Need the formula to calculate what pulley size to use on what motor

Hi All,

Can someone give me the formula used to calculate what pulley size you need to fit to a motor to drive a small bench saw?

I picked up a very well build small steel bench saw, fitted with a 9" blade and it needs a motor.

I was thinking of using an old washing machine motor in the 1/2 to 3/4 hp range - depending what my local washing machine service centre has out the back:D

Details of the saw are -
Top plate is approx. 6mm steel. Pulley is 60mm diameter. Blade flanges are 75mm diameter. Body plate of saw bench is 2.5mm steel. Overall dimensions are 355mm(high)x500x560 mm.
Blade is 235mm diameter, has 30 teeth and is TCT (TUNGSTEN CARBIDE TIPPED). This is a good configuration for precision cutting. Blade bore is 25mm. Blade lift mechanism (see image) is very smooth but with no slop (as are all moving parts) and can be operated with one finger.


I will be using it to trim pen blanks, small boards for boxes and cutting samples down to size for my sample collection. The pulley on the blade drive shaft is 60mm in diameter and I need to know what size pulley I should put on the motor. See photos below of the unit.

Check the saw blade for a speed rating and run it at about 80% of that. If the blade is not speed labled (9 out 10 of my 235mm TCT weren't), I have a 235mm Irwin that has a max speed rating of 6500.The circ saw that it mounts to has an idle speed of 4300 RPM.

An induction motor will run at either 2880 or 1440 RPM approximately for 50HZ mains and about 20% faster for 60Hz. This is the brushless style of motor used on fixed machines like table saws, jointers, and drill presses . Some older washers used universal motors for spinning etc where high speeds were required. These motors run at higher speeds and the speed is model specific.

Targeting a blade speed of say 4000 to 4500 RPM, you would want a ratio of 3:1 for a 1440 motor or 1.5:1 for a 2880 motor. For a 60mm driven pulley, you would be looking toward a 180mm driver pulley for a 1440 motor or a 90mm driver for a 2880 motor. The 2880 motor is probably a better option as the ratio is closer to 1:1

Thanks for that Malb, I hate it when the maths gets complicated!

Regards

Brendan