Page 85 - Making things move_ DIY mechanisms for inventors, hobbyists, and artists

66 Making Things Move

You need to carve a slot in a shaft to hold retaining rings in place, but this is easy to
do if you have access to a lathe. See Chapter 9 if you want to know more about
lathes.

Permanent Joints: Glues, Rivets, and Welds

Permanent joints are used when two pieces are designed to go together and never
need to come apart. This includes welds, rivets, glues, and epoxies. Although a glued
joint is quick and easy, permanent joints can cause headaches if something goes
wrong and you need to take things apart. Permanent joints are a last resort. Consider
using nonpermanent joints first.

Adhesives

Adhesives come in many different forms, from the common white Elmer’s glue we
all used in elementary school to two-part epoxy. They can take anywhere from a
few seconds to a week to dry and reach full strength. Some are designed to join
similar materials, while others can be used on dissimilar materials as well. (Go to
www.thistothat.com for some good advice on which adhesives to use based on
what you are gluing together.)

As a rule of thumb, make sure both surfaces are clean, and give them texture with
some sandpaper or a file to give the glue more surface area to grab.

Wood Glues
Wood glues should be used to join wooden pieces along the grain. When used this
way, the bond is very strong—sometimes stronger than the wood itself.

Common white multipurpose Elmer’s glue will work for wood, but yellow wood glue
is better suited for most applications. With yellow glue, you have about 15 minutes
from when the glue leaves the bottle to when it starts to dry.

The next step up is Titebond II, which you should use if you need water resistance, a
tackier working material, and a faster setting time.
Finally, there are polyurethane foam glues (like Gorilla Glue) that react with moisture
to expand and fill gaps and crevices and dry to form extremely strong joints.