What’s an “Axis”?
An “Axis” is an imaginary line around which a dental milling machine moves. The purpose of an axis is to provide a reference point for precise controlled motion of the milling machine. All CNC (computer numerical control) machines convert numeric commands into positions on a specific axis. All of the motion commands that a milling machine follows are based on an axis. As your milling machine runs a program, it is controlling each axis individually to create the movements required to mill your units.
Interesting Details about “Axis”:
There are two types of axes: Linear and rotational.
- A linear axis controls all the straight-line motion of the machine. These are usually the X, Y, and Z axes. Typically, X and Y are assigned to left/right and back/front movements of the machine, and the Z axis is used for the up/down movements.
- A rotational axis controls all the turning motion of the machine. Usually, these are called the A and B axis. Dental milling machines that have a 4th and 5th axis usually use A and B to control left/right rotation and back/front rotation.
Dental milling machines don’t all use the same orientation for their axes.
For example: one machine’s X axis may be another machine’s Y axis. The orientation does not affect the functionality of the machine, but it must be precisely represented by the CAM software to generate accurate commands. Commands designed for one type of machine will not work on another type. If a machine interprets a command for one axis on another the results can be quite bad, sometimes resulting in crashing and physical damage to the machine.
The more axes a machine has, the more complicated designs you can mill.
In dental milling machines you need a minimum of 4 axes to mill a crown. This is because the milling operations require X, Y, and Z movements, plus one rotational movement to flip the work-piece. When you add a 5th axis you gain another degree of positional control, thus allowing the machine to “see” more complex shapes.
4-axis vs 5-axis machines:
4-axis machines are typically a bit cheaper to buy than 5-axis, so there’s a trade-off between acquisition cost and capability. As a rule of thumb, a 4-axis machine will get 80-90% of dental restorations milled. If you’re a small lab doing mostly crown and bridge a 4-axis machine will get you there. 5-axis machines will allow you to mill pretty much anything. You can mill taller units in thinner pucks by rotating the design to fit. This can help you save money on materials. You can also mill more complex implant designs because the machine can “see” off-axis geometries and define them. If you’re in the market for a milling machine, consider these trade-offs before pulling the trigger.
Thanks for reading! We hope this break down of the term “Axis” has been of value. Stay tuned next week for another post like this!