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206 Making Things Move

secure them. The term for this is plain bore. If the fit is too loose, you can always drill
and tap your own hole for a set screw. (See Chapter 3 for details on how to drill and
tap holes.)

If you’re not lucky enough to find a component with a convenient hub, you can always
press fit a component to your motor shaft. This is when the hole in your component is
so close to the size of your motor shaft that you need to push it really hard to slide it on,
and it will hold that position because of the stress of the fit. Figure 7-19 shows a gear
that ServoCity has designed to press onto the shaft of small DC motors.

CAUTION A press fit is one of the weaker methods we’ve talked about
for attaching components to a motor and is tricky to get just right. The act of
pressing on the gear or other component can also damage the radial
bearings in some motors because you are putting an axial load on the shaft
when you press something onto it. You should use this method only after
you’ve run out of other options.

Another way to attach components is by using a clamp hub, also called a flanged
coupling or mounting flange, like the one shown in Figure 7-20. This attachment
allows you to grip onto circular motor shafts with the clamp and then use the
mounting holes for gears, pulleys, wheels, or whatever you want. For larger diameter
motor shafts, McMaster sells a mounting flange (9684T1) that does the same job.

FIGURE 7-19 Press-on gear from FIGURE 7-20 Clamp-style hubs
ServoCity offer strength and flexibility.