CNC machines - the types of CNC machines explained (3 and 5 axis)
In this video you’re going to learn about the different types of CNC machines. We’ll cover the benefits and limitations of each machine, and how they work.
Why is it important to have a good understanding of the different types of CNC machines? Well, If you don’t know the limitations and benefits of a machine, you most likely also won’t know how to design for it properly. And that... could end up costing you a lot of time and money. That’s why today, we’re going to be talking about the different kinds of CNC machines, how they work and what their benefits and limitations are.
Welcome back to another episode in our series: What is CNC machining? In the first episode we briefly talked about different types of CNC machines, and in this video it’s all about exploring them further and going into more detail. At the end you’ll have a great understanding of the different types of CNC machines and how they work.
Before we start
It’s important to note that in this video we’ll be covering CNC machines that remove material using cutting tools, as these are the most common machines and have the widest range of applications. This means that laser cutters, plasma cutters and EDM machines are not covered.
Main categories of CNC machines
Alright, let’s get started! CNC machines can be broken up into 2 main categories or machine types: 3 axis CNC machines and multi axis CNC machines. 3 axis machines are cnc milling or cnc turning machines (also known as lathes). The multi axis cnc machines can be Indexed CNC machines, continuous 5 axis CNC machines and mill-turning machines.
3 axis CNC machines
Let’s start with 3 axis CNC machines. CNC milling machines and CNC turning machines allow the movement of the cutting tool, relative to the workpiece, in three linear axes: left-right, back-forth and up-down. However, it’s good to note that lathes sometimes miss one or more of those combinations.
3-axis CNC milling machines are very common, as they can be used to produce most common geometries. Also, they are relatively easy to program and operate, so start-up machining costs are relatively low.
During CNC milling the workpiece is held stationary directly on the machine bed or in a vice. Material is removed from the workpiece using specialized cutting tools that rotate at very high speeds. The cutting tools are attached to a spindle, which can move along the three linear axes we just discussed. Usually, several rounds of cutting are required to create the desired part. First, an approximate geometry is given to the workpiece, by removing material quickly at a lower accuracy. Then one or more finishing rounds are used to produce the final part.
It’s good to mention that tool acces can be a design restriction in CNC milling. Because there are only 3 axes, certain areas might be impossible to reach. A workpiece can be rotated, so it doesn’t have to be a problem. However, if you need multiple rotations, the labor and machining costs increase fast. Definitely something to keep in mind.
Let’s move on to CNC turning machines, or as they are often called: lathes.
CNC lathes can produce parts at a much higher rate and at a lower cost per unit than CNC mills. This is especially relevant for larger volumes.
During CNC turning the workpiece is held on the spindle while rotating at a high speed. A cutting tool or center drill traces the outer or inner perimeter of the part, forming the geometry. Holes along the center axis can also be manufactured, using center drills and internal cutting tools.
Typically, CNC lathes are used to create parts with cylindrical profiles. That’s also the downside of CNC lathes: this is the only shape they can produce. To overcome this limitation, features of the part are often CNC milled in a separate machining step. Alternatively, 5-axis mill-turning CNC centers can be used to produce the same geometry in one step.
5 axis CNC machines
Now, it’s time for multi axis, or 5 axis, CNC machining.
These machines can rotate on the same 3 linear axis of movement as 3 axis CNC machines. What makes them different is that they can rotate on an additional 2 axes. Making it 5 axes in total. For example, 5-axis CNC milling machines centers allow rotation on the three linear axes of movement. And in addition they can also rotate the machine bed or the toolhead (or both).
Because of this, 5 axis CNC machines can handle more complex geometries. However, the advanced capabilities of these machines come at an increased cost, as they require both specialized machinery and operators with expert knowledge.
If you’re creating highly complex or topology optimized metal parts, 3D printing is usually a more suitable option.
Ok, let’s talk about Indexed 5-axis CNC milling machines and how they work. During machining the cutting tool can only move along three linear axis. However, between operations the bed and the toolhead can rotate automatically, giving access to the workpiece from a different angle. Because of this, no human intervention is needed to manually reposition the workpiece. Parts with more complex geometries can therefore be manufactured faster and at higher accuracy than in a 3-axis CNC mill.
But, they lack the true freeform capabilities of continuous 5-axis CNC machines.
Continuous 5-axis CNC milling systems have a similar machine architecture to indexed 5-axis CNC milling machines. However, there is one big difference: Continuous 5-axis CNC milling machines allow for the movement of all five axes at the same time during all machining operations.
But these advanced capabilities come at a high cost. With continuous 5-axis CNC milling you need expensive machines and highly-trained machinists to accurately program the machines.
Finally, we have mill-turning CNC centers. Mill-turning CNC centers are just like CNC turning machines, only they are also equipped with CNC milling tools. A variation of the mill-turning centers are swiss-style lathes, which have typically higher precession.
How does a mill-turning CNC center work? The workpiece is attached to a spindle that can either rotate at high speeds (like a lathe) or position it at a precise angle (like a 5-axis CNC mill). Second, lathe and milling cutting tools are used to remove material from the workpiece, forming the part.
Mill-turning systems take advantage of both the high productivity of CNC turning and the geometric flexibility of CNC milling. They are ideal for manufacturing parts with 'loose' rotational symmetry at a much lower cost than other 5-axis CNC machining systems.
Alright, we covered most of the CNC machines that use cutting tools. Let’s take a look at some of the most important things we learned about these machines.
3-axis CNC milling machines manufacture parts with relatively simple geometries with excellent accuracy and at a low cost.
CNC lathes have the lowest cost per unit, but are only suitable for part geometries with rotational symmetry.
Indexed 5-axis CNC milling machines manufacture parts with features that do not align with one of the main axes quickly and with very high accuracy.
Continuous 5-axis CNC milling machines manufacture parts with highly complex, 'organic' geometries and smooth contours, but at a high cost.
Mill-turning CNC centers combine the benefits of CNC turning and CNC milling into a single system to manufacture complex parts at a lower cost than other 5-axis CNC systems.
That’s all for this episode on the different types of CNC machines. I hope everything was clear and that you learned something new. Any questions? Put them in the comments and we’ll get back to you as soon as possible. Also, give this video a thumbs up if you liked it and subscribe to our channel so you don’t miss out on future episodes. Until then!