Some updates since the last time.
After a few attempts to draw an outline PCB, I realized the system was skipping steps - that is not good! I was using type 9 stepping (1/2 step wave drive, 1000, 1100, 0100, etc). I thought maybe this was too fast, so I changed to type 5 - full stepping. The pattern is a single coil at a time (1000, 0100, 0010, 0001). This didn't help. The key was wave driving, type 6, which has 2 coils energized (1100, 0110, 0011, 1001). This cleaned up the stepping, and with a fine tip Sharpie, I was able to draw this PCB! The board was designed in Eagle and the g-code produced by pcb-gcode.
Actually milling the board is still a challenge. Bits are breaking, router is wiggling on the weak bridge, etc. Once my bearings arrive, the plan is to overhaul the bridge.
Upgraded driver - Sparkfun had a free day back in January. I managed to score $20, and so I ordered an EasyDriver. This has replaced the rats nest that drove the Z-Axis and free'd up 2 control lines for future considerations.
I also learned how boost the speed by nearly 100%. Thanks to a friend who knows way more than I do about electronics, I increased the driver voltage from 5V to 12V. I had to add current limiting resistors in line to protect the motor. A pair of 15 ohm, 5 Watt resistors per coil did the trick. They run quite hot, so some heatsink will probably be in order. But still I'm happy for the speed! I can now run the X & Y axis at 13" / min on 1/4" 20TPI rod.
To help with troubleshooting, especially when we rebuild the bridge, I am working on a test controller. A 555 generates pulses into a PIC which puts out the full step wave driver pattern. This will be sent to the driver circuits when the machine is away from the host PC getting rebuilt.
And finally, a big power upgrade. The little rotary tool I'm currently using is pretty limited in the bits it can handle. This week Canadian Tire had their 'Spin Saw' on sale for $69.99 (regular $139.99 - 50% off!). I could not resist. This thing has power. Over 5A of power. 30,000RPM of power. 1/8" or 1/4" collets means I can put the little finishing bits for PCB work, or bigger milling bits for more manly jobs. (insert Tim Allen laugh here).
Till next time!