Gears and clock trains#

Real gears, not lookalikes#

The gear shape uses a true involute tooth: the curve that makes two gears turn at a steady ratio. A rounded tooth that just looks right will bind or jerk.

The root is cut the way a real hob would cut it. So small gears (few teeth) come out with thin, undercut roots, just as real ones do. That's correct, not a bug.

Module#

Module is tooth size. Two gears mesh only if they share a module.

pitch diameter = module × teeth

That's why you can't drag a gear bigger: changing its size would change its module.

Cycloidal gears and pinions#

Clocks often use cycloidal teeth with a lantern pinion (pins instead of teeth). The wheel's tooth shape comes from that pinion's pin circle, so they're made together as a pair.

Clock trains#

A clock is a chain of gears that turns the escape wheel's fast ticking into hands moving at the right speed. The designer works it out from the beat.

Why it must be exact#

Tooth counts are whole numbers. Not every beat can be hit exactly. When it can't, the panel shows red instead of rounding. 0.3 % fast loses about four minutes a day.

Why each mesh has its own module#

Force drops at each step along the train. The great wheel carries roughly sixty times the escape wheel's load. Same-size teeth everywhere would leave one end too weak and the other too coarse. So teeth get finer toward the escapement. Set Max wheel Ø and the designer sizes everything to fit.

Why each wheel is its own shape#

Once the train is set, you'll want to change bores, hubs and spokes per wheel. Each wheel is a normal shape you can edit. The clock chip reopens the designer without losing those changes.

How-to: Make a gear · Design a clock