Everything you need to know to build your CNC Machine.


CNC is an abbreviation for “computerized numerical control” and means the automation of machine tools by means of computers executing commands and thus controlling movements of the tool and machine.

CNC machines are absolutely mandatory in today's manufacturing processes in almost every industry.
As industrial-scale production of items is hardly ever done by manual/conventional machines anymore the manufacturing process can be completely automated without any need of human labor.
That is to say that CNC machines not only provide much more speed and performance but are also much more accurate than any hand-operated machine. And of course they're able to travel non-straight contours.
CNC controlled machines are most commonly milling machines, lathes, and plasma cutters; however, CNC is also used for gluing, drilling, fabrics cutting and many more.

This page will provide a closer insight into CNC milling machines, CNC gantry routers in particular.

What is a CNC Machine?

Unlike a lathe, a mill doesn’t achieve material removal by rotating the workpiece but by rotating the cutting tool.
This rotating tool is then moving along the workpiece doing the chip removal.

Simple machines provide three axes which enable it to reach every coordinate within the travel range.
Bigger machines often provide a fourth and fifth, rotating axis. These rotary axes allow it to machine overhangs and hardly reachable positions.

Depending on the requirements of stability and speed, a mill can be chosen from Knee-type milling machines, Ram-type machines or Gantry-/Vertical machine centers.

Axes of a CNC Machine
A High-Tech 5-Axis CNC from Deckel Maho Germany

Moving-gantry machines are very common in semi-professional workshops and hobby garages as they offer a lot of travel range on very small operating dimensions and thus fit into small workplaces too.
Relatively stiff gantry constructions have been designed without the use of concrete (UHPC → Ultra high-performance concrete) or tons of steel or cast iron. This makes the gantry construction a perfect model for limited financial resources.

Another advantage of gantry machines is the possibility of increasing the Y-Axis to almost any length.
The only factor limiting it is the ball bearing and linear technology driving the gantry.

However, a negative aspect is that the whole construction gets less rigid when increasing the height of the gantry which is why the travel range of the Z-Axis is limited.

That’s why gantry machines are perfect for milling huge plates and flat parts but not tall applications.

Typical travel ranges for a medium-large sized gantry router are 25” in X by 40” in Y by 6” in Z.

Axes of a CNC Machine
The three Axes of a homebuilt, semi-professional CNC Mill

Basic Parts of a Machine with Moving Gantry

Machine Bed

The machine bed is the base of the machine and where vises or clamping options are mounted.
It is immovable and should be very resistant to bending- and torsional loads which is why it ideally should be braced.

A common machine bed is a frame of aluminum profiles.
This is very suitable because the profiles already have T-Slots where the linear rails can be mounted fairly easy.

The machine bed has linear rails, a ball screw and a motor mounted to carry the gantry.

A machine bed made of heavy 90x90 and light 45x90 Aluminum Profiles
A Machine Bed made of 90x90 and 45x90 Aluminum Profiles


The gantry is the moving part of the machine.

The whole gantry is mounted on linear rails on the machine bed and can move in one axis.

Movement is achieved by:

Linear guidance

Linear guidance is used to absorb transverse forces and guide the block along the guidance.

Profiled rail systems can absorb high forces and keep the construction rigid.

They are also available as preloaded versions.

Preload means that the manufacturer already builds in a tension that is present even when no external forces are taking effect. This prevents any play or backlash between the linear guide and the linear carriage but needs more maintenance and lubrication.

Cheap linear bearings won’t offer enough accuracy and will eventually bend away when high cutting forces are applied.

Ball screws

Ball screws are used to convert rotatory movements to translational motions. They are available with different pitches. Pitches define the ratio between rotations and covered linear distance. Example: A ball screw with a pitch of 5mm will move the ball nut 5mm when performing 1 turn.

Ball screws are normally indicated by the following scheme: Diameter + Pitch A ball screw with a diameter of 16mm and a pitch of 5mm thus will be stated as 1605

Quality determines how precisely the machine will work as a poorly manufactured ball screw could have a pitch of 5.05mm instead of 5.00mm. This will obviously result in an oversized part in the end which is why ball screw accuracies are standardized. (Lead Angle Accuracy)

Accuracy classes are:

Please note: Materials expand or contract with heat differences!

If you don’t have a room that is temperature controlled, it makes no sense to install ≤ C5 graded ball screws!

A ball screw with a length of 1000mm (1m) and a temperature difference of only 10 Kelvin (10°C) will result in an expansion of 0.12mm. That is to say that this is already more than the production tolerance of a C5 graded screw on a length of 300mm (0,23mm < 0.036mm).

Apart from Lead Angle Accuracy another factor that's contributing to inaccuracies is a axial backlash between the actual ball screw and the ball nut.
This causes the ball nut to stand still until the backlash is exceeded, although the ball screw is rotating, resulting in a smaller workpiece than expected.
That's why you'll hardly face a case where your actual workpiece is bigger than intended.

Workpiece Measurement = Programmed Measurement - Backlash

Motor Unit/Spindle

The motor unit or spindle is normally a three-phase electric motor, sometimes having a gear-box in front of it. It is directly connected to the cutter or end-mill and therefore rotating it. While these spindles are often air-cooled in hobby machines, semi-professional and industrial machines normally use water-cooled spindles because their heat dissipation is much better; often, the spindle is quieter as well. A spindle needs a frequency converter which is converting the 50Hz or 60Hz that you get from your socket to the according frequency of your spindle. Increasing the frequency will result in higher rpm’s – and the other way around. The most important criteria for choosing the right spindle are:

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Explosion drawing of the router Technical Drawing of a part
Technical Drawing of a part