Things you should know about
This page is inspired from the years of reading, video-watching of people putting together CNC machines in garages, of seeing them convert an ordinary mill into a CNC capable machine. The post is an attempt to collate all knowledge derived from watching these videos, likely challenges and limitations that one may encounter during such a task. I have absolutely no practical experience in making the machine myself, and have never attempted it, though I think that with access to tools, the task is doable. So, I am an armchair expert at best trying to bring some clarity for beginners and provide an easy introduction to the various ways and possible best choices. So the page is meant for people who know nothing about CNC but are eager to find out ways in which such a thing can be done. The page attempts to cover working details and intricacies associated with various systems and subsystems, choices that exist and various pitfalls etc.
What is a CNC machine?
A CNC machine is any machine that precisely orients work-piece with respect to the tool to perform a desired action. Some of the CNC machines that you can see in market are 3D printer, CNC milling machine, CNC lathe, CNC plasma cutting machine etc. A CNC machine comprises of various subsystems that need to work together to achieve desired result. These subsystems are basically electrical, electronics, mechanics etc. Some of the components of a CNC machine may work at logic level voltage i.e. 5-12 volts while others may require 30-80 DC voltage or single phase / three-phase AC etc.
You can start as small as you wish and can go big as big as to make an industrial machine. For example, a pen plotter is an example of the simplest CNC machine that you can make, while CNC plasma cutting machine, CNC milling machine are a couple of expensive and useful machines, that you can make which can cut metal. I would suggest you to start small and build a comfort level working with the software, electronics etc. before trying to make a large machine.
What about the cost of a CNC machine?
It's hard to say what a CNC machine may cost since there are many variable involved and many choices that you can make. However, what's sure and is common sense is that the cost of the machine will be proportional to the size, so a small machine with less working area will cost less.
Another factor worth considering is the choice of material that you choose to work with. If you wish to make a 3D printer that can print plastic parts, for sure it's cost will be less than for a same size machine that can machine steel. Additive manufacturing technique (3D printing - metal, plastics etc.) is different from subtractive machining techniques (like milling etc.). There are other CNC machines like CNC plasma, CNC EDM, CNC lathe etc. which essentially are similar in principle as far as axis motion is concerned. For the sake of simplicity, we would keep ourselves limited to milling /router machines. Some other factors that can drive the cost significantly upwards is the quality of hardware that you use. So, it's worth considering that you wish to make a machine that would actually deliver results or is some demonstrator piece that just needs to fill project goals in college.
What are the benefits of a CNC machine?
A CNC machine offers great advantage if you compare with any traditional machine of the same type. For example, a traditional milling machine can only cut straight profiles and you cannot move x and y axis so as to generate complex profiles such as a circle, ellipse etc. So, if you convert the same machine to a CNC, the same machine would become more flexible and be able to perform more complex operations.
Who should attempt it?
This a relatively complex question to answer. Nonetheless, I would suggest that you should make an attempt only if you have access to some basic machines that can machine respective materials out of which you wish to make the machine. So equipment like Drill press, Vertical band saw, Welding machine, Lathe, Clamps, etc. may be absolutely necessary. In addition, you should have access and budget for procurement of material metal / wood, motors, electronics, fasteners etc.