Page 57 - Making things move_ DIY mechanisms for inventors, hobbyists, and artists

38 Making Things Move

You will almost always find that more precise materials with tighter tolerances are
more expensive. It takes more work to make a metal rod that is 0.5 ± 0.001 in than it
does to make one that’s 0.5 ± 0.010 in. If you don’t need perfection, don’t ask for it!
You will pay the price if you do. Words like precision ground and tight will get you
tighter tolerances and very straight, flat material, but only spring for them when you
really need them. On the other hand, oversize parts guarantee they will always be
bigger than the standard dimension you choose.

Material Types

There are three main types of solid materials: metals, ceramics, and polymers (plastics).
Three other categories are useful to define: composites (including wood), semiconductors,
and biomaterials.

Metals

Metals can be pure, as in the case of pure aluminum or iron, or alloys, like steel. An
alloy is just a mix of two or more metals. Metals are generally good conductors of
heat and electricity. They tend to be strong yet ductile, so you’ll find them in a wide
variety of shapes and sizes.

Your local home-improvement store should have a good selection, and you can look
to more specialized metal distributors, depending on the sizes, shapes, and materials
you need. In addition to our staple supplier McMaster, here are some other places
to look:

• Metalliferous (www.metalliferous.com) sells a good assortment of metals in
sizes and shapes common for hobbyists.

• At Metal Supermarkets (www.metalsupermarkets.com), you can get small
pieces and quantities of just about any metal cut to the size you need, while
you learn from their helpful material descriptions.

• OnlineMetals.com is another great resource, and you can get a 5% discount
if you access the store through the Maker Shed site (www.makershed.com/
v/metals/).
• Speedy Metals (www.speedymetals.com) has a good selection and good prices,
but searching the site is less beginner-friendly than on the preceding sites.