5-Axis CNC Routers

This year I went to IWF Atlanta with the same objective as I did two years ago. That is, to research the 5-axis routers offered for sale. While I think all of us have some familiarity with CNC routers, I’d like to briefly describe the operation of these remarkable machines. I’d also like to describe the anatomy of CNC routers as they most commonly apply to woodworking.

CNC routers are controlled by numeric input which is communicated to the router through a computer. In fact, “CNC” is an acronym for “Computer Numeric Control”.   But to make communication with the router reasonable for most humans, software has been created to translate human perception into machine code.

The most effective interface with humans starts with a “CAD” drawing; “CAD” is an acronym for “Computer Aided Design”. As the name indicates, the drawings are created using computer software. They can be 2-D drawings or 3-D models. 2-D drawings are adequate for simple, rectilinear products. 3-D models are far better for complex products since they show the complete geometry of the part; no dimensional information needs to be entered manually.

So taking a CAD drawing of a product, individual part drawings are separated and imported into a “CAM” program (“CAM” is an acronym for “Computer Aided Manufacturing”). This process is more straightforward if the drawing is a 3-D model rather than a 2-D drawing.

Also, a ‘post processor’ is provided for every CNC router. It contains configuration information specific to that particular machine. This information is entered into the CAM program. As tools are installed on the machine, the CAM programmer enters the information that pertains to each tool. He also determines appropriate feed rates, spindle speeds, etc. All this information is necessary for the machine to process the parts correctly.

There’s a lot going on there. However, the post processor is only installed once for each machine unless the configuration is changed for some reason. Also, tooling information only needs to be updated when new tools are introduced or parameters of existing tools are changed.

Also, when 3-D models are used, the CAM program can read all the geometric features of a part and even select the right tool to machine each detail in many cases. So the actual programming time for each part can be very short, especially when parts are similar to one another.

Next, I’ll explain the anatomy of CNC routers.

The most common CNC router used in woodworking is a 3-axis vertical router. By vertical, I mean that the router head is oriented vertically. The 3 axes are named “x”, “y”, and “z”.   Along each axis, the router can move in a positive direction or in a negative direction. The most common setup is to have the x-axis move left and right when you’re facing the machine from its front. The y-axis movement is toward you and away from you. The z-axis movement is up and down.

What makes CNC routers so versatile is that the router can move simultaneously in all 3 directions. The relationships of movement between the axes can be continuously changing. This is called “3-axis interpolation”.

As a result, these routers can machine anything from rectilinear parts to parts that contain compound curvature. For example, they can create a “domed” surface. The abilities of 3-axis machines are somewhat limited, however, since the router head always remains in a vertical orientation.

The next step up is a 4-axis machine. These machines add the capability of rotating the orientation of the router head. This rotational axis is referred to as the ‘C’ axis. It doesn’t help much until you acquire a special type of “aggregate” head that can change the orientation of the vertical spindle to different angle. The angle has to be set manually so each time you need a different angle, you have to reset it to the new angle. But this setup allows you to create shapes that are difficult with a vertically oriented spindle. An example is the ability to circumvent a part with the bit always pointing towards the center.

And finally, the 5-axis router can do an enormous variety of shapes efficiently. If we take the ability of that aggregate described above and add the ability to continuously change angles along with the other movements, we have 5-axis interpolation. This additional axis is referred to as the ‘A’ axis. The implications have to be seen in action to be fully appreciated. If you search “5 axis router videos” on the web, you can find numerous examples. It’s amazing to watch them in action.

As I mentioned earlier, this year at IWF I was continuing the research on 5-axis machines that I started two years ago. I needed to find the best price for an appropriate machine for a client of mine. When I investigated the prices at IWF two years ago, almost all 5-axis machines were $200,000 and up. This year, we discovered that a good number of vendors now offer a 5-axis machine for less than $170,000, some as low as $150,000.

5-axis routers are not the most efficient machines for high production of cabinet parts or similar items. However, significant benefits are realized when machining certain types of products. Some of the following features of parts indicate where a 5-axis machine may be the best choice:

  • Parts that require machining from various directions and angles, such as sculptures
  • Parts that contain a significant variety of angled surfaces such as miters other than 45 degrees
    • The variation of angles doesn’t necessarily need to be present on each part to make the 5-axis machine the best choice. It may be a matter of not having to change tools between parts. Changing a tool is a time consuming process if you run out of room on your tool changer. A 5-axis machine can use one tool to machine surfaces at variety of angles.
  • Parts that contain smooth surfaces with curvature in more than one direction

So if the geometry of your product warrants it, the 5-axis router may be well worth the investment.