CNC routers need bits. They determine the type of carving, the resolution of the finished designs, and the speed at which you can move through the material. They have cutting edges that pull up or push down (sometimes both), they have square or shaped ends, they are designed for speed or accuracy, and they come in diameters from a needle point to over two inches for standard CNC routing.

Choosing the right bits for your CNC router can be confusing. There are many variables to consider when searching for the best bit for you and your project. Here are some important features to consider.

Choose the right router bit shape for your project

Are you making straight cuts in plywood? Then get a high-quality spiral end mill. End mills come in many different diameters. You can choose an upward or downward cut.

Are you carving a large three-dimensional outline or sculpture? You’ll need a ball-nose bit of the right size for the level of detail in your model. Ball-nose (aka contouring) bits are great for 3D carving (think of a topographical map or the grape relief on a wine store sign). (Think of a topographical map or a wine store sign.) You can use just the tip to carve details and smooth contours, or you can move a lot of material like an end mill.

For complex 3D engraving, consider a tapered ball nose bit like this one. A slight angle on the cutting edge can make tool marks parallel to the material surface less noticeable.

If you are flattening a large board, or if you are responsible for maintaining the spoilboard on your CNC router, a spoilboard cutter or flycutter bit is useful. These bits are made to scoop up the surface and leave a smooth, flat finish. I recently upgraded to a 2 1/2″ bit and I love it. Its got four cutting edges and is what is known as an “insert” bit, which means the blade can be removed for resharpening or replacement. It’s an investment bit, but it’s worth every penny. I love to use it to flatten table tops.

Choose the right bit for your material

Hardwood? Plywood? Laminated particle board? Plastic? Aluminum?

Many manufacturers produce bits that are specific to the material. Bits for hardwood are designed to leave a clean edge. Bits for plywood and laminates are designed not to crush the outer veneer layers. Bits for plastics are designed not to melt excessively. Aluminum cutting bits are designed to efficiently remove chips to avoid rewelding (heated chips fusing to the hot cutting tool). Many bits can be used for multiple purposes, so if you are in the prototyping stage of a project, you may not need to purchase 30 bits right away. A good all-purpose bit is a two-flute upcutting spiral bit.