The term CNC stands for computer numerical control. Any 2 axis (such as a laser cutter) 3 axis, 6 axis etc. machine can be classified as a CNC Machine. Besides the number of axis, one CNC differs from another depending on what is used as the main cutter. They can come with plasma cutters, water jets, laser diodes, routers, spindles etc.
Our in-house CNC machine is the ‘typical’ Milling Variation, one which has a 3HP variable speed spindle on the ‘Z’ Axis. This allows us to cut through a variety of materials including solid woods, MDF, plywood, aluminium, ABS, and corian.
High density foam for moulds, fiber glass formworks and architectural models
Plywoods, fiber boards and laminate, medium and high density fiber boards (MDF & HDF)
Various sign making materials can be milled with high finish. include more text
Intricate patterns cut-through and scoring for bending.
Solid aluminium at various thicknesses
Milling in solid softwoods and hardwoods
When designing for 3-axis CNC machines there are a few things to keep in mind. First off, your design can be one of 3 types:
Our CNC Machine has a work envelope of 1250mm x 1450mm however most materials such as plywood, mdf, chipboard etc, come in sheet sizes of 2440mm x 1220mm so it is best to keep your design in that envelope.
Depending on the bit being used the vertical workspace is a minimum of 180mm.
When cutting with a CNC, the router bit spins at high speeds and the bigger it is the more force it puts on the material.
If your design has walls or free standing components you need to be sure that it is thick enough to withstand the force of the neighbouring routing.
Depending on the depth/height of the piece and the material being used you may want to keep to a minimum thickness. A Rule of thumb that if it is at least as thick as the router bit it is strong enough to withstand being broken off
It also depends on the material, aluminium will hold up better than wood however some softer materials could actually fair better since not much force is required to cut through them.
Our CNC machine can only mill from the Z axis direction so any design that has undercuts or cavities that would only have access from the side would cause and issue. Also keep in mind that the bit has a length to it and therefore will not be able to reach places that still has material above as it will collide with the spindle. As you can see in the image below, the green section signifies where the router bit has access to, the orange section shows where the bit cannot reach since it is confined to the vertical z axis. Normally the bit would be able to reach the red section at the bottom however in this case it cannot go that far without colliding into the material above it. Because of this depressions that are deeper than the length of the bit cannot have very steep walls.
Tolerances with bits
When designing something to be cut out on a CNC milling machine one must keep in mind the size and shape of the cutting bit. A router bit can come in many variations depending on its use and the material it is designed for.
Two of the most commonly found shapes are end mills, which end up cutting a straight channel through the material, and ball ends, which are spherical at the bottom and cut a curved channel.
Typically for a good finish the ball end will need a smaller step-over than the flat end as it will created ridges as it does parallel runs.
One must also keep in mind the thickness or diameter of the mill bit. Sizes can vary from 3mm to 6mm up to 20mm and more. The most commonly used size is a 6mm or sometimes ¼ inch (6.35mm) diameter.
Since router bit is cylindrical it has a limitation when when cutting inside corners. As you can see in the example below there are two cut outs. The one on the left there is a shape cut out by something like a laser cutter. On the right there is the same object cut out with a 6mm router bit. The differences are that the inside corner of the shape has a 3 mm radius and there is a 6mm offset around the shape that is milled out.
Therefore when designing something to be cut out on the CNC one must keep in mind that any inside corners will have the radius of the bit. When nesting items together the minimum distance from any points on the objects will have to be the diameter of the bit.
Like a laser cutter one may use tabs for a number of reasons.
Tabs may be assigned automatically by the software or designed manually. It is much faster to just let the software decide how many tabs and where to put them however if you design them in yourself you can avoid them being placed in awkward places and put the amount that is necessary.
Please submit your work or design here.