Materials #

When you’re in school, you have relatively limited resources. Here are a few families of materials and fabrication methods that you may be able to use.

1. cardboard and foamcore + X-Acto knife and hot glue
2. 3D-printed PLA or TPU, possibly with heat-set inserts
3. laser-cut acrylic, plywood, MDF or chipboard
4. construction lumber + miter saw, band saw, and table saw
5. 80/20 structural aluminum framing + miter saw and drill press
6. sheet metal + tin snips, jump shear, and box brake
7. Aluminum or steel + lathe and mill

Once you get to industry, you have more choices– LOTS MORE.

Aluminum #

There are at least 530 different aluminum alloys. For only $150, you can buy the ANSI H35.1 standard and read all 12 pages (includes appendix).

Alternatively, here are a few guidelines that will help you get your bearings. (That’s almost a pun, but bearings are made of 440C steel, not aluminum.)

• 1100: easy to form, cheap

• 3003: easy to form, cheap, but a little stronger

• 5052: strong, great corrosion resistance, not heat-treatable

• 6061: strong, good corrosion resistance, heat-treatable, machines well

• 2024: very strong, still formable

• 7075: even stronger, less formable, better corrosion resistance

• 7075-T6: the most bad-ass aluminum

Reminder about fatigue: aluminum fatigues; steel doesn’t.

Steel #

Steel = iron + carbon (0.04% - 1.5%)

You can read about different steel alloys in the SAE A29 standard, only $56 for 17 pages (almost 4x cheaper than the H35.1 aluminum standard!).

Generally, the last two digits of the alloy designation are the carbon concentration by mass in hundredths of a percent.

Tool steel #

Materials gallery #

Here’s what these materials look like.

Yield strength tradeoffs #

Notes on material usage, based on notes taken by Ananya Ram (thanks!) #

Plastics: #

• LDPE → milk jug material, cheap
• HDPE → stronger, terrible for the environment, can’t really be machined
• MDPE → recycled material, still terrible for the environment
• Polycarb sheet → like acrylic, but can absorb a lot of energy (high energy toughness)
• Acrylic → can’t machine because it shatters~~
• Delrin → optimized for machining
• Nylon → super strong plastic, some are stronger than steel

Composites #

• Fiberglass → boats, super stiff
• Carbon fiber → also super strong, $$,

Woods: good for lightweight structures #

• Pine → cheapest, lightest, crappiest material
• Cedar → even lighter than pine, eh about everything else. Smells good briefly…
• Fir → Pine 2.0, stiff, tables and long-term stuff
• Mahogany → looks nice, fancy furniture
• Maple → hard, for cutting board
• Red Oak → heavier means stronger, and it’s very strong, good for floors
• Baltic Birch Plywood → plywood = alternating grain
• Purple Heart → one of the densest woods that you can just buy

Metals, usually alloys: #

• Copper → thermally conductive, expensive, not an alloy
• 1018 Steel → crappy steel, still expensive (nice but heavy)
• Stainless Steel 304 → same as mild steel, non-magnetic, doesn’t rust (nice but heavy)
• A2 Tool Steel → air-hardened steel, very uniform, used for knives (nice but heavy)
• 6061 Aluminum → cheapest aluminum engineers use
• 5052 Aluminum → easily formed or welded
• 2024 Aluminum → used for airplanes etc. extra stiff allow
• Brass → copper + zinc(?); mostly used for aesthetic
• Titanium → $84, stiffest material