noble" wrote in message
s.com...
well, here is what you do.
1. put the belt on one set of sheaves. rotate the motor by hand and count
how many turns of the motor equals one turn of the spindle. Write that
down. Repeat for each of the other three belt positions.

2. locate the nameplate on the motor and read out the RPM - if it's not
listed,or you can't find the nameplate, assume that it's 1750.

3. multiply each number you wrote down in step one by the motor speed you
located in step 2. Write those down.

4. print up a nice fancy lathe speed table using the numbers in step 3 and
put it next to your lathe.


"Lauritzen" wrote in message
news:4bzrc.8354$g71.4130@clgrps13...
I have a 1970s Rockwell lathe that has a AC-motor belt-drive. There are
four speeds. Any idea on how to determine the RPM?

Mike

To find a minimum speed the smallest pulley would be on the motor.
With a 4" pulley on the headstock and a 2" pulley on the motor the ratio is 2:1
A normal motor of 1725 divided by 2 would be approx 862.5.
Your theorie suggests a high speed setting with the large pulley on the motor.

Or: Measure your pulley sizes - outside OK, since you're interested in a
ratio. If the Pulley on the motor is 4", lathe 2", the ratio is 2:1.
Multiply by the motor speed.

If I were a betting man, I'd say minimum is 600.


Bob, Naugatuck Ct.
http://www.outofcontrol-woodturning.com

Uh, not really. Read it again. Guess I threw you with my "reality" point.

I use it with kids in class because they learn math with calculators, and if
they plug the wrong value in, they get trash - unless they have an estimate
of valid range or "reality" point.

Motor speed times ratio of motor to spindle pulley (diameter,
circumference, no matter) equals spindle speed.

Thus if 1.5 on motor and 4.5 on spindle - 1/3 times 1725 = 575 - pretty
common.

"Bob Pritchard" wrote in message
...
To find a minimum speed the smallest pulley would be on the motor.
With a 4" pulley on the headstock and a 2" pulley on the motor the ratio
is 2:1
A normal motor of 1725 divided by 2 would be approx 862.5.
Your theorie suggests a high speed setting with the large pulley on the
motor.

Or: Measure your pulley sizes - outside OK, since you're interested in a
ratio. If the Pulley on the motor is 4", lathe 2", the ratio is 2:1.
Multiply by the motor speed.

If I were a betting man, I'd say minimum is 600.


Bob, Naugatuck Ct.
http://www.outofcontrol-woodturning.com

George wrote:
Uh, not really. Read it again. Guess I threw you with my "reality" point.

I use it with kids in class because they learn math with calculators, and if
they plug the wrong value in, they get trash - unless they have an estimate
of valid range or "reality" point.

Motor speed times ratio of motor to spindle pulley (diameter,
circumference, no matter) equals spindle speed.

Thus if 1.5 on motor and 4.5 on spindle - 1/3 times 1725 = 575 - pretty
common.

"Bob Pritchard" wrote in message
...

To find a minimum speed the smallest pulley would be on the motor.
With a 4" pulley on the headstock and a 2" pulley on the motor the ratio

is 2:1

A normal motor of 1725 divided by 2 would be approx 862.5.
Your theorie suggests a high speed setting with the large pulley on the

motor.

Or: Measure your pulley sizes - outside OK, since you're interested in a
ratio. If the Pulley on the motor is 4", lathe 2", the ratio is 2:1.
Multiply by the motor speed.

If I were a betting man, I'd say minimum is 600.

Your guess is probably accurate, and the math fine, but they're counter to each
other. A 2/1 ratio on a 1750 motor would be a speed of 3500; a 1/2 ratio (2"
motor pulley, 4" headstock) would halve the speed. If the kids don't think
through the problem to arrive at a reasonable reality point, what they expect to
get and what they get will be way off and probably stump them for a while until
they do think it through.

In other words, your reality point was for the low end, and the example for the
high end. That tends to throw folks...

....Kevin
--
Kevin & Theresa Miller
Juneau, Alaska
http://www.alaska.net/~atftb

I used a new paragraph and everything!

Sometimes there's just no perfect way to way to do things.

"Kevin & Theresa Miller" wrote in message
...
George wrote:
Uh, not really. Read it again. Guess I threw you with my "reality"
point.

I use it with kids in class because they learn math with calculators,
and if
they plug the wrong value in, they get trash - unless they have an
estimate
of valid range or "reality" point.

Motor speed times ratio of motor to spindle pulley (diameter,
circumference, no matter) equals spindle speed.

Thus if 1.5 on motor and 4.5 on spindle - 1/3 times 1725 = 575 -
pretty
common.

"Bob Pritchard" wrote in message
...

To find a minimum speed the smallest pulley would be on the motor.
With a 4" pulley on the headstock and a 2" pulley on the motor the ratio

is 2:1

A normal motor of 1725 divided by 2 would be approx 862.5.
Your theorie suggests a high speed setting with the large pulley on the

motor.

Or: Measure your pulley sizes - outside OK, since you're interested in
a
ratio. If the Pulley on the motor is 4", lathe 2", the ratio is 2:1.
Multiply by the motor speed.

If I were a betting man, I'd say minimum is 600.

Your guess is probably accurate, and the math fine, but they're counter to
each
other. A 2/1 ratio on a 1750 motor would be a speed of 3500; a 1/2 ratio
(2"
motor pulley, 4" headstock) would halve the speed. If the kids don't
think
through the problem to arrive at a reasonable reality point, what they
expect to
get and what they get will be way off and probably stump them for a while
until
they do think it through.

In other words, your reality point was for the low end, and the example
for the
high end. That tends to throw folks...

...Kevin
--
Kevin & Theresa Miller
Juneau, Alaska
http://www.alaska.net/~atftb