3-axis CNC milling device

I've build this 3-axis CNC milling device for milling small mechanic parts. Also, it's capable of engraving and drilling PCB boards. The milling device is a stepper motor controlled x-y table, and a motorized (z-axis) stand for a 'Dremel' tool.

Figure 1: CNC milling machine.

The effective work range is 160*160*65 mm and the mechanical resolution is better than 0.1 mm (stepsize = .02mm).

Mechanics

The device is build of Aluminum strips and profiles. The electronics and power supply are located in the lower part, and the actual x-y table is constructed directly above it. Due to the weight of the power supply the table is quite stable. I'm using bearing reels for guiding the movement in x and y direction. The movement is driven by a screw thread that is kept in place by radial and axial bearings (see figure 2). The Dremel spindle is attached to a part of a Dremel stand. This part is mounted on an aluminum stand, and the lever of the Dremel stand is replaced by a belt-wheel that is driven by a stepper motor (z-axis) (see figure 3). Look at this page for more pictures

Figure 2: The x-y table

Figure 3: The modified Dremel stand with z-axis driver.

Electronics

The machine is controlled by a PC via the parallel port. The electronic part of the device consists of essentially most of the programmer interface described elsewhere, that is driving the output stages of the stepper motor drivers. Each uni-polar stepper motor driver is build of a current controlled PWM power source and some power switches to switch the coil currents. For a change, I did not use dedicated chips to realize the drivers. See the schematics.

Software

The software is running on Windows XP and enables me to directly control the milling machine, and to execute a Gerber 274 file. Since the same electronic interface as the programmer was used, I could happily copy the low level driving code and drivers. The maximum stepping speed seems to be limited to about 500 steps/second. Since I did not implement acceleration, the stepping speed is limited to 250 steps/second.