Customers turning to us often ask for CNC machining services when looking to create a metal part with an intricate shape. While using this wide term is common and referring to the exact manufacturing method is not necessary, CNC machining entails two different methods.
They are milling and turning. Both are CNC machining methods but they are not the same.
CNC refers to computer numerical control, meaning that CNC milling and CNC turning use computer systems to guide the cutting machinery.
Good CAD-CAM software can easily translate a 3D model into readable code for the CNC machines. This determines the use and movement of tools, cutting paths, etc.
While our engineers can make the decision regarding suitable operations for a certain part, it could be interesting to know where the difference lies.
What is the Difference Between CNC Milling & Turning?
The short answer is this – CNC milling uses a rotating tool, while CNC turning uses a rotating part for cutting.
So the two use different techniques to create a part. While milling machines create complex parts from blocks of metal by carving away the excess material, turning is commonly used for cylindrical parts like shafts.
What is CNC milling?
Let’s start with milling. First, there are 3-axis CNC milling machines that are more traditional. The cutting tool can move in 3 directions – X, Y and Z axis.
While this sets a few limits to the geometry of the parts, it is enough to complete most jobs that require milling. A wide range of milling tools can provide different cutting methods like end milling, face milling, hollow milling, etc.
Multi-axis milling allows 4 or more axis, including the rotation of the tool and work table. This gives an extra dimension of flexibility. 5-axis milling machines are the most common of these and are able to create pretty much anything that can be manufactured with milling.
The dimensions of the initial block are usually larger than the general dimensions of the final part. Therefore, precision milling is possible for every side. The tolerances are very tight, so reaching a great surface finish is easily doable.
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What is CNC turning?
As said before, CNC turning is used to create primarily cylindrical parts. These can be shafts, custom hollow tubes, conical shapes or any other axially symmetric part.
While 5-axis machining can also create cylindrical parts, turning is just more efficient and the hourly rate for these machines is lower.
The chuck holds the raw material, usually a round bar, in place. The chuck spins along with the spindle at high speeds. The maximum speed, or RPM, depends on the machinery.
The single point cutting tool is attached in a turret. The turret can move to and from the working piece while it is spinning, bringing the tools into contact with metal for cutting.
This highly accurate machining method makes it possible to attain tight tolerances. This is why limits and fits usually go with the hole-basis system, as achieving the required accuracy on the shaft is easier.
While these two are often packaged under the same term – CNC machining – they are not the same. Still, they can complement each other beautifully to produce parts with high precision.
For example, turning a shaft may later need adding features with a CNC mill.
As both find wide use in the manufacturing industry, it is wise to differentiate the two.