The CNC Machining Process

Material Removal

The example below demonstrates the procedure for machining a curved surface component, in this case a wing section.


This is the first stage of machining where the object is to quickly remove the bulk of the waste material, normally with the aid of a ripper cutter (see cutters below), this gives the coarse stepped feature seen in the workpiece above.

Semi Roughing

This stage of machining generally uses a smaller cutter than roughing, typically an end mill, although the aim is still to remove the bulk of the waste material.

Semi Finishing

The next stage, using a relatively large ball nosed cutter, is to start to form the final profile of the workpiece, removing the steps generated in the two above procedures.


The final stage, and the longest process of all, is the final cut to the desired size. A small ball nosed cutter traversing across the surface produces the finished shape.

Although this is the final machining stage there is still much work to do in the form of hand polishing and finishing before the article is complete.

Types of cutter

A - Ripper Cutter
Used for the rapid removal of large amounts of metal, the serations along the cutting edge literally rip the material away. This cutter is designed to cut along it's sides only.

B - End Mill
Similar to a ripper only without the serations, used for removing the bulk of the material. The cutting edges, like the ripper, are down the sides of the tool.

C - Slot Drill
Typically this cutter has less cutting surfaces than the two above, and unlike the end mill and ripper can be used to plunge directly into the workpiece. As a result of the reduction in cutting surfaces there is better swarf removal meaning the tool can be used in enclosed pockets and slots.

D - Ball Nosed Slot Drill
This cutter, as its name suggests, has a semi-circular cutting face, with the aid of computer software it is possible to cut tangentially to the work piece enabling curved surfaces to be machined.