Selecting which bits to use for a CNC project is a common source of frustration for a lot of new CNC owners, and there’s not a lot of information out there for the beginner. Below are two of the first test projects I did on the Shapeoko. The first one, the letter E, was from the official getting started tutorial. Notice how the sides are all jagged and the line wanders a little? That’s because I had no idea which bit to use, and I wasn’t using the right one. The piece below it was done a few days later with a proper cnc bit, and looks way better.
Which bit you use depends on what kind of material you’re cutting, and what kind of cut you are trying to make. Assuming you’re cutting something relatively soft like wood, plastic, or aluminum, you can use a standard router bit. You’ll want three kinds to start out with- something straight for 2D cuts, something rounded for 3D cuts, and maybe some v bits for lettering or line work.
1) 2D Cuts
A straight, flat bottomed bit is going to be your go-to for cutting out flat parts and general line work. You’ll want a large 1/4 inch bit for cutting large areas quickly, like cutting out the profile of a part. I use this 1/4 inch upcut bit, and it’s great for general milling.
Now that you can cut profiles, you’ll probably find that the 1/4 inch is too fat for cutting out smaller pieces or fine details. You’ll need a smaller bit for that. Grab a 1/16 inch bit like this one. This bit is great because it’s small enough for fine-ish details but still strong enough to do some serious cutting.
2) Fine Details and Lettering
With just those two bits you can probably do all the 2D cutting you need, with the exception of super fine details and lettering. For fine details you’ll want a v bit, which is a bit that tapers down to a fine point. There are tons of different kinds of v bits, with different angles and sizes that are good for different projects. A 60 degree bit like this one would be a good choice for general purpose work.
If you plan on doing any super fine work with tiny details, pick up an engraving bit as well:
3) 3D Contours
Okay, you’re all set for 2D carving. If you want to get into 2.5D or 3D work, you’ll want a ball nose end mill to create nice, smooth contours.
Those 5 bits should be more than enough to get you started. As you do more projects and get more comfortable with your CNC machine you can continue adding to your collection. Good luck!