CNC router bits and endmills

A CNC router bit is the tool a CNC router use while milling a material. This post is about understanding the various CNC router bits available. Such knowledge is very necessary for the successful execution of any cnc machining operation. The choice of bit or endmill can affect the finished look and the processing time for most materials.

We will look at some CNC router bits, their features and how to use them. By the end of this post you will be more informed in choosing the right tool for your project. You will want to have basic collection of bits that will enable you complete most CNC router projects.

CNC router bits types

The most common bits you will need for your CNC projects are:

• Flat endmill
• Ball nose endmill
• V bit

These are the major bits you will need for most CNC operations on your project. Looking at each bit type will show there are varieties in these bit types. The variations are often based on the quantity of chip pulled from the stock material and how those chips are evacuated. Let’s look at each bit type and their variations.

Flat endmill

These are bits that create a flat cut with footprint that is parallel to the xy plane and perpendicular to the tool or z axis. Most tools are mounted parallel to z axis on a cnc router. You will be using the flat endmill for most profiling operations. Most projects will need a profile or contour operation. A through profile will cut all through the thickness of the stock. It is necessary where the final project is smaller than and or has a shape different from the stock.

Flat endmills can be spiral or straight. This is a description of the geometry of the cutting edge along the shaft. Straight flat endmills have the cutting edge running parallel to its shaft in a straight line up to the cutting length of the bit. On the other hand spiral flat endmills have the cutting edge running along the shaft in a helical pattern.

Spiral endmills have three basic types based on the mode of chip evacuation. These are Downcut spiral endmill, upcut spiral endmill, and compression endmill.

Downcut spiral endmills

The Downcut spiral endmill push the chips into the workpiece while cutting. It leaves a good top surface finish and not so good bottom surface finish. There is need for it where the workpiece has the tendency to pull from clamps while using an upcut endmill.

Upcut spiral endmill

The Upcut spiral endmill pulls the chip and the workpiece up away from the CNC table while cutting. This endmill is great in evacuating chips. While cutting a profile through a material, this bit produces a good finish for the bottom surface of the workpiece but not so good for the top surface of the workpiece.

Compression endmill

Compression endmill is a mix of the upcut and Downcut endmill. Its profiling operation starts as a downcut endmill and ends as an upcut endmill. Its major drawback is that it’s not great at chip evacuation while cutting.

Flat endmills produce cuts perpendicular to the xy plane as it cuts deeper into the material. At the end of a through profile cut, it leaves an edge perpendicular to the xy plane. Its finds great applications in extracting the project from the stock material. It’s often the preferred tool for most through profiling operations.

Ball nose endmill

A ball nose endmill has the geometry of a flat endmill with a semi circular tip. This bit creates a hemisphere as a footprint. It has at least two cutting edges called flutes. There are some ballnose endmill with straight flutes used mainly for woodwork. Unlike the flat endmill, the ball nose endmill can be used to mill various types of material to produce rounded cut.

They are most necessary when milling jobs with organic models or designs. Its primarily used in milling 3d reliefs and moulds. The image below is an example of the kind of forms that ballnose endmill can produce. You will most likely use this when milling projects that have 3d design of organic forms.

Vbit

The vbit comes with a triangular tip. It comes in various dimensions of included angle. There are 25, 30, 45, 60, 90 degree angle vbit. These are the most common used for most CNC operations. Vbit creates a footprint that is like an inverted cone. It finds common application in making a miter operations on edges.

One of the most interesting applications of vbit is in engraving with a CNC router. When used for engraving it can be applied in creating v-engraving or v carving designs on selected materials. With the vbit for v carving, the engraved art is deepest where the bounding vectors are most wide apart and shallow when the vectors are close.

The vbit does not create a v carving art just by its geometry. A CAM with the ability to create toolpaths for v carving is essential to obtain the desired output.

Feedrate for bits

Achieving the desired finish depend not just on selecting the right bit but also using the ideal feedrate. Most bits have different feedrate for various materials. The bits are made from metal alloys with which makes them optimal at certain feedrate for a chosen material.

It is best to consult the manufacturer data sheet for each bit with respect to the desired material to be milled. When the feedrate is too high, it could lead to breaking of the bit. Feedrate that is too low can lead to the bit burning out. The spindle speed is also taken into account while preparing your gcode for that perfect finish. Most data sheet will provide the optimal spindle speed and feedrate for the selected material.

I hope as this post will help you as you advance more in your CNC projects and help you to choose right bit for the task. The bits discussed here are by no means the complete list of bits that can be used with a CNC router. However most CNC router projects you will undertake will require the bits discussed above and knowing when to use each is vital.