Page 81 - Making things move_ DIY mechanisms for inventors, hobbyists, and artists

62 Making Things Move

Material FIGURE 3-8 Counterbores (left) and
The last thing to worry about when countersinks (right) allow screws to sit flush
with the surface.
choosing screws is material. The vast
majority of the ones you use will be steel.
Choose stainless steel if you don’t want
the screws to rust. A plain steel screw
with a zinc-plated or black-oxide finish
will also protect from rust and might be
cheaper than the stainless steel option.

Threaded Rods and Speciality Screws
Threaded rods, or all-thread, are like long screws with no head. You can get them full
or partially threaded and in many different lengths and sizes. One can act as a shaft to
align multiple parts, then sandwich them together with nuts on each side. They are
also used as push-pull rods to create small motions, like steering a rudder on a model
airplane.
There are more types of screws than I have pages to write about them, but a few
deserve a quick mention (see Figure 3-9):

• Shoulder screws have a smooth cylindrical shoulder under the head before the
threads start that is great to use as a spacer or shaft.

• You can use U-bolts to create a loop on an otherwise flat surface.
• Eyebolts serve a purpose similar to U-bolts, but need only one mounting hole
(versus the two you need for U-bolts).
• Self-drilling and self-tapping screws compress the ten-step tapping procedure
to just one step, but are really useful only in wood, sheet metal, and soft
plastics.
• Set screws don’t have a head at all and are great for locating parts on shafts
and connecting gears and couplers to motors (more about that in Chapter 7).
• Binding posts (also called barrel nuts) consist of a screw and a long nut (or
barrel) with a flange on the end. These are great for creating linkages or
sandwiching flat parts together that still need to rotate freely.