Calculate driven pulley RPM, belt speed, and find the right pulley sizes. Essential for setting up lathes, drill presses, bandsaws, and other shop machinery.
875 RPM is the output when a 3 inch motor pulley at 1,750 RPM drives a 6 inch pulley: a 2:1 reduction that doubles torque, moving the belt about 1,374 feet per minute. Bigger driven pulleys mean slower, stronger rotation. Use the calculator below for your exact numbers.
14" bandsaw with 1 HP motor. A step-pulley speed change system lets you dial in the right blade speed for any material.
View on Amazon Buy direct at GrizzlyDigital laser tachometer for verifying pulley RPM. Non-contact laser and contact tip modes. Essential for setup verification.
View on AmazonPremium V-belts for shop machinery. Heat and oil resistant construction outlasts standard belts 2:1 on lathes and drill presses.
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To increase speed, use a larger driver (motor) pulley or smaller driven (machine) pulley. To decrease speed, use a smaller driver pulley or larger driven pulley. The ratio of diameters determines the speed change.
For V-belts, maximum practical reduction is about 6:1, and maximum increase is about 1.5:1 in a single stage. Beyond these limits, belt slip becomes a problem. For higher ratios, use multiple belt stages or consider gear reduction.
Pulley size affects speed and torque, not power (which comes from the motor). When you reduce speed with pulleys, torque increases proportionally. A 2:1 reduction doubles torque at half the speed. Power remains constant minus friction losses. To choose the correct spindle speed for a given cutter and material, pair this with our feeds and speeds chart.
Belt speed is how fast the belt travels, measured in feet per minute. It's determined by pulley circumference times RPM. Belt speed affects heat buildup and wear. Most V-belts work best between 4,000-5,000 FPM and should not exceed 6,500 FPM.