Motor speed ?

[Jack Clay]

I have a 1750 3 hp motor that is not a (RI motor). If I configure the pulleys to get the same arbor speed as a 3450 3 hp motor will I see any performance different at the blade? I thought there must be something different since they changed to 3450 on every table saw I see. Thank you for your help.

[Tom Veatch]

There may be small overall efficiency differences, but, except for that, if you have room to install pulleys with the right pitch diameters, you should see the same torque and RPM at the blade in either case.

[Tom Esh]

Generally there's no difference. However at higher torque a small pulley may slip more easily just because there's less contact or grip area with the belt.

[Chip Lindley]

(IMO) you will NEVER gain anything by changing to a slower motor. It is only better than nothing if that is all available. All other things being equal, doubling the size of the motor pulley cuts the torque in half. The machine is running in a *higher gear*! Argueably, This is why larger hp motors are needed in high speed applications such as shapers.

Be aware that the belt may not have proper clearance when the blade is elevated or tilted, using a double-diameter motor pulley.

Old Delta/Milwaukee Unisaws used a 1725 rpm motor. But, those were induction/repulsion motors which had a very high torque to be rated @ 1hp! I owned an old Rockwell 6" jointer with a factory 3/4hp, 1725 rpm motor. It performed just fine.

[Jack Clay]

That’s were I get confused because the formulas I fond shows that the torque will double at the 1750 motor. If this is correct this would put the blade at the same torque level. Math headache.

[Dick Strauss]

(Torque x Speed(rpms))/5252 = HP...so using any given hp motor, if pulleys give you double the speed, you'll end up with half the torque at the same hp. Assuming you can get the pulleys to work out, you will lose some hp to the pulleys and belts but IMHO it isn't significant. You probably won't notice a difference.

[Mike Henderson]

That’s were I get confused because the formulas I fond shows that the torque will double at the 1750 motor. If this is correct this would put the blade at the same torque level. Math headache.
No, you're correct. HP is essentially torque times RPM so when you cut the speed in half, you double the torque. That's why four pole (1724RPM in the US) motors are physically larger than two pole motors for the same HP.

And RI motors do not have more torque at full speed. They do have more torque at startup (compared to a capacitor start motor). But when operating within their normal operating speed range, the torque is exactly the same as a capacitor start motor (for the same HP rating).

Mike

[Harry Niemann]

This all goes back to the basic " you never get anything for nothing" Double the speed , halve the torque, Halve the speed double the torque.