STRAIGHT CUT BITS

A straight router bit cuts a straight vertical wall into your material, which makes it the tool for profiling parts, clearing pockets, and cutting dados, rabbets, and square grooves. It is the most used bit type on most CNC projects since almost every design needs a clean, straight cut somewhere. 

A downcut bit spirals so it pushes chips and fibers downward, which leaves a clean top edge with very little fuzz. That makes it the better choice when the top face of your workpiece is the show side. The tradeoff is that chips pack into the bottom of a deep cut instead of clearing, so downcut bits are best for shallower work and clean surface edges rather than deep slots.

An upcut bit has a spiral that pulls the chips up and out of the cut. That chip clearance keeps deep dados and grooves from packing with wood dust and helps the bit run cooler, though it can leave a little fuzz on the top edge. Reach for an upcut when you are cutting deep or want the cleanest bottom in a groove.

Cutting wood makes fine dust, so basic personal protection matters. Wear a dust mask when you run longer jobs, since breathing wood dust over time is bad for you, and keep your work area clear so chips do not build up around the bit. A dust shoe on your machine and vacuum table will catch most of it. 

Yes. A straight bit cuts a full-depth pass through plywood, hardwood, and MDF, though on anything more than about a quarter inch you get cleaner results and longer tool life by cutting in a few passes rather than one. A downcut spiral is the usual pick here since it keeps the top edge crisp, and if the bit is drilling-capable it can also plunge straight down to start a pocket. Match your total depth and pass count to the bit and the material, and let the chipload calculator set your feeds.

The two biggest factors are the bit and your feeds and speeds. A sharp solid carbide bit leaves a smoother cut than a worn or cheap one, and unlike freehand work on a router table, a CNC holds the exact same depth and path on every pass. A downcut spiral keeps the top edge crisp on plywood and solid wood. Beyond that, running the right feed rate for your material does most of the work, since going too slow burns the wood and too fast leaves a rough wall. Our chipload calculator gives you a solid starting point.