cnc could be so much fun, if it wasn’t so difficult for the common artist and designer to access and learn this ancient but amazing technology.
Let’s face it: CNC prototyping usually isn’t meant to be tackled by artists and designers. It’s an industrial technology mostly used in settings where sizeable budgets are in play and trained professionals work together according to pretty tight specifications. Especially with metals, CNC is more science than craft and one better exactly know what one is doing or else risk break materials, tools and worst case risk the machines themselves or injury. Being an artist and designer myself i have suffered many years through the frustration of trying to find some prototyping facilities who are willing and able to work with me on artistic projects and get my ideas from my brain into my hands. Most of the times CNC operators already cringe when they hear the wort art uttered in the same sentence with CNC, and probably understandably so since most of the times not only are the budgets artists usually have ridiculously small compared to industrial projects but artists rarely have the experience required to provide CNC shops with accurate briefings and source files. Now of course most smaller CNC-shops will happily let you try and fail a couple of times and help you reach the desired result eventually but this usually comes with a hefty price-tag and i have rarely found a prototyping facility where keeping the cost low by improvising has even been an option.
In the following i will try to give a very high-level explanation of a couple of topics one should keep in mind when approaching CNC.
What is CNC ?
CNC stands for Computer Numerical Control and according to wikipedia Numerical control (NC) is the automation of machine tools that are operated by precisely programmed commands encoded on a storage medium, as opposed to controlled manually via hand wheels or levers, or mechanically automated via cams alone. Most NC today is computer numerical control (CNC), in which computers play an integral part of the control.
When people talk about CNC, most of the times they mean some kind of computer controlled milling machine, or in other words an automated (computer controlled) router. I think of CNC in a more broad definition since strictly speaking 3D printers, laser, plasma and waterjet cutters, knitting, embroidering or weaving machines and many other interesting production tools are also under computer numerical control. Regardless of semantics however this all boils down to creating things from raw materials with a machine from files generated on a computer and until the tool hits the material there are many similarities in workflow and process, all requiring in depth knowledge and experience of 2D and 3D software and file formats.
What are the limitations and pitfalls of CNC ?
When working with a 3D modeling software in the virtual realm one quickly forgets that the real world has such annoying constraints like gravity, friction and statics. So for example it may come as a surprise that a rod with 1mm diameter does not fit into a whole of 1mm. Or that you can’t make a square hole or pocket with sharp angled corners. But these are just minor annoyances that rarely compromise a design on the whole. Ive found that for most projects the most significant limit is size. Imagine cutting a hula-hoop ring with a CNC-mill out of a solid block of wood. Since milling is a subtractive process here would be 99% percent waste so i think it’s fair to assume nobody ever attempted to do this(although you could cut out the center first and use it as a dining table top). 3d printing however is an additive process so this should work, but trying to upload a model of this to a low cost printshop like shapeways quickly reveals that objects that large can’t be printed at all or only at a ridiculously high price. On the other hand of the scale, when you’re trying to make tiny objects both milling and 3d printing are quite tricky. On a CNC- mill the limit is the size of the tools available (they are called ‘bits’), with the smallest diameter being around half a milimeter. In most affordable 3D printing systems there is an error margin of up to a milimeter and a minimum ‘wall thickness’ of around a milimeter required. This limits the amount of detail one can create and with milling also the speed at which you can work. Small router-bits are pretty fragile and break as easily as a tooth pick … so with tiny objects the machine needs to advance quite slowly, increasing time and cost. Sometimes, as appealing as the concept might always sound, CNC is not necessarily the one-size-fits-all solution and maybe a combination with other processes or techniques is required.