CNC stands for "computer numeric control". CNC machines use computer-generated numeric code to execute actions. Lots of these actions are physical movement of one or more axes. Depending on the sophistication of the machine and the computer program writing the code, the axes may move simultaneously and with varying speeds. Cutting tools like drills and endmills are employed within the machine. These tools are often spinning and are used to remove material from a piece of stock material which the machine operator fixtures a certain way. When you combine spinning cutting tools with multi-axis movement and multiple sizes and types of cutting tools within a single machine, you are able to produce complex shapes and features. CNC machines are often very precise and can make cuts accurate to less than .0005" (five ten thousandths of an inch).
There are two main types of machines that can perform CNC machining. Lathes and mills. The main difference between the two is that a mill has the stock material fixed in place and the machine has spinning cutting tools that move around and up and down in relation to the material. In a lathe, the tool is stationary and the stock material is spinning. For this reason, lathes are generally the best option for parts that are round and mills are great for everything else. However, there are also machines that gray out the lines between the two; mills that can make round parts and lathes that make parts that aren’t round. We’ve got machines available that can do this, that, and everything in between.
CAD stands for "computer assisted design." This refers to computer software that allows you to digitally construct 2 and 3-dimensional models that can be then sent to a 3D printer or imported into CAM software for manufacturing. One of the most popular CAD software packages is Solidworks.
CAM stands for "computer assisted manufacturing." This is computer software that uses CAD models or other created geometry to map out paths, tools, and settings for a CNC machine to use when making a part. The CAM program selects these parameters and then creates a numeric code file that is loaded into a CNC machine. The operator then carefully sets up the machine with the appropriate settings and tools to safely and correctly execute the code. Two common CAM software packages are SolidCAM and Mastercam.
3D printing is a process by which plastic (and even metal sometimes) is deposited or bonded layer by layer until a desired 3-dimensional part is created. This is known as "additive manufacturing" because you're adding material on. Conversely, machining is considered "subtractive manufacturing" because you are removing material to get a finished part. 3D printing often takes much longer than machining to produce an identical part as is not as accurate. But sometimes you need a part with a shape or features that simply are not economical or possible to machine. 3D printing in plastic is also generally cheaper than machining from the same plastic.
“Tolerance” refers to the amount of error or allowance a certain dimension can have on a part. For example, if you need a 3ft board for a simple construction project, you could probably cut it .5” oversize or undersize and it would still work just fine. Conversely, if you want to press fit a bearing into a hole, you will need a much tighter tolerance, often times +/- .0005” (five ten thousandths of an inch) or smaller. Smaller tolerances generally drive up the cost of a part because the programmer, operator, and inspector will have to put more effort and time into making and verify those critical dimensions. For CNC machining, generally accepted and reasonable tolerances for standard parts is +/- .01” (ten thousandths of an inch) or +/- .005” (five thousandths of an inch). If you want features cut to tighter tolerances than this, it may increase the quoted price of your part.
GD&T stands for "geometric dimensioning and tolerancing.” This is the process and standard of establishing the form and shape of a part and controlling it. For example, you may want a flat, rectangular part to be anywhere from .125” to .25” thick, but you want both sides to be very nearly perfectly parallel to each other. A simple thickness dimension with a large tolerance could not control this because one side could be .125” thick and the other could be .25” thick and it would still meet the thickness tolerance. Instead, you can add the GD&T control of parallelism which specifies that the two sides must be parallel within a certain range set by the designer, regardless of the part thickness.
The acronym CMM stands for “coordinate measuring machine.” This is a machine, computer or hand-operated, that uses a probe to establish an origin point on the part you are measuring. Once it knows where that point is, it moves around and uses the probe to measure the location of other points on the part. Because the machine tracks all of it’s movements, it is able to determine the location of these points. This allows you to measure features, dimensions, and even the form of a part that you might not otherwise be able to measure. CMMs are generally very accurate, with some being accurate to less than .0002”!
With the right tools and settings, just about any material can be machined. Anything ranging from soft plastics like UHMW to harder plastics like Delrin and PEEK. Metals such as copper, brass, aluminum, steel, stainless steel, and titanium can be machined with proper tools and machine parameters. The most common plastic to machine is Delrin and the most common metal is aluminum.