Page 163 - Robot Builder's Bonanza

132 ASSEMBLY TECHNIQUES

Pan Good general- purpose fastener. However, the head is fairly
shallow, so it provides less grip for the screwdriver.
Round Taller head protrudes more than pan head, so it provides
greater depth for the screwdriver. Good for higher- torque
applications when it doesn’t matter if the head sticks out.
Flat (or countersunk) Used when the head must be flush with the surface of the material.
Requires that you drill a countersunk hole (or if the material is
soft, like PVC plastic, drive the head down into the material).
Fillister Extra- deep head for very high torque. The top of the head is
rounded. Often used in model airplanes and cars for miniature
mechanical parts.
Hex bolt Doesn’t have a slot for a screwdriver, and requires a wrench to
tighten. For high- torque applications.

These are the most common, but there are at least a dozen others. They don’t see heavy
use in most robotics applications, so I won’t list them here.

SCREW DRIVE STYLES
Most screws available at the hardware store come made for different types of drivers (that is,
the tool you used to tighten or untighten the screw). For all types, different sizes of drivers are
used to accommodate small and large fasteners. In general, the larger the fastener, the larger
the driver.

Slotted Made for general fastening and low- torque drive; screwdriver
may slip from the slot.
Phillips Cross- point drive resists drive slippage, but the head is easily
stripped out when using an improperly sized driver.
Socket Hexagonal- shaped wrench resists slippage. Can be made very
small for ultra- miniature screws.
Hex Uses a wrench or nut driver to tighten or untighten. Nut drivers
look like screwdrivers, but with a hex socket at the end. You can
use these tools to tighten nuts, too.

Which to use? I personally prefer Phillips. They’re particularly well behaved when using
motorized screwdrivers. Downside: The head of a Phillips screw can be greatly mangled by
using a too- small or too- large screwdriver bit, so choose your tools carefully.

GOING NUTS OVER NUTS
When using machine screws you need something to tighten the screw against. That’s the job
of the machine screw nut. (You can also use tapped threads in the material itself; that’s covered
later in this chapter.) Nuts must be of the same size and thread pitch as the machine screw they
are used with. That is, if you’re using a 4-40 screw, you need a 4-40 nut. Makes sense.

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