In the summer of 2012 I finally made the move and bought myself a tiny hobby CNC machine after years of having wanted one. Being in school at the time my financial resources were fairly limited, but I managed to scrounge enough cash to pick up a used kit machine off of Craigslist in Vancouver for around $350. Though the machine is quite small and therefore limited in what it can be used to make, it has paid for itself many times over when I consider how much I have learned about the CAD/CAM process and CNC machining in general. The biggest misconception many people have is that CNC manufacturing involves nothing more than drawing something in AutoCAD and clicking "File --> Send to Mill". The CAM ("Computer-Aided Manufacturing") process is an entire process on it's own that requires careful planning to produce manufacturing data that will get the part made quickly and efficiently.
Zen Toolworks CNC Router Inside the Custom Cabinet I built for it (Click to enlarge)
The machine itself is a three-axis gantry-style router with an E240 DC spindle motor. The three axis motors are wired up to parallel-port motion control board (shown below) based on a popular stepper motor driver IC, the name of which escapes me at the moment. The motion control card is driven from a CNC controller program called "Mach3" running on the PC sitting to the right of the CNC cabinet. Mach3 takes "G-Code" files generated by CAM software (I use CAMBam) and translates them into actual XYZ movements to send to the motors on the machine.
No-Name Three-Axis Parallel Port Motion Control Board (Click to enlarge)
At the moment I have a very crude spindle motor controller rigged up which I plan to replace with something a bit more professional in early 2013. The E240 spindle motor that came with the mill can run from 0-9000 RPM with a power supply ranging from 24-110VDC. Unfortunately, finding an affordable power supply that can deliver several hundred milliamps is more difficult than one might expect. My interim solution was to daisy-chain several laptop AC adapters together to wind up with roughly 100VDC, which is then fed in to an LM555-based PWM motor speed controller, the schematic for which is shown below. This is a terribly hokey solution, however I must say it has held up surprisingly well over the time it has been in service. Regardless, if you are planning on building your own spindle motor controller please don't do what I've done - buy a real power supply!
Crude LM555-Based PWM Spindle Motor Controller (click to enlarge)
Over the Christmas holidays I have been putting the finishing touches on a design for an all-in-one power supply and speed controller that I hope to build early in the new year. Despite it's simplicity, the LM555-based circuit above did an excellent job controlling the speed of the spindle motor over a fairly wide range. While it does a fine job, it has two main deficiencies: The first shortfall is that the spindle motor controller is in no way linked to Mach3, meaning that both the spindle motor power and speed must be set manually. The second problem with it is that it is a completely open-loop system, meaning that the controller has no idea how fast the spindle is actually
turning. I have rigged up an optical encoder on the spindle so the speed can be measured on an oscilloscope, however it would obviously be much nicer to have controller and spindle operate as a closed-loop system with the speed setpoint and value accessible directly from Mach3.
Complete CNC Setup (click to enlarge)
Like many, this is an ongoing project that I hope to write more about as I have the time. Above is a photo of the complete (current) setup. The mill is housed inside a particle-board box I made to keep the noise and dust confined, as the machine lives in my kitchen (the joys of living in an apartment). The PC to the right runs Mach3 (the controller software) on Windows XP, so I can create my CAM toolpaths on my regular computer and just download them to the mill as opposed to creating the CAM data on the machine. The large ball of wiring to the right includes power supplies for the spindle motor and motion controller card, which is mounted on the back of the plywood box. Two halogen lights on the ceiling of the box make it easy to set up workpieces in the machine. A row of hard drive magnets is mounted on the door (left) to serve as a convenient tool rack from spindle and clamping wrenches.
That's all for now - more details to follow! If you have any questions please feel free to shoot me an email via the "Contact" tab!