Home Shop Machining/Material

Materials Commonly Worked by Home Shop Machinists
When starting out, Home Shop Machinists quickly figure out that alloys are just that, alloys. Steel is not just steel, aluminium is not just aluminium, etc.. Metals are mixed together to form alloys and each alloy has different characteristics that make it more or less amenable to working with in various ways. Layered on top of this are heat treatments which can dramatically alter a material's properties. For Home Shop Machinists, another important consideration is a material's machinability. This is an actual specification for different alloys, and some alloys are specifically made to be machinable.

Addendum by rkepler: a lot of the choices relate to the old adage: "Anyone can build a bridge that stands, it takes an Engineer to build a bridge that *barely* stands". Many choices can be used outside their particular space - you can make a gun chamber from 1010 if you use a lot of it, but using something like 4140 or 4150 will allow you to make one that weighs less for the same performance and can be hardened to last more than a couple hundred rounds.

Materials by Type
Note that there are multiple standards that define metal alloys, with steel being the most diverse. Where possible, roughly equivalent materials are put under the same bullet. See the comparison chart for more information. The intent is not a comprehensive list of material types but rather a list of what is commonly available and used by Home Shop Machinists.

Mysterium
In the beginning, there is Mysterium, that random bit of stuff that gets clamped down in a machine and worked. Much can be learned from this, it is an economical way to start, but there are drawbacks. Once the basics of operating a machine are settled, the lessons learned working with one type of material do not necessarily transfer over to another. Different materials require different approaches, different tooling, and different expectations on the results. Mysterium has, by definition, unknown properties of strength and hardness, an unknown response to heat, and unknown levels of machinability. These characteristic can, of course, be roughly guessed at by experimentation but that takes time and effort. The last problem with Mysterium happens when it is used successfully. If you want more of the same, it's very difficult to request what you don't know the name of.

Steel
Usually found in both hot rolled and cold drawn:
 * Hot Rolled: Cheaper, has scale.
 * Cold Drawn: No scale, is more dimensionally accurate, but more prone to warping after being machined.

There are many different classification systems... steel has been around for a while. The SAE standard uses a 2 digit number to classify the major alloy and then a 2-digit number for how much carbon is in it. The amount of carbon directly corresponds to how well it will harden, which is useful to know. If there is an 'L' between the numbers it means that lead has been added to make it more machinable. There is probably some sense to the other classification systems... if you can figure it out, then edit this to explain.

Typically found grades:
 * Rebar: Just avoid it, unless you're doing concrete.
 * A36: General purpose hot rolled structural steel. Generally available in shapes like angles, bars, beams, etc.. Easily weldable but difficult to machine.
 * A500: Structural pipe and tubing.
 * 1010, 1018 or S355J2C: Basic mild steel. 1018 has more carbon than 1010 and is thus more hardenable.  Typically, 1010 is found in pipes or square tubes while 1018 is solid stock.
 * 1040 or EN8:
 * 1045 or C45: Round bar stock and key stock.
 * 1144: Usually cold-drawn but specifically made to not warp after machining.  Easy to machine and strong without heat treatment.
 * 12L14: The 'L' stands for 'Leaded' which makes it much easier to machine.  Not weldable.
 * 4140, EN19, or 42CrMo4: A Molybdenum or 'chromoly' steel, usually in a prehardened and tempered grade. For parts that need to be bit harder and tougher. Generally not much more expensive than 1018 yet stronger and easier to machine.  More difficult to weld.
 * O-1 Tool Steel: Oil hardening. Machines fairly well.  Also called 'silver steel'.  Commonly sold as 'Drill Rod'.
 * W-1 or 10951 Tool Steel. Water hardening. Less dimensionally stable than O1. Machines well.  Commonly sold as 'Drill Rod'.

Stainless Steel

 * 304:
 * 308:
 * 316:
 * 17-4 PH: A good choice for stainless steel that can be easily hardened in the home shop, as it only needs to be held at a constant temperature for a period of time then air cooled; a cheap casting pot and salt or lead bath works for this. It machines to a good finish and has high strength, and is widely available in bar form.

Aluminium
Pure aluminum is soft and machines poorly. There are therefor many alloys that add a property such as hardness, workability, etc. The first number of the 4 character designation denotes the primary additive. Some additives interfere with processes such as welding or anodizing.

Cast aluminum alloys have additives that help in pourability and gassing.

Aluminium often comes in specific heat treatments, that '-T#'.

Common wrought aluminum alloys used in home shops
 * 2024: Common aluminum for general machining. More dent resistant than 6061-t6.  Does not anodize well.   Not weldable because of "hot cracking"
 * 5052: The exceptional corrosion resistance of 5052 alloy against seawater and salt spray makes it a primary candidate for marine structures.
 * 6061: cuts well, reasonably hard when heat treated. Weldable
 * 7075: often called "aircraft aluminium".   Can be the hardest aluminium alloy.  Machines well.  not weldable.

Brass and Bronze

 * 360 brass: Free cutting.
 * 660 bronze:

Materials by Task

 * Simple structural shapes being welded together: A36 Steel
 * Simple steel stuff with something other than drilled holes (some machining): 1018, 1026 for more strength.
 * Nice fast turning but not going to weld: 12L14, 1144 if you need some strength, 41L40 if you want nice turning with toughness.
 * Shafting: 1144, 4130/4140 for tough.
 * Springy: 5160 (leaf spring stuff), Makes pretty tough knife blades, better for long stuff like swords.
 * Really springy and hardenable: 1080, 1095. 1095 is clockspring stuff, great for small carving tools.
 * Anything in salt water: stainless: 303 or 304 for low toughness, 316 for tougher and more corrosion resistance, 400 series for hard, 440C for knife blades.
 * Aluminium: 6061 for light duty, 7075 for strong/tough
 * Bronze: SAE 660/C932 for bearings, SAE 68/C952 Aluminium bronze though difficult to machine.
 * High strength bushings and bearings: 954 Alum. Bronze is probably the most popular.
 * Brass: SAE 360 leaded brass for anything to machine. SAE 260 for forming.
 * For general purpose, medium strength shafts: 1045 TGP (turned, ground & polished) is stronger and closer tolerance than cold rolled 1018.
 * Drill rod, oil or water hardened tool steel (O1, W1, etc.). A great choice for the home shop when making a part that needs to be heat treated with minimal equipment, and it machines fairly well too. It can be hardened for cutting tools (blades, reamers, etc) or tempered back for better toughness with good wear resistance.
 * For high strength round parts without requiring heat treating: ETD-150

External Resources

 * Commercial: MetalSupermarket, Choosing aluminum grade
 * Commercial: MetalSupermarket, Available steel grades by shape
 * Commercial: McMaster-Carr, Metals