large or small pulleys?

[weston55]

I'm planning to build a drum sander (emphasis on planning for now) and need to know something about pulley sizes. The motor is 1725 rpm, the drum will be about 5.5-5.75" in circumference. I know that the pulley ratio needs to be about (motor) 7:8 (drum) for approximately 2,200 surface feet per minute. A 3.5" pulley on the motor with a 4" pulley on the drum will do it. If I halve the pulley sizes to 1.75" and 2" I get the same result. Is there any advantage to using larger pulleys if the ratio remains the same?

[Claw Hama]

Pulley speeds
D (large dia) x n (small revs) = N (large number of revs) x d (small dia)
Dxn = Nxd

Belt sizes
Pulley A dia x 3.142 div 2 plus
pulley B dia x 3.142 div 2 plus
distance centre to centre of pulleys x2 = belt size

[Skew ChiDAMN!!]

Is there any advantage to using larger pulleys if the ratio remains the same?

1. They give more surface area for the belt to grip, so will better handle variations in load. (ie. less likely to slip.)

2. If you go big enough, they can act as flywheels. This'd be irrelevant in the case of a drum-sander - unless you're using an extremely lightweight drum.

[Claw Hama]

Sorry Weston, got interuped mid thread and didn't read the whole issue. But Skews has the goods.

[weston55]

Thanks guys. Better grip on a larger pulley makes sense.

[joe greiner]

Yes, there is an advantage to using larger pulleys. Less flexing of the belt, so expect longer time to failure. Added to above remarks.

Cheers,
Joe

[Johncs]

Yes, there is an advantage to using larger pulleys. Less flexing of the belt, so expect longer time to failure. Added to above remarks.

Cheers,
Joe

Less flexing, less internal friction, less head generated in the belt. Take a look at pullies in the engine bay of your car, those last well.