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220 Making Things Move

FIGURE 7-32 Centering the circle within the gear

9. Now that you have your gears, you’ll create a base with holes spaced the
correct distance apart so you can mount the gears with 1/4 in wooden dowels
and make them spin.
a. Calculate the center distance (CD) of your gears using the equations from
Table 7-1. Both gears have a circular pitch of 24 pixels and a pressure angle
of 20°. The big gear has 28 teeth, and the small one has 14. As explained
in the project’s introduction, you convert the circular pitch in pixels to a
diametral pitch in inches of 11.781. If you look at Table 7-1, all you need is
that number and the numbers of teeth on the two meshing gears to find
the center distance (CD). Use the equation CD = (N + N )/2P, and you’ll
2
1
find that CD = 1.783.