Teeth that work together

By How things are built · myAudience

myAudience · AI-generated original illustration · Original AI-generated illustration; not documentary evidence; no third-party artwork reproduced.

Meshing gears transfer rotation through contacting teeth. For two compatible external gears, a turn of the first advances teeth on the second, which rotates in the opposite direction. Tooth spacing and shape must match; two circular objects that look attractive together do not automatically form a working mechanism.

The number of teeth determines the ideal rotation ratio. A driver with 20 teeth turning once advances 20 teeth of a driven gear with 60 teeth, so the driven gear turns one third of a revolution. The driven angular speed is one third of the driver’s under those assumptions.

An ideal speed reduction can increase output torque while conserving mechanical power. Real mechanisms lose energy through friction and other effects, so actual performance is less than the ideal relationship. Torque is a turning effect and should not be confused with angular speed; increasing one can come at the expense of the other.

Worked example: a 20-tooth driver rotates at 120 revolutions per minute and meshes with a 60-tooth driven gear. The driven speed is 120 × 20/60 = 40 rpm, in the opposite direction. Check: does adding a simple intermediate gear between those two change the overall tooth-count speed ratio? It changes the sequence of directions, while the endpoint ratio remains set by the driver and final driven gear in this simple arrangement.

The generated gears are a still-life illustration, not verified tooth geometry or a fabrication plan. These calculations assume compatible, rigid gears with no slipping or compound arrangement. A real design also needs suitable bearings, materials, clearances, lubrication and protection from pinch points.

Image: illustration, not a documentary photograph.