From the classroom to manufacturing enterprises, CNC machining and other digital fabrication technologies are helping to augment education lesson plans as well as product development workflows. There’s a valuable use for digital fabrication in almost every industry.
But what are the basics of CNC machining? What do you have to understand about the machine to accurately translate computer design data into the physical world?
We’ve shared some basics about 3D printing. Now, here’s what you need to know about CNC machining.
Basics of CNC Machines and Tooling Geometry
A computer numerically controlled (CNC) milling machine is used to transform blocks of raw stock into finished parts by cutting away material.
There are generally three axes to a milling machine:
Basics of a milling machine.
For the purposes of this discussion, we will consider the following directions when referring to the orientation of operations and tools:
X axis: Left to Right (Sideways as viewed from the operator’s position)
Y axis: Forwards and Backwards (As viewed from the operator’s position)
Z axis: Up and Down (Vertical as viewed from the operator’s position)
These three axes of motion let the spindle, which spins a cutter at high speed, carve away material and leave behind nearly any shape desired.
The part being milled is held in a vise, which is in turn attached to the table of the CNC.
Types of CNC Machine Cutters
But not all CNC machines are built the same way. There are different cutters or endmills. Here are some common types:
Flat Endmills: These are the most commonly available type of cutter. They’re efficient and cheap. Flat Endmills are ideally suited for machining of flat bottom cuts and vertical walls.
Bullnose Endmills: The Bullnose profile cutters are similar to Flat Endmill in that they share a common rectangular side profile but with an additional radius at the bottom corner of the flutes. They are great for quickly removing material while leaving a small bottom radius in pockets.
Side profiles of common milling tools.
Ball Endmill: The Ball Endmill has a full radius at bottom of flutes. These cutters can be utilized for complex surfacing as the contact point between the tool and material surface is constantly changing with variations in the slope of the surface.
Example of Ball End Mill contact point (red) vs centerline of tool (green)
Drills: Drills are used exclusively for making vertical holes in parts. There is no side-to-side or horizontal motion of the tool when using drills. The finished size of the hole will be dictated by the diameter of the tool itself. Besides the diameter of the tool itself, another variable involved with drills is the angle of the drill point. Typical angles are 118° and 135°, generally speaking, the 118° is used for softer materials such as wood or aluminum.
Subsequent operations can be used to alter the size of the hole (reaming, etc.) but those tools are not discussed in this blog post.
Additional Considerations Regarding Endmills: Besides the side profile, it’s also important to understand how the number of cutting edges, or flutes, are formed into the tool as viewed from the cutting end.
More flutes on a cutter restrict the amount of available space for the cut material (chips) to be removed. However, tools with a higher flute count perform better in harder materials.
The cutters shown below are center-cutting. This means that the sharp edge of the flute across the bottom of the mill extends all the way to the centerline of the tool.