CNC Mill

Last updated: 6.4.2003

Intro

After successfully creating a simple, minimal device, cost effective and yet robust circuit to interface a stepper motor using a PC (see Interface), the need to produce the PCB emerged. But having read some tutorials on etching a PCB, the chemicals needed and the disposal issues I started looking for a non standard method. A CNC mill seemed to be the non plus ultra for my needs...

The interface

The interface generally consists of four high current transistors (2N3055) switched by optocouplers to isolate the circuit galvanically from the PC. The diodes (1N4148) prevents the voltage sparks, that are induced when switching a coil of, from damaging the transistors.
[Sorry no scheme available yet]

I currently connect the interface to the pins 2-5 (for the x-axis controller) and the pins 6-9 (for the y-axis controller) of the PC's parallel port.

Note 1: For long term usage small heatsinks may be necessary to cool the transitors
Note 2: Use this circuit on your own risk!

The powersupply

I currently use an old AT PC powersupply. The x and y motors both use the 12V source, the z axis I'm working on runs best at 5V. Remember that an AT powersupply must have a minimum load! If the overall current is less than 1A the powersupply won't work. I used two old harddisks as a dummy load - quite noisy by the way.

The motors

The motor on the x-axis is unipolar AEG stepper I bought some years ago from a local supplier. The y-axis is driven by a stepper I "excavated" from my old deskjet printer. It's also unipolar and works great ;) (no additional information available either).

When assembled the motors make 49/48 steps per mm.

Moving parts

Both carriages are sliding with M8 aluminium pipes (8mm in diameter, that is) on two M6 aluminium pipes. I used a M6 threaded rod glued to the axis of the stepper motor. On the carriages a M6x30 nut transfers the motion. Interestingly there doesn't seem to be a need to use a anti-backslash nut. The x-axis moves amazingly straight. The y-axis however doesn't move that straight because the threaded rod isn't attached centrally on the axis of the stepper motor. But after reglueing the axis should offer an accurancy of 0.1 mm as well, I guess.

Even though the z-axis isn't ready yet and only a pen was used during test runs, the y-axis motor is also capable of moving the much heavier Proxxon (or Dremel if you like). The weight of such a tool even seems to add to the stability of the y-axis' carriage.

The software

The first step is to actually create the PCB's layout. I currently use the freeware linux version of eagle The layout is then converted to hpgl (a simple plotting file standard) using the user program outlines.ulp (see eagle documentation).

Secondly the steppers have to be fed. But as a linux user I found my search for appropriate software in vain. So I rapidly wrote a program that converts a hpgl file into stepper motor commands. It works great for my needs for now, but it isn't ready for publishing yet.

to be continued
: Some unsorted pics :

The base table and the x axis	The y axis
The mill running its first test with a pen (the z axis wasn't ready and the software had some problems)	The mill (without z axis) on my desk
top view on the z axis	Comparing the plotted layout with the printed version (note that the printed version is true to scale)
Engraving an AOL-cd ;)	nice letters ;)
cool spiral engraved on a (AOL-)cd
Dare I try to mill wood? Yes!	hey that's fun ;)

email address: ey enn dee e
thirteen at gee emm ex dot dee e