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How to use it
Pulleys. With the pitch diameters, driving speed and centre distance you get ratio, driven speed, belt pitch length, wrap angle and belt speed. If you enter a commercial length, the tool recalculates the corresponding centre distance; with the power you get torques and tangential force.
Gears. With module and numbers of teeth you get pitch, tip and root diameters, centre distance, pitch and contact ratio; with the power, torques and forces on the tooth.
Formulas used
Beyond geometry
The geometry tells you whether the drive can be assembled; it doesn't tell you whether it holds up. The number and section of belts are chosen from the manufacturer's catalogue; gears need face width and tooth bending and pitting checks to ISO 6336, which depend on material, heat treatment and machining quality. We can handle the complete sizing of the drive as part of mechanical design.
FAQ
What's the minimum wrap angle?
For V-belts up to about 120° on the smaller pulley is considered acceptable, with a correction factor on the transmissible power. Below that there's a risk of slipping: increase the centre distance or split the ratio into two stages.
Why are at least 17 teeth needed?
With a 20° pressure angle and standard teeth, below 17 teeth the cutting tool removes material at the tooth root (undercut), weakening it. You can go down to about 14 accepting a slight undercut, or correct the teeth with a profile shift.
What's the maximum ratio per stage?
For belts it's normally up to 6–8, for a pair of spur gears about 6–7. Higher ratios are obtained with more stages or with planetary or worm gearboxes.
Does the module have to be standard?
It's advisable: modules from the ISO 54 preferred series (1; 1.25; 1.5; 2; 2.5; 3; 4…) have standard tools and cost less to produce and replace.