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CNC Explained

When designing your CNC project there are many variables to take into account. From the thickness & properties of a given material through to the way in which you design part intersections and approaches to fastening. There are lots of things to plan for. Don't worry if you aren't familiar with all the intricacies of CNC based design- we are and we are here to help you.

This section of our site is designed to give you a basic understanding of some of the principle techniques involved in producing your projects using CNC strategies.

General considerations

Layout of parts

When planning the layout of your CNC project please remember that the arrangement of the parts to be cut needs to allow for retaining sections. If we look at the diagrams below we can see that one of the layouts has a uniformly spaced approach and the other has components which are positioned butting together. The first approach is acceptable the second will not process correctly. Without retaining sections the parts will move during cutting- this results in inaccurate results.

Toolpath consideration

When cutting with a CNC tool we need to take into account the diameter of the cutting bit. For example. If we are cutting parts with an 6.35mm diameter bit we need to remember that the tool will leave a hole in the substrate 6.35mm larger all the way around.

When planning the layout of parts it important to allow for the additional space that each toolpath will occupy.

Processing thicker materials

Cutting bits are the key to any CNC system. Use the right bit for the right material and you will get excellent results.

From our experience a lot of signage and display work requires the use of a fairly fine bit. The general rule of thumb for cutting bits is that they will cut to a maximum depth which is no greater than 200% of the bit diameter.

The obvious approach for thicker material would be to use a larger diameter cutting bit. The problem with this is that tight shapes such as lettering won't cut accurately with a larger cutting bit as there will not be room for the bit to move through the material without it destroying areas we want to keep.

So how do we cut thick materials with a fine bit?

The process we employ to get around this problem is referred to as "passing". We tell the machine how deep we want the cutting bit to penetrate- for example if we are cutting 18mm thick material with a 3.95mm bit we might say cut only 6mm deep in any one action or "pass". The software will then interpret this data and instruct the CNC machinery accordingly.

So, in this example the CNC will cut round the perimeter of our part three times in negative 6mm increments- the final "pass" cutting through the last 6mm deep section of our 18mm sheet.

Area clearing/ Pocket machining

Area clearing or pocket machining as it's sometimes referred to is the process whereby an area is cut to a specified shape and depth in one operation. Again, this is an automated feature of our CNC systems and is a vital tool for creating many CNC projects.

How the process works

Area clearing/ pocket machining employs both perimeter toolpathing and elements of passing. As an example lets say we want to machine a recess into an 12mm sheet of MDF. We are going to form a basic trenched joint. For this we need to assign an area clearing strategy to a rectangle which is 12mm wide by the length of the panels we are going to join.

This rectangle is assigned a clearance tool path which will cut around the inside of our 12mm rectangle using a 3.95mm bit- if we were to ask the machine to go to the outside of the rectangle it would area clear an area 12mm +3.95mm +3.95mm- the two extra dimensions represent the diameter or the tool as it travels along the outside of the perimeter- this refers directly to the toolpath strategies we covered earlier.

Using this area clear method we can ensure that we get recesses which are precisely the shape & dimension we want and which also have a specific, uniform depth.