gary's clocks

Fancy Gear Shapes-Just enough involute to matter

full fit involute gear set

Let's take a second look at the Involute tooth form.

This shows a pair of full fitting involute gears.

Gears found in machines or purchased from a catalogue would have tooth form like this.

The gears I used on my first clock design also had nasty gears like this.

(that'd be the ACAD plans you can download from this website)
  • very little backlash
  • three teeth engaged at all times
  • Lots of friction.

    Take advantage that clocks run clockwise

    Here is one of those things that should be obvious but isn't.

  • Clocks run clockwise.
  • They don't go backwards.
  • Ever!

    What this means to the clock maker is that

  • only one side of the gear tooth gets any wear.
  • Backlash or slop between the gear teeth is not a problem. This means we should design wooden gear teeth to have lots of backlash to compensate for wood movement (and compensate for the inevitable inaccuracies of our scrollsaw work)

    This animation shows how a standard involute gear can be modified to

  • reduce friction,
  • increase backlash
  • remain strong
  • and yet have the desirable involute face only where it matters.

    evolution gear

    Full view of the fancy gear.

    fancy gear 20

    The red line indicates the pitch circle diameter.
    The gears have the least amount of friction when the pitch diameters are in contact and little sliding is taking place.

    Let's take a look at this modified gear in action

    Is this cool or what?


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