CNC milling at Maxton Design – precision machining of parts

CNC stands for Computer Numerical Control. A CNC milling machine is a machine in which a rotating tool – the cutter – removes material layer by layer, following a path planned on a computer. That path is based on a 3D model, so the machine reproduces the design with an accuracy that can’t be achieved by hand.

The biggest advantage of CNC is repeatability. Once a program has been perfected, the machine carries out the same operation identically on the first piece and the thousandth. When making parts that have to fit the bodywork to the millimetre, that’s essential.

It all starts with a 3D scan of a real car. Based on this, the designer creates a digital model of the part, and then a program is prepared for the machine – the paths the tool will follow. It’s this program that determines how precisely a mould or the outline of a finished part is cut.

The program isn’t final from the first attempt, though. Before series production starts, the first prototype set is fitted to the very car that was scanned earlier. If our fitters notice that anything isn’t sitting perfectly, we correct the mould or the cutting program. Only the perfected program goes into series production.

The machine’s first job is to mill the mould on which the ABS parts will later be formed. The CNC machine cuts it straight from the 3D design, and a single mould takes around 24 hours of continuous machine time. That long time comes down to precision: the tool passes over the mould’s surface many times, reproducing every crease, curve and edge.

After milling, our team smooths the mould by hand. The mould works like a stamp – any imperfection left on it would show up on every part made from it. We describe what happens next with the mould in our article “Thermoforming: how a flat sheet becomes a splitter”.

After thermoforming, the ABS part is still part of a larger sheet, with excess plastic around the finished shape. Now the part has to be cut out of the sheet so that its outline matches the design exactly. This is the stage that determines whether the splitter’s edge will be perfectly straight and whether the part will sit against the bumper along its entire length.

This is where CNC repeatability really pays off: an outline cut using a perfected program is the same on every piece in the series. That means two splitters for the same car model, ordered several months apart, will look and fit identically.

The Street Pro line is made differently from our classic ABS parts. Instead of being thermoformed, the parts are cut on CNC milling machines directly from a thick ABS sheet. It’s a material with increased impact and scratch resistance, in matte black, which doesn’t need painting.

A thicker sheet means a more solid, stiffer part – which is why Street Pro is a good choice for cars that often run low or drive on poorer roads. From a production point of view, it’s also a different challenge: the machine has to cut through much more material while keeping the edges clean and straight.

CNC milling machines also work in our carbon division. They mill the working moulds from which the carbon production moulds are made. The requirements here are even higher – working moulds are milled for several days, and in some cases more than ten. Any imperfection would be carried over to the carbon mould and then to every part that comes out of it. We describe the whole process in our article “Carbon – how we make carbon fibre parts”.

A CNC machine is precise and tireless, but it has no eye. After machining, every part goes into the hands of our team. They sand the edges, remove small burrs, give the part the right outline, thickness and look, and finally polish the surface.

This combination is the foundation of our production: the machine provides accuracy and repeatability, and people provide a finish that can’t be programmed. Before a part goes into the box, it also goes through quality control. Only then do we know that a flawless product is on its way to the customer.

For you, CNC milling means one thing above all: predictability. The part you order has exactly the same shape as the prototype fitted to a real car. The edges are straight, the outline follows the bumper line and the mounting points are where they should be. That translates into easier fitting and a result that looks factory-made.

It’s also one of the main differences between Maxton Design parts and cheap replicas, which are often cut by hand or copied from someone else’s product. You can read more about these differences in our article “How Maxton Design splitters are made”.

What is CNC milling?

It’s a machining process in which a computer-controlled machine removes material with a rotating tool, following a path planned from a 3D model. It provides high accuracy and repeatability.

What does Maxton Design use CNC milling machines for?

For milling moulds for ABS parts and working moulds for carbon parts, machining parts after thermoforming, and cutting Street Pro parts directly from a thick ABS sheet.

How long does it take to mill a mould?

A mould for ABS parts takes around 24 hours of machine time. Working moulds for carbon take anywhere from several days to more than ten.

How does Street Pro differ from standard ABS parts?

Street Pro parts are cut on CNC machines from a thick ABS sheet with increased impact and scratch resistance, instead of being thermoformed. They have a matte black finish that doesn’t need painting.

Are parts ready to fit straight after CNC milling?

Not straight away. After CNC machining, every part is sanded and polished by hand and then goes through quality control.