How to determine lathe speed

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.

1. 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.

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

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

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.

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.

Bob, Naugatuck Ct.

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.

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

I used a new paragraph and everything!

Sometimes there's just no perfect way to way to do th> > Uh, not really. Read it again. Guess I threw you with my "reality" point. > >