Page 59 - Making things move_ DIY mechanisms for inventors, hobbyists, and artists

40 Making Things Move

Now scroll down and read through some of the material descriptions. It looks like the
first one, General-Purpose Low-Carbon Steel, is easy to bend, so you choose that one.
You want your toilet paper dispenser to be about 2 in wide, so you choose that option.
Uh-oh—unfortunately, the thinnest piece at that width is 1/8 in thick, which you
won’t be able to cut or bend by hand. So you back up and try choosing a thickness
you know you can cut and bend first, and decide on 0.020 in. Phew! Now your job is
easy, because there is only one option, a 12 × 8 in piece that comes in packs of five.

TIP Sometimes sheet metal is sold in a gage thickness, not a decimal
thickness like 0.020 in. The higher the gage number, the thinner the material.
For example, a 0.030 in thick steel is also called 22 gage, and a 0.060 in thick
sheet is about 16 gage. To convert from one to the other, check eFunda’s
handy online calculator at www.efunda.com/designstandards/
gages/sheet_forward.cfm.

Local metal shops are another great resource, but they may not have convenient
online stores. Don’t be afraid to pick up the phone and ask questions about what
size/thickness/gage/alloy of steel would be best for your project. Most suppliers will be
happy to help you—after all, it is in their best interest to have an informed customer.
Also check out plumbing pipes, fixtures, and electrical conduit as sources of steel
tubing that are much less expensive than more precision extruded material.

Aluminum
Aluminum is less dense than steel and is known for having a great strength-to-weight
ratio. It’s much easier to bend and drill than steel, and won’t rust like plain steel.

A good multipurpose aluminum alloy is 6061. If you want something strong but still
lightweight, alloy 7075 is about twice as strong as 6061 and just as light. It’s actually
stronger than a few steel alloys, and is used in aircraft and aerospace mechanisms.
This means, of course, that it’s generally more expensive, so choose the alloy that is
most appropriate for your application.