TS Pulley Size Science

[glenn bradley]

I have a Contractor-style TS with a 3450 rpm motor and a 2.5" pulley on motor shaft and arbor shaft. That's easy math. My other TS uses a 1780 rpm motor with a 4" pulley on the motor and a 2" pulley on the arbor. What gives? The reason for the question is I plan to upgrade the stock pulleys to balanced machine pulleys on the TS with dual 2.5" pulleys. I assume there is no need to alter the factory configuration but, everybody on SMC gives such great advice; I wanted to bouce it off you folks.

[Chuck Saunders]

Motor = Blade
3450*2.5*pi*= 3450*2.5*pi = belt speed inches/min
1780*4*pi = ?*2*pi = belt speed inches/min
since the belt speed is the same the Blade is turning twice as fast
2*1780 = 3560rpm
Chuck

[glenn bradley]

Thanks Chuck! See? I knew one of you guys would have some input. Thanks to everyone as usual!

[Jim DeLaney]

...My other TS uses a 1780 rpm motor with a 4" pulley on the motor and a 2" pulley on the arbor. What gives?...

Glenn,
Nearly every (new) TS I've seen has used a 3450 rpm motor. Has yours perhaps had a motor replacement?

What about horsepower? Is the 1780 rpm motor of the same hp as the 3450 rpm one? Often (but not always) the lower rpm motors are fractional horsepower.

As for blade speed, Chuck has already given you the correct answer to that.

[Ken Garlock]

Say Jim, with a mechanical advantage of 1/2, won't the effective horsepower be 1/2 the motor rating?:confused:

[glenn bradley]

Jim, it was kind of an oddball question. The 3450 TS is a circa 1970's saw while the other is a 1940's saw which is not running a motor with the Craftsman or Emerson logo. I assume it's an alteration by my Grandfather. The motor is HUGE but labeled as 1 HP. Sidenote - it runs as smooth as glass.

[Kent Fitzgerald]

Say Jim, with a mechanical advantage of 1/2, won't the effective horsepower be 1/2 the motor rating?:confused:
Nope. HP = RPM * torque. When you use gearing to increase RPM, torque goes down, and vice versa. HP remains the same (except for frictional losses in the gearing).

[lou sansone]

Say Jim, with a mechanical advantage of 1/2, won't the effective horsepower be 1/2 the motor rating?:confused:

hi Ken
I think the answer is yes and no. the motor's hp and full load torque are fixed by design, but the torque at the pully will be 1/2 due to the 2:1 overdrive. The torque for a 1 hp motor @ 3600 rpm is 1/2 of the torque of a 1 hp motor designed to run @ 1750. When you overdrive the motor as glenn is planning on doing, you end up with the same net torque at the arbor that you would have had with the higher speed motor.

lou

[Ken Garlock]

OK gents. I see what I was overlooking. The torque is half but the speed is twice, so the net is the same work is done.

[Jim DeLaney]

OK gents. I see what I was overlooking. The torque is half but the speed is twice, so the net is the same work is done.


Yup, that's the way it works!

[Cliff Rohrabacher]

It is not a wash in terms of output when you change the pulley configuration.

Larger pulley on the motor raises the blade speed. However when done to an extreme you'll get a blindlly fast blade with no guts. You can stop the thing with almost every cut.

Reversing that so the motor gets the smaller pulley lowers blade speed but raises torque making it more of a slow but powerful bull dozer.


Bear in mind that merely spinning the blade faster will consume more energy all by itself.

[glenn bradley]

This was interesting:

http://www.maloneyenterprises.com/APDC.htm

[Ken Garlock]

It is not a wash in terms of output when you change the pulley configuration.

Larger pulley on the motor raises the blade speed. However when done to an extreme you'll get a blindlly fast blade with no guts. You can stop the thing with almost every cut.

Reversing that so the motor gets the smaller pulley lowers blade speed but raises torque making it more of a slow but powerful bull dozer.


Bear in mind that merely spinning the blade faster will consume more energy all by itself.

Now Cliff, you have to understand that these discussions tend to be academic and little things like air friction, belt and bearing friction are ignored. :eek: :D