A CNC (Computerized Numerical Control) is a device that can be as small as a desktop computer or as big as a typical bedroom. These machines are programmed from a computer to cut, grind and shape large stocks of wood, metal, foam and plastic and turns said items into something that the user has designed.
I myself has always wanted one. Over the years they have become cheap to build on a small-scale. If I wasn’t living in an apartment and had a real shop area I would build a nice size unit but for now I am going to build a small table top unit that I can use to make PCB’s. If you’re mechanically inclined you can build one out of basic items such as plywood and some metal rods. There are tons of ways to build one. You only need to remember the following factors on what it has to do. You need X, Y and Z. In other words (X) horizontal and (Y) Vertical for the sled and (Z) to control the cutting device to move up and down.
When designing a CNC you want to think about stuff such as the cutting tool, controller board, limit switches, and drive system. Lets go over a few things.
Since my CNC machine is going to be used for cutting printed circuit boards I can use almost anything to build the framework. I plan to do it as simple as possible so I will build it out of wood. Now the whole unit can not be wood. You want some metal parts to the sled can move freely. The sled is the part that moves ether the whole deck of the unit or you can make just the cutting tool move. I plan to make the tool move so the deck can be stationary. Still I need a rail system that is made out of metal. Very simple, you can use metal rods and cut them to length. Now with the metal rods for the rail system I need to figure out a cost-effective way to make them move freely. I could use bearings, bushings or some sort of small wheels. I plan to use some PVC pipe and use it as a type of bushing. It will work just fine with some grease that has graphite mixed in.
Now this can be a head scratcher to some but it’s simple. We want the sled to move but how? Well Stepper motors are used as the drivetrain but how do we make it move. Well you want use a Belt drive system that uses pulleys and a ribbed belt or a threaded rod like a long bolt. I want to cut cost so I want to use a threaded rod. Now there is a draw back. The threaded rod will require the Stepper-motors to make more steps to make a whole rotation. However using a threaded rod will have more torque. Now to use the threaded rod I can’t have it running in the middle of the table sled so I have to use it on ether the left or right side of the deck. This cuts down the cost for a few things however this might be an issue since one Stepper will be used to move the sled. I might have to go back and switch out the bushings to bearings. If I do that I will have to use three bearings in a V shape pattern over the railing. I plan to use three Stepper-motors for this unit. One for each axis. Now I could use four Stepper-motors and use two threaded rods then have the Vertical in parallel and I can cut out the railing. However the threading would have to match and can be a huge headache. Or instead of a threaded rod system I can use a belt drive. For the horizontal Y axis to move the cutting device left and right I basically use the same system as the sled. A single Stepper-motor will be used and a threaded rod system. So once you figure out the main part of the sled the Horizontal will be a cinch. However the Z axis can be tricky. You want a Stepper-motor that can lift and lower the cutting device with out any snags. If you’re using say a dremel it can be easily done. I myself plan to use a brushless motor system and attach a chuck like device so I can switch out cutting bits. Reason why is I want to use a single power source for the device. Once again this will be a threaded rod system.
The items that will cost to most is the stepper-motors. You don’t have to go spend top dollar on the controller board. I plan to build my controller board using basic items and use my trusty 15 year old PC to run it. All you need is a parallel printer port. The controller is easy to build and there are two ways to tackle it. You can use some cheap ICs or a bunch of resistors, NPN transistors and diodes. It all depends on what scale you’re building and how much power your Stepper-motors need.
The IC way
There is a popular chip that is used as a cheap stepper-motor controller called the ULN2003. It’s just a Darlington Transistor array. Works very well from what I can see and I can’t wait to get a few. Now you would need three of these chips, one for each axis. I came across another blog where some fourteen year old built a controller based on the ULN2003.
The long way
You can breadboard this with some jellybean parts so you don’t need a IC. You can even tweak it to use other transistors and such. However this diagram bellow is only one channel and you need four per-Stepper.
I pulled this out of the Datasheet from TI’s ULN2003 IC. I haven’t tried it so it’s up to you. I myself plan to use the IC way of things because you can get the chips dirt cheap compared to all of the transistors, diodes and resistors that are needed. The diagram above is only for one channel and you need four channels per-Stepper.
Stay tuned and follow the build.