Page 164 - Robot Builder's Bonanza

SCREWS, NUTS, AND OTHER FASTENERS 133

Figure 13-5 Use a standard flat washer as a
Figure 13-4 Four common nuts for use with spacer or to spread out the surface area of the
machine screws: hex, acorn (or cap), threaded fastener. Split washers are used to help “lock” the
insert, and threaded coupler. fastener, preventing it from coming loose.

Figure 13-4 shows several popular types of nuts for machine screws— standard hex nut,
acorn (cap), nylon insert (locking), and threaded coupler. There are many more than those
shown here; I’ve limited the list to just those that are of most use in robotics construction.

• Standard hex nuts are the most common, so named because they have six sides (hexago-
nal = six sides).
• Acorn or cap nuts are like hex nuts, but with no hole on the other side. You can use them
for decorative purposes, but a more common application is as a balancing “skid” for a
two- wheeled robot.
• Nylon insert nuts have a nylon plastic core. They’re used to create self- locking mecha-
nisms. To use, tighten the nut into place. The plastic inside keeps the nut from working
loose.
• Threaded couplers are like very long nuts. Use them as spacers or, if very long, as “risers”
for the separate levels of your robot base.

For all, you may use a wrench or a nut driver to tighten.

WASHERS AND WHEN TO USE THEM

Washers are disc- shaped metal or plastic, used with fasteners. They aren’t fasteners them-
selves, but they augment the job of screws and nuts.
Washers come in two general forms: flat and locking (see Figure 13-5). Flat washers are
used as spacers and to spread out surface area. Each size screw has a corresponding
“standard- size” washer. Specialty washers are available with larger diameters and thicknesses.
For example, a fender (or mudguard) washer has a very large diameter in comparison to the
screw it’s used with.
Locking washers, or simply lock washers, come in two basic styles: tooth and split.
Tooth- style washers dig into the material and/or fastener to keep things in place; split lock
washers use compression to keep pressure against the fastener.

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