Machining is used to generally describe subtractive processes, usually for metals or high strength plastics, in order to produce parts. Many methods fall under machining, such as milling, drilling, turning, and much more. For example, CNC Milling is a prototyping process in which a spinning cutter removes material using a 3 axis gantry similar to FDM 3D printing.

The Sherman Center Maker Space has a Carbide 3D Nomad CNC Mill. The Nomad can cut wood, plastic, and small metal parts.

Advantages:

1. Strong material choices. Machining can be performed on almost any hard material including metals, woods, plastics, and some composites.
2. 3D geometry. CNC milling offers 3D geometry of strong parts.
3. Clean finish. Unlike other manufacturing techniques, CNC milling provides a very nice looking part.

Drawbacks:

1. Expensive. CNC milling is very expensive in terms of material since the starting stock needs to be larger than the largest dimensions of whatever part you are making.
2. Geometry. Not all geometries are able to CNC machines since the cutter can't access undercuts. For these operations, 5-axis CNC machines are required.
3. Learning curve. It is really difficult to learn to cut complex parts using a CNC mill. It requires knowledge of CAM (Computer Aided Manufacturing) which is the planning and execution of material cutting.

Part Design:

When producing parts for machining, there are certain design considerations that should be implemented. Performing proper DFM for machined parts ensures ease of manufacturing, and establishes if machining is even the correct method in the first place. There is a vast amount of information and resources online, but these are some of the most common principles to apply/consider.

The best resource for learning how to design for machining are machinist - talk to the people making these parts, showcase your designs, and ask a lot of questions!

Information from Adam Bender, great site on machining