So the big question is…… What are the different types of CNC router bits? And when should you use each of them?
But first let’s recall all the things CNC routers can be used for…
Each of these operations lends itself to a different type of bit, let’s go through them one by one.
CNC Routers are commonly used to flatten off large slabs that are starting out with an uneven surface. For this, you want a flat-ended cutting tool that gives a nice surface finish. The ideal bit for this would be either a fly cutter or face mill. Both of these have a wide diameter and blades facing downwards and outwards.
Something of note is that the cut depth that a fly cutter can handle well is small compared to other bits. It often takes multiple passes to fully flatten a piece. The increased width of the bit can also be limiting, this is also why you really wouldn’t use these bits for carves that go any deeper than just the surface.
Cutting those deeper pockets and lines has a different set of bits: endmills. Endmills kind of look like drill bits, but instead of making holes, the blades of an endmill face outwards – not downwards – making them effective at cutting side to side.
There are three main types of endmills: “Flat” endmills, “round” or “ball” endmills, and “radius” endmills, which are a combination of flat and round – they have a mostly flat bottom, but have rounded edges. Flat endmills are very good for creating tracks, pockets, or following paths that go side to side, rather than up and down.
Using a flat endmill is perfect if the bottom of your carve is also flat or has steps in height. Also, because the cutting edge goes along the entire shaft of the bit, you can make pretty deep cuts.
If you wanted a rounded or convex face, you are better off using a round endmill. The circular shape of the endmill allows the tip of the endmill to be hitting the cutting surface at only one point and then curving outwards into smooth arcs and surfaces.
Realistically, these two tools are often used in conjunction: The flat endmill is very good at removing material, so you might use it to make a rough cut of your form, and then go in again with the round bit to smooth everything out.
To give a more specific example, if you were making a bowl on the CNC, you would use the flat endmill to gouge out most of the material, but the inside of the bowl would not be smooth, it will have steps. You would run the ball endmill over those to remove the jagged inside and get the smooth bowl shape you want.
The next CNC operation that we talked about before is drilling. You could use an endmill for this, but it wears out the bottom cutting edge faster than necessary. The best CNC bit for this technically would be a drill bit. However, to be honest we often use our endmills for this too.
This brings us to the last type of bit we are going to talk about today: V-Carve Bits which are great for detailed lettering and Chamfers. This bit is cone-shaped which is perfect for very fine work because the ends come to a point. Therefore it can handle even the tiniest of details that the other types of bits we’ve covered just can’t.
If you trace text with a v-carve bit, it makes for some pretty fancy looking lettering and if you vary the depth of the cut along the path, you can even make calligraphy-style lettering, widening at certain parts of the letters.
They can also cut chamfers. All you have to do is set the machine to run along the edge of a cut and viola.
Every single bit we have talked about come in varying diameter, material, length, angle and radius to suit your needs. Big, small, it’s pretty self explanatory and really just a case-by-case thing.
The last consideration in these bits is the material of the bit itself. There are two main ones worth talking about: High speed steel and tungsten carbide. High speed steel is good for softer materials. It tends to have a slightly shorter tool life than carbide, but is less brittle, so it can be more flexible against messed up cuts. Tungsten carbide is much harder, often used on metals or ceramics. It has a longer tool life, and more temperature resistance, but is much more susceptible to brittle fracture. You can get carbide-coated steel bits that are less brittle, but have increased hardness.
There is one other type of material: diamond tooling, which is used primarily for cutting rocks, but you don’t see that very much for shop CNC routers… it does exist though so we figured we’d throw it in here.
That was our rundown of the different types of drill bits commonly used in a CNC Router.
If you have a topic you would like to see us chat about on a future Maker 101, leave it in the comments below!