MFW June 2013 - Page 7

Before I say anything at all, I have to make it very clear that “I am no expert at CNC”, but I do have quite an interest for it and have managed to get some very rewarding results out of the many hours I have put into it. My interest started about 15 years ago after seeing a kitset CNC router unit from a company called Step four in Europe. I’m not sure if they even exist anymore, but it did get my attention towards building my own. For quite a few years I have been playing around with stepper motors out of old printers and trying to get some sense out of them with little success, but more recently this has turned around. So over the next couple of editions of Model Flyers World I will share with you what little I know of it. So, what is CNC? CNC, or Computer Numerical Control is where you can take control of a machine such as a mill, router, laser cutter, plasma cutter, lathe etc. and drive the multiple axis of these machines to very accurate tolerances by computer commands. Additionally these actions can be repeated multiple times to obtain perfect repetitious quality of the parts you choose to make multiples of. Some of the larger, more complex (and expensive) commercial milling machines are operating 6 axis control of the cutter head, giving them basically infinite access for those intricate jobs. The compressor wheel in my Jetcat turbine engine is machined from a solid piece of aluminium by one of these six axis machines and can be seen in this You Tube video clip: http://youtu.be/5Vojok45Q-c But the more simple router machine I have built controls the three basic X, Y and Z axis, which I find more than adequate for what I need to do. More about this later. Where does it all start? The CNC machine, like most computers, is quite dumb until you as the operator give it the commands of what you want it to do. To do this we use a CAD (computer aided drawing) or CAM (computer aided manufacturing) program on any desktop or laptop computer to draw the component we wish to make. The level of drawing is really only limited by your imagination and most probably quite a few of you have already had some hands on experience playing around with CAD drawing programs of some sort. However, unlike a lot of CAD programs out there, this program also needs to have the added ability to generate a specific code called “G Code”. It is this code we then put into the CNC machine to give it the commands of operation. If I have now sparked your attention, you can download a free version of a CAD/CAM program called CAM BAM, which also generates G code. When I say free, I really mean you can use it for 40 times before you have to pay for it to do any reasonable size job, but this will give you a taste of it with plenty of time to decide if you want to go further with it or not. It also has a few very good video tutorials to view before you download it, to see if it is right for you. Have a look at: http://www.cambam.info/. There are many similar programs out there to use, but I have found this one to be pretty straight forward for getting Top: Router table computer terminal Middle: 1300mm X 900mm Router Table Above: The brains of the table. Upper right corner is the 48 volt power supply with the 5 V plug pack in the power point below. The clear plastic box on the left provides ventilation to cool the 4 stepper motor drivers and has the breakout board mounted on top of it in the lower left corner.