Worm Gear

I have a question that is somewhat irrelevant to VeX. How do you calculate the gear ratio on a worm gear?

Check out:


bottom of the page…

BTW…I believe the math works out to 24:1 (can someone validate my math?)

thanks! and ya it is 24:1.

The arithmetic is easy… One turn of a worm screw will move a worm wheel an angular distance of one tooth.

The Vex worm wheel has 24 teeth, so 24 rotations of the Vex screw cause 1 full rotation of the Vex worm wheel.


So, with a worm gear you basically always get 1/x of the speed but x torque?

This is true with the Vex worm gear, because it is a “single start” worm gear. This means it has one tooth spiraling around it. If you look at the end, you will see only one tooth “starting” (single start).

There are worm gears that have two or more spiral teeth, and those worm gears will provide n/x of speed, but x/n of torque (where n is the number of spiral teeth on the worm gear, and x is the number of teeth on the worm wheel).

So, a “two-start” worm gear will have two spiral teeth (which can easily be counted by looking at the end of the worm gear). This worm will provide 2/x speed, and x/2 of torque.


  • Dean

I inserted “Vex” into the first sentence of my earlier message to be more precise about it applying specifically to the Vex equipment, and not to every possible worm screw/wheel design.