CNC Router Bit Guide: What You Need to Know
CNC wood bits, engraving bits, or metalworking bits, enable your machine to do what it’s made for. Knowing which CNC bits to choose can be confusing, and few people truly understand how they work.
In this article, we’ll take a closer look at:
What are CNC router bits?
Types of CNC Bits
The parts of CNC bits
The materials CNC bits consist of
Drilling bits vs. milling bits
We’ll also delve into some of the other details. For instance, in our sections about materials, we tell you exactly which materials work for which workpieces. The descriptions of the different CNC bits cover what each one does well. Let’s get into it.
What are CNC Router Bits?
CNC bits are the tools that fit into a CNC router’s rotating spindle.
The spindle moves at high speeds, allowing the router bit’s cutting edge to remove a certain amount of material. Every revolution either deepens, widens, or enlarges the cut.
Different bits have different purposes. CNC wood bits, for instance, only cut wood. Depending on the bit in use, you can cut, engrave, or mill wood and other materials.
CNC Bits in Detail: Parts of a Bit
CNC bits may be a relatively simple part of the routing process, but there’s more to them than meets the eye. From CNC wood bits to carbide drilling bits, they mostly share the same basic structure. Most bits, whether they be drill bits or router bits, share the following parts:
Flute - The flute is the cutting edge of the CNC bit that recesses into the core. Without it, the bit couldn’t remove the material it cuts. Much like an earth auger or standard drill bit, the flute scoops up the material the bit removes. It then spins it backward till it ejects at the end of the flute length.
Flutes can be either straight or spiral cut. Straight flutes don’t remove material from the cut, but spiral flutes do.
Pro Tip: More flutes equal a smoother cut, though it reduces the capacity for chip load.
Flute Length - The flute length is the overall amount of space that the flute fills on CNC bits. It’s often a critical criterion when buying bits, and most manufacturers list the flute length on product descriptions.
Land - The land part of CNC bits is the inverse of the flute. It’s a raised ‘island’ between the flutes, which is likely where it gets its name. Unlike the flute, which removes loose material, the land helps provide the thrust needed to cut the material.
Lip Relief - Lip relief refers to the amount of slant on the CNC bit’s tip. It usually makes up the blade edge of the bit, allowing it to cut efficiently.
When you look at CNC bits from the front, the anatomy changes somewhat. From this point of view, you’ll see the:
Land - Same as with the side, the raised part between the fluting.
Margin - How far the cutting edge (lip relief) extends beyond the web thickness.
Web Thickness - How thick the bit is, i.e. How wide the flute part is at the bit’s surface.
Essential Terminology When Dealing with CNC Bits
If you work with CNC bits a lot, there are a couple of phrases you’ll hear a lot. Let’s take a look:
Toolpath: The route the spindle follows to make cuts. You get to program the toolpath into the software when you’re creating the design. It’s worth noting that you can’t program the toolpath to go contrary to the machine’s axes.
Chip Load: The chip load refers to the size of the material that the bit removes with every rotation. Smaller chip loads equate to more heat generation, while larger chip loads lead to the reverse.
Feed Rate: How much lateral space your bit can process per minute. Feed rates are typically measured in inches or feet per minute. If your chip load and feed rate don’t match up, you can easily damage your CNC bits.
Speed Rate: How fast the spindle moves. Speed rates are measured in revolutions per minute, and not all bits can maintain equal speeds.
CNC Router Bits Guide: Bit Materials
CNC bits don’t always consist of the same material. The market features a variety of types, each of which has different advantages and disadvantages.
Not all bit types can cut every type of material, so you need to choose the right bit for your particular project. Let’s take a closer look at the materials used to manufacture these bits.
Solid Carbide (SC)
Solid Carbide CNC bits are some of the harder bits on the market. However, as with many hard materials, they can be brittle.
Carbide is a type of wear-resistant steel that works well for cutting materials like:
PVC
Foam
Wood
Acrylic
Plastics
Fiberboard
Soft Metals
Depending on the shape of the bit, solid carbide can be used for cutting, engraving, and milling among other things.
It’s worth noting that not all carbide bits are equal. If you want CNC bits that will stay the course, you may want to consider paying more for a quality bit.
Carbide Tipped (CT)
High-quality carbide steel bits can be expensive. Carbide-tipped bits make their efficiency available at a lower price.
Carbide-tipped steel bits have a core that consists of cheaper steel, coated with a layer of carbide. This arrangement gives you the affordability of most steels and the strength of carbide.
You can use these CNC bits for all the same things you’d use a solid carbide bit for, namely:
PVC
Foam
Wood
Acrylic
Plastics
Fiberboard
Soft Metals
Styrofoam
Typically, carbide-tipped bits are on the chunkier side, since they have an independently molded core. Hence, if you want to do fine work, a solid carbide bit is the better choice.
Solid Tungsten Carbon
Unlike many other bits, Tungsten-carbon bits are a specifically-alloyed blend of metals. Manufacturers combine metallic cobalt and tungsten carbon to get CNC bits that:
Are more durable
Are extremely strong
Stay sharper for longer
Are harder and less brittle
These CNC bits work well for both soft and medium-hard materials, like:
PVC
ABS
Foam
Wood
LDPE
PMMA
HDPE
Acrylic
Plastics
Styrofoam
Fiberboard
Soft Metals
High-Speed Steel (HSS)
High-speed steel CNC bits consist of hardened steel, which gives them several advantages:
Increased heat resistance
More wear resistance
Greater hardness
Thanks to these advantages, HSS CNC bits can handle some of the materials that other bits struggle with. Some of the materials you can cut with HSS include:
ABS
PVC
HDPE
LDPE
PMMA
Wood
Acrylic
Styrofoam
HSS CNC bits work exceptionally well in any context that requires high resistance. Depending on the type, you can use them for cutting, milling, engraving, or routing.
Polycrystalline Diamond (PCD)
Polycrystalline diamond CNC bits are extremely hard and can cut materials that would never be possible with traditional steels.
These bits consist of diamond particles that have been bound and embedded in a carbide base. Thanks to the extreme strength of both diamond and carbide, these bits are:
Harder than steel
Extremely durable
Better at cutting highly abrasive substances
Thanks to the above features, these bits can cut a more diverse array of materials, like:
PVC
ABS
Foam
Wood
LDPE
PMMA
HDPE
Acrylic
Acrylic
Plastics
Styrofoam
Fiberglass
Fiberboard
Soft Metals
Carbon Fiber
CNC Router Bit Guide: Bit Types
Now that our CNC router bit guide has discussed the different materials of which CNC bits consist, let’s look at the types.
Depending on the purpose you’re using your router for, you’ll need a specific type of bit. The market boasts many different kinds of CNC bits, but we’ll discuss some of the most popular below.
Drilling Bits Vs. Milling Bits
The main distinction between CNC bits is that they’re typically either drilling bits or milling bits.
As the name implies, drilling bits are best for creating holes and drilling straight through materials. Machinists often use them to pre-drill holes for screws, recesses, and other basic holes or pockets.
Milling bits, on the other hand, cover all the other aspects of CNC machining. From engraving bits to routing bits and cutting bits, anything that isn’t a drilling bit falls in the milling category.
If you’re practicing a straightforward drilling operation, then you’ll probably need a drilling bit. For everything else, you’ll need some kind of milling bit.
As you can imagine, there are hundreds of different bit types. Below, we’ll take a closer at the different shapes that CNC bits come in.
Flat-Bottom Bits
Flat-bottom bits, also known as cylindrical bits, come in both spiral and straight-edge varieties. These tools typically find use in engraving and cutting functions.
Spiral bits work better when cutting or routing since it’s the tip of the bit that does the cutting. Straight-edge bits work well when engraving since it’s the straight blade that removes the materials.
Ball-Nose Bits
Ball-nose or round-nose bits have a different sphere of pressure thanks to their arched shape. The pressure applied to these bits is distributed more uniformly, creating a smoother cut.
They’re useful for various tasks, but not for cutting and milling as such. Some of the best ways to use these bits are when:
Creating flutes in solid materials
Routing channels
Engraving
Tapered Ball-Nose Bits
Tapered ball-nose bits give you the best of both worlds, combining tapered bits and round-nose bits.
These tools work well for things like scrollwork, carving, and detailed routing. Thanks to their fine, rounded tips, and taper, these CNC bits produce a uniform cut. They also have small working edges, allowing them to do intensely detailed work with clean edges, no matter how fine the design is.
Corn Teeth End Bits
Corn teeth end bits get their name because the side edges are full of teeth. This can make these CNC bits look similar to corn.
Thanks to their unique design and plethora of cutting edges, these bits work exceptionally well when dealing with tough materials. They often leave a smoother edge since their abundance of cutting edges smooths the working surface.
Irregular Tapered Bits
Irregular tapered bits are CNC bits produced with specific purposes in mind. They’re often referred to as big-head router bits.
Unlike most CNC bits, which have a head welded onto the existing shaft, the heads of these bits are machined from the same piece of material as the shaft.
Depending on the size and shape of the bit in question, the purpose can vary significantly. A few of the uses include:
Cutting
Routing
Engraving
The main use is for this bit type typically engraving, but it all depends on what each specific bit was made to do.
CNC Bit Cutting Types: What You Need To Know
Spiral bits are significantly different from straight bits, even if they look similar. There are three main types of spiral bits, which serve different purposes. Let’s take a closer look at them.
Up-Cut Bits
Up-cut bit pull both the workpiece and the chips it removes upwards. Doing so helps to remove all debris and discarded materials from the cut.
The main advantage of this approach is that it prevents the bits from overheating due to constant friction. Removing the discarded material reduces friction and heat levels.
These bits are great for most tasks and produce a reliably clean cut on the project’s lower surface.
Down-Cut Bits
As you’d imagine, down-cut bits do the reverse of up-cut bits. Instead of pulling upwards, they push the material and debris downwards.
These bits are excellent when trying to produce a clean upper surface, but may leave the lower surface looking ragged.
Because they push the discarded materials back into the cut, these aren’t the best bits for drilling holes. They produce high levels of friction since they keep pushing against the removed materials.
Compression Bits
Compression bits combine the qualities of both up-cut and down-cut bits. They push the upper surface of the workpiece down while pulling the lower surface of the workpiece up.
Thanks to this unique operating method, these drill bits are ideal when working with laminated materials. They can help prevent cracking and warping, leaving a clean surface on both sides of the workpiece.
CNC Router Bit Guide: Choosing the Right Bit for Your Project
When you’re trying to find the right CNC bits for your project, there are a few things you need to consider.
Here are a few questions you can ask yourself to figure out which ones you need:
Are you drilling or milling? If you’re just drilling holes, then a CNC drill bit will suffice. If you’re routing, engraving, cutting, or doing scrollwork, you need one of the milling bits.
Which material are you working with? This affects both the material the CNC bits are made of, and which type of bits you buy. For reference:
Laminated materials fare better with compression bits than up-cut or down-cut bits. It will give you a cleaner cut.
Solid Carbide or Carbide Tipped CNC bits are best when you’re working with extremely hard materials.
If you’re working with hard materials, but not doing anything too fine, corn tooth end bits will work well
If you’re working with hard metals, carbon fiber, or glass, consider buying polycrystalline diamond bits. Diamond is hard enough to cut these materials easily.
If you’re doing fine, detailed projects, tapered ball-nose bits will give you a clean finish. Especially when engraving, carving, and doing scrollwork.
What is the aim of the project? If you’re simply milling something to size, a straight edge up-cutting bit will work well. If you’re making mounting holes for cabinets, a drilling bit will work. But, if you’re doing fine engravings on glass or metal, you’ll probably want a polycrystalline ball-tip bit.
We hope that you’ve enjoyed our CNC router bits guide and that it’s answered all your questions.
If you’re new to CNC routers and other CNC machines, or you’re still in the market for one, check out our 3-axis CNC machines.
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