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CNC Router Bits: Complete Guide

CNC Router Bits: Complete Guide

CNC Router Bits: Complete Guide

CNC routers are versatile machines that can be used for machining different types of materials.

These machines use a high-speed rotating router bit to produce high-quality products with a smooth surface finish.

Depending upon the physical properties of the material being machined, the selection of router bit varies from one application to another.

But what are the different types of router bits available on the market and what are the factors that determine the appropriate router bit for your application?

This article guides you to select the appropriate router bit for your application by classifying them on the basis of their material, structure, profile, geometry, and application.

CNC Router Bits for Various Applications

The table below summarizes the different bits needed to perform some of the most common CNC machining operations on a CNC router machine. 

ApplicationsRouter Bits
Pocket cutsStraight grooving bits, bottom cleaning router bits, upcut & downcut spiral bits
Surface levellingBottom cleaning router bits, spiral & straight edge flat bottom bits
GroovingStraight grooving bits, V-groove bits, compression cut spiral bits, ball nose bits, upcut & downcut spiral bits
EngravingSpiral & straight edge flat bottom bits, ball nose bits
2D & 3D carvingTapered ball nose bits, ball nose bits
HolesDrilling bits

  Router bits selection based on the applications.

Classification of Router Bits - Based on their Material

Just like the material of your CNC chassis matters a lot regarding the complexity of work it can handle, the same goes with the material of your router bit. 

When it comes to material, there are three main types of router bits: High-speed steel (HSS) router bit, carbide-tipped router bit, and solid carbide router bit. 

HSS Router Bits

HSS bits
HSS bits

HSS router bits can withstand high temperatures, which means the bit will retain its strength even during long machining periods.

These bits are comparatively cheaper than the carbide-tipped and solid carbide bits. 

However, HSS router bits are prone to wear and can lose their sharpness easily.

Due to this reason, these router bits require regular sharpening, and diamond hones work pretty well for sharpening HSS bits.

HSS tools are recommended for working with lightweight plastics like PET, ABS, PVC, and softwoods like pine and cedar.

Carbide-tipped Router Bits

Carbide tipped router bits
Carbide tipped router bits

Carbide-tipped bits have the reputation of retaining their sharpness for a longer period and can withstand high temperatures during cutting.

This results in long tool life and eliminates the need for regular sharpening of the tool.

The visible difference between the cutter and shank of the carbide-tipped bit appears because it consists of chunks of carbide brazed onto the steel body of the cutter. 

This reduces the cost and improves the tool life as it provides the strength of carbide at the cost of a steel core.

Carbide-tipped bits are recommended for the machining of hard plastics (like acrylics and polycarbonate), hardwoods (like maple and teak), and nonferrous metals (like aluminum, brass, and copper). 

Compared to HSS tools, these tools are slightly expensive.

However, the higher initial cost is accompanied by low maintenance, thereby saving time and improving productivity.

Solid Carbide Router Bits

Solid carbide router bits
Solid carbide router bits

Solid carbide router bits like the tungsten carbide bits are more expensive than HSS and carbide-tipped router bits.

These bits offer high wear resistance and better hardness, enabling them to be used with minimum maintenance.

Solid carbide router bits provide better workability with hard plastics (like acrylics, PVC), MDF, and soft metals (like aluminum, copper, brass, and zinc) while improving the quality of the cut.

However, these tools are very brittle, and extra care should be taken when using them.

Especially, machining ferrous metals like cast iron and steel can put an extensive load on the router bit and cause it to break.

For processing hard metals like cast iron and steel, it is recommended to use polycrystalline cubic boron nitride (PCBN) or polycrystalline diamond (PCD) router bits.

If you are looking for recommendations about the best CNC bits based on their use cases, you can refer to this article - Best CNC Router Bits.

Classification of Router Bits - Based on their Flutes

Flutes are the cutting edges of a router bit.

The higher the number of flutes, the higher will be the strength of the bit to deliver high cutting force and the higher will be the maximum feed rate that the router bit can withstand without breaking.

However, more flutes result in less space for chip clearance, which limits the ability of the bit to remove a large volume of material.

Router bits with 1-flute facilitate easy chip removal at the cost of the strength of the bit to withstand high cutting force.

Most router bits are generally available in 1, 2, or 3 flute configurations.

1 and 2-flute bits are used for applications where soft materials (like plastics, aluminum, copper, etc.) are to be cut.

3-flute bits are used for cutting hard materials.

Depending upon the shape of the flutes, these router bits can be classified into two types.

Straight Flute Router Bits

Straight flute Router bit
Straight flute Router bit

In straight flute router bits, the cutting edge of the tool is parallel to the axis running through the center of the tool's body (or shank).

These bits are generally used where less material is to be removed with a high surface finish.

The straight flute design of the bit does not facilitate chip clearance and is therefore not recommended for applications involving deep cuts, like drilling.

These bits are comparatively cheaper than spiral flute bits.

Spiral Flute Router Bits

Spiral flute router bit
Spiral flute router bit

Spiral flute bits consist of helical flutes inclined at an angle with the axis running through the center of the tool's body (or shank).

The inclined flutes facilitate easy removal of the chip and are therefore used to make deep grooves and cuts.

These router bits are generally used for machining wood, aluminum, and plastics.

Classification of Router Bits - Based on their Profile

The profile of a cut is the shape created by the cutting action of a router bit.

The bits that fall under this category are generally known as special router bits or three-dimensional irregular router bits and are used for joinery, engraving, and mortising applications.

Special router bits have a specifically designed cutting head that is welded to the shank of the tool.

These bits are identified by their unique shape acquired due to their bigger cutting head diameter than the shank diameter.

What's so special about these router bits? The answer lies in the end results provided by these bits, used for adding impressive finishing touches to the woodworking items. 

The significant difference between various special router bits is the shape of the cut produced by them.

Depending upon the profile of the cut, there are various special router bits available for different applications.

Straight Groove Bits

Straight Router Bit and wood
Straight groove bit

Straight grooving bits are very popular in joinery and mortising applications and can have a single or a double cutting edge. 

These bits are recommended for making square cuts and are generally used for making mortise and tenon joins.

Furthermore, these bits are also used for making groves, dado, and L-shaped cuts along the edge of the wood.

V-Groove Bits

V groove router bit
V groove router bit

V grooves bits have a pointed tip with a rounded shank.

These bits are primarily used for engraving designs and making signs on the flat surface of a wooden board. 

Depending upon the diameter and tip angle, these bits can be used for various applications.

Pointed tip v-groove bits are used for making deep cuts in the wooden board, whereas flat bottomed v-groove bits are used when shallow cuts are needed.

As the pointed tip bits can produce fine cuts, these bits are also used for lettering applications.

Rabbeting Bits

Rabbetting bit
Rabbeting bit

These bits leave an L-shaped dado when passed along the edge of the wood, suitable for forming rabbet joints. 

A bearing is provided at the tip of the bit, which helps in guiding the tool while routing and the depth of the L-cut depends on the size of the bearing. 

These bits are generally used for cabinetry work.

Notched Bits

Notched bit
Notched bit

These bits are provided with notches around the periphery of the bit that forms alternating projections along the edge of the wood to be joined.

The alternating projections provide an interlocking surface suitable for joining two wooden pieces with glue or some other adhesives.

These bits are also used for forming squared or mitered projections with 90 deg and 45 deg angles, respectively.

Flush Trim Bits

flush trim bit
flush trim bit

Flush trim bits are used for woodworking applications where both straight and curved edges are to be cut.

These bits are also used to trim off extra projections from the edge of the wood so that the two pieces of the wood flush fit each other. 

The pilot bearing provided at the top of the bit assists in attaining a smooth and controlled cutting process.

Rounding Bits

Rounding Bits
Rounding Bits

A rounding bit is used to fillet the edges of the workpiece.

These bits are used when sharp corners and edges are to be transformed into smooth, rounded edges and are generally used for corners with an edge angle of 90 deg. 

There are two types of rounding bits: single rounding and double rounding.

Single rounding is used for applications where only half the edge is to be rounded (quarter round edge).

Whereas, the double rounding bit is used for rounding the edge along its entire thickness (full round edge).

Chamfer Bits

30 deg Chamfer router bit
30-degree Chamfer bit

Chamfer bits are used to make bevel cuts along the edge of the workpiece.

These types of angled cuts are generally meant for making boxes.

Depending upon the chamfer angle, there are three types of chamfer bits: 45 degrees, 30 degrees, and 22 ½ degrees. 

The 45 degrees chamfer bit is used when making a four-sided box.

For a six-sided box, the 30-degree chamfer bit is recommended.

Whereas for an eight-sided box, the 22 ½ degrees chamfer bit is suitable. 

Roman Ogee Bits

Roman ogee
Roman ogee bits

In architectural language, the word 'ogee' refers to the 'S' shape.

These special bits are used to carve out serpentine profiles along the edge of the workpiece. 

An ogee cut leaves two straight cuts at the top and bottom with an 's' shape in between them. 

There are two types of ogee bits: the classical ogee bit and the double ogee bit.

The classical ogee bit is used to carve single 'S' shaped edges, whereas double ogee carves out a shape similar to two 'S' figures written in continuation.

Cove Bits

Cove bits
Cove bits

Cove bits are used for carving out a concave profile along the edge of the wooden workpiece.

This router bit is popularly used in applications such as making stools, tables, and window seals.

Cove bits are generally used along with round bits, where the round bit carves the male profile and the cove bit carves the female profile of the joint.

Bottom Cleaning Router Bits

Bottom Cleaning router bit
Bottom Cleaning router bit

These bits are also known as surfacing bits and are specially designed for wood planning operations. 

The tool plunges into your work surface and clears out the contour in the desired shape.

These bits are also used to aggressively remove the material for cutting out pockets. 

Tungsten carbide tipped bottom cleaning bits are recommended for working with materials like MDF, wood composites, plastics, acrylics, and PVC.

Classification of Router Bits - Based on their Tool Geometry

The tool geometry defines the shape of the cutting head of the router bit.

Depending upon the geometry of the cutting head, there are various router bits that are used for different applications.

Flat Bottom Bits

Flat bottom bits
Flat bottom bits

As the name suggests, the bottom of these bits is flat, making them suitable for surface milling operations.

Furthermore, the side-cutting edges of these bits make them suitable for engraving processes.

There are two types of flat bottom bits: Spiral edge flat bottom and Straight edge flat bottom bits.

The spiral edge flat bottom bits are recommended for engraving metals.

Whereas the straight edge flat bottom its are suitable for engraving wood.

Ball Nose Bits

Ball nose router bits
Ball nose router bits

The ball nose bits are also known as ball nose mills.

These bits provide the flexibility to perform milling with a large corner radius, grooving, and engraving with semi-circular depressions. 

Detailed and complex 3d carvings can be achieved with these bits as the curves produced by these bits are smooth with a good surface finish. 

These bits are specified by their tip radius, and the lower the tip radius, the better the resolution of the 3D carving will be. 

Tapered Ball Nose Bits

Tapered ball nose router bit
Tapered ball nose router bit

Due to the tapered profile, these bits are more sturdy than flat bottom bits and can dive deep into the material. 

These bits are suitable for both 2D and 3D carving works and can easily handle wood, wood composites, plastics, and several soft metals like aluminum. 

The three flute design of these bits minimizes chips and dust accumulation to a great extent.

Furthermore, for various wood and plastic applications, these bits can remove a large volume of material in a single pass, thereby avoiding the need for multiple passes.

Corn Teeth End Mill Cutters

Corn Teeth End Mill Cutters
Corn Teeth End Mill Cutters

Having multiple teeth around the periphery of the cutter, these bits are well suitable for working with hard materials like PCB, HDF, HDF composites, carbon fiber, fiberglass, etc. 

Additionally, these bits provide good rigidity and are not easily breakable. 

For applications involving long machining hours on hard materials, it is recommended to use tungsten steel solid carbide bits, as they provide good resistance to wear and high temperature.  

Classification of Router Bits - Based on their Type of Cut

The direction of the cut plays a vital role in determining the surface finish of the cut.

Depending upon the type of material to be cut, an upcut, downcut, or compression cut spiral bit can be used.

Upcut Spiral Bits

Upcut spiral bits
Upcut spiral bits

Upcut spiral router bits are used for slotting and grooving applications because of their ability to perform smooth cuts with a high surface finish.

During routing, these bits pull the chips away from the surface and are hence recommended for thick materials.

When using this bit for machining thin and soft materials, the chip pulling action of the bit renders the top surface rough and ragged.

Furthermore, the upward pull generated by these bits during routing can pull the weakly-held soft workpiece out of the clamps.

These bits are recommended for cutting slots for keyways and other joinery applications that involve cutting smooth slots in the workpiece.

Downcut Spiral Bits

Downcut spiral bits
Downcut spiral bits

Unlike upcut spiral bits that pull the chip away from the surface, these bits force the chip towards the surface of the workpiece.

This results in minimal upward force and therefore produces a good surface finish when machining soft and thin materials.

However, these bits are not recommended for drilling or routing thick materials due to the accumulation of the chips around the cutting area, which can clog the cutting tool.

Furthermore, using these bits for machining thick materials will result in a rough surface that requires additional machining operations to smoothen the surface. 

Compression Cut Spiral Bits

Compression Cut router bit
Compression Cut router bit

When working with double-sided laminates like ply or melamine, a good surface finish is desirable on both the front and back surfaces of the workpiece.

The compression cut spiral bit is an excellent choice to achieve this.

These bits are a combination of both the upcut spiral and down-cut spiral cutters. 

They have complex flute geometry, which pulls the material from the bottom surface while simultaneously pushing it towards the workpiece from the top surface, thus providing a smooth surface on both sides. 

One-third of the bit has an upcut geometry while the remaining two-thirds has downcut geometry.

Therefore, running these bits at full depths is recommended to get the optimum results. 

Drill Bits

Drill bits
Drill bits

Drill bits are commonly used with CNC drilling machines for making holes in wooded and metallic workpieces, generally suitable for screwing applications. 

There are various diameters of drill bits to choose from, which allows flexibility to use these bits to make holes of different sizes. 

Drill bits don't have side-cutting edges, so they cannot cut laterally like milling bits.

Therefore, to avoid breaking the drill bit, make sure not to operate the X and Y-axes of the CNC machine during the drilling operation.

Frequently Asked Questions (FAQ)

What material is best for a router bit?

Steel and carbide are the best materials for a router bit that are commonly used because of their high temperature, wear resistance, and ability to deliver high cutting force without snapping.

What is the advantage of a spiral bit over a standard straight bit?

The spiral bit provides a comparatively smoother surface finish than the straight edge bits because spiral bits perform the cut with a shearing action. 

How to improve the surface finish of the uphill side when cutting curved paths?

The best way to improve the surface finish in woodworking is to make cuts along the fibers of the wood. Performing the cut against the fibers will result in a rough surface finish of the cut. 

About John

Hey I'm John. I talk about CNCs and Lasers at Mellowpine. If you have any questions related to CNCs or Lasers, I'd be happy to answer them. Reach me at mail@mellowpine.com

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John

Hey I'm John. I talk about CNCs and Lasers at Mellowpine. If you have any questions related to CNCs or Lasers, I'd be happy to answer them. Reach me at mail@mellowpine.com

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