How CNC Machines Work

How CNC Machines Work

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cnc machines in a factory

At CNC Estab we have gone over a ton about different manufacturing methods using cnc (computer numerical control), but we still get the occasional message asking us how cnc machines work? Well I’m going to go through and hopefully by the end of this post, you should be able to answer when someone asks you “How does a cnc machine work?”

How a cnc machine works

It all starts with a CAD operator who models the product in 3d or 2d using a CAD program. The most common 2d CAD program would be AutoCAD. I used this a lot in the marine industry for making cut files and nesting parts for cnc cutting. For 3d – there is a wide selections from Pro Engineer to Solidworks to Rhino 3d.

After the file has been modeled in the CAD program it is then exported into a friendly CAM format. For 2d this is typically a .dxf file used by a cnc machine to simulate a path and then cut. For 3d a path is also simulated, but in 3d to calculate how long the machine will take – this also varies depending on the material used (wood, metal, resin etc.)

Rhino 3d to MasterCAM

The CAM program then turns the file from the CAD program into G-Code, which is what the machine will then use to cut/ rout the material to form the 3d product or the 2d cuts in the case of plasma cutting or 2d laser cutting.

So in essence the process is CAD program – CAM program – G Code – Machine does the work.

At each stage there are usually ways to test for success. CAD programs allow checks to see that the 3d object is a closed object. Most competent CAD programmers will export in multiple file formats then try and re-import using the same or different CAD program just to check if it has been exported properly.

Typically large files that do get exported as a .stp or .iges file can sometimes corrupt ot don’t turn out properly. With .iges files I have seen surfaces missing after export – so checking the file by re-importing is very important and a time-saver before handing it off to a cnc programmer or cnc operator.

With CAM programs – these typically simulate the routing cycle. This gives you an idea of how the object will be cut, what paths are used and most importantly, the finish and time something like this will take. The beauty of this is that you will never get a ’round about’ figure from a cnc operator.

The software should tell them EXACTLY how much time a job will take and counting the lead time, you should get an exact estimate on time as well as cost. Don’t be fooled if they tell you otherwise.

Types of cnc machines

There are a good variety of different cnc machines out there. Before going into different mediums, I want to talk about the axis.

3 axis cnc machine

3 axis cnc machine – This means the router only has 3 axis, typically x, y and z. This means the machine can not rout complex shapes. I worked with a cnc operator in the past that had this type of machine, but was able to rotate the work piece in between cuts to achieve close to what a 5 axis cnc machine could do.

5 axis cnc machine – I have discussed these a lot previously here on Essentially you get another 2 axis enabling the machine to rout complex shapes. You will also find 4 axis machines as well.

Mediums – laser, regular, plasma, water-jet. Each is unique and used for different purposes. Check out the respective category pages to learn more. But here’s a quick rundown anyway:

Laser cnc machines – This typically uses a  CO2 laser to cut through the material.

Regular cnc routers/ lathes – This typically uses a cutting edge very similar to a drill piece. Actually many use hardened drill pieces to mill any cnc machine work. Used a lot with foam, wood and for cnc engraving work. Most cnc engraving machines use this regular cnc method.

Plasma cnc machine – Similar to a plasma cutter – A plasma cnc machine is typically used for cutting through steel or metal with extremely high heat.

Waterjet cnc machines – Waterjet machines are awesome. They use a high pressure blast of water to cut through material. They are used a lot in 2d cutting metal/ aluminum. The benefit with waterjet cutters is that there is no heat, so the material does not loose any of its original strength and this process provides an extremely clean cut.

Now you should have an understanding on how a cnc machine works, and what the different kinds of cnc machines are. The cnc process has come a long way in the past 50 years and will only continue to get better and better.

What else do you want to know about cnc machines?

Photo credit: Image 1, Image 2, Image 3


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