Page 217 - Making things move_ DIY mechanisms for inventors, hobbyists, and artists

Chapter 7 Bearings, Couplers, Gears, Screws, and Springs 195

example of a bearing installation where the
FIGURE 7-6 Bearings in inline skates
outer race will be held stationary while the mounted so inner races are clamped while
inner race spins with the threaded rod. outer races are free to spin

You can also install a bearing so the inner
race stays still and the outer race moves.
This is how inline skates and skateboard
wheels are mounted. The inner races are
squished together, while the outer races fit
snugly into a plastic wheel, so the wheel
and outer race of the bearing rotate
together (see Figure 7-6).

Radial Bushings
Radial bushings are a better choice for low
speeds, light loads, or when precision
frictionless movement just isn’t necessary
(or in your budget). A radial bushing looks
just like a section of a small pipe or straw.
These bushings usually come in a variety of
plastics, bronze, and sometimes aluminum
or steel with a low-friction coating on the
inside like Teflon or Frelon. Oilite bushings
are a special kind of bronze construction
that allows many tiny open pores to be
filled with oil and create a very slick surface.

NOTE Teflon is DuPont’s brand name for a slippery plastic with the
molecular name of polytetraflourethylene, abbreviated PTFE. So if you see a
PTFE on McMaster, it’s the same thing as Teflon.

Three measurements that define radial bushings are outer diameter, inner diameter, and
length. Before installing a bushing, make sure it fits on your chosen shaft and spins
without being too tight or too loose. To install a bushing, just press or hammer it into a
hole the size of its outer diameter. If you have access to an arbor press (like McMaster’s
2444A61), that’s even better. Using some kind of lubricant (like WD-40, 3-IN-ONE, or
certain greases) is always a good idea and will decrease friction even more.