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Last Update: 01-18-2009

Changes may not be apparent but this article is laiden with many links to product pages from many vendors. These pages change from time to time and I make a continuing effort to correct links when appropriate. Products become discontinued or upgraded over time and notations about these changes will appear in the article as time goes by.


Introduction

This project started off when I loaded up a nice freeware pcb layout program (FREEPCB). Many years ago I did PC board work for aerospace companies up until around 1984 when PC CAD systems were just coming into being. Since then I have been computing and wound up owning a couple ISP's and an amusements company dealing with vintage arcade video games. These vintage games brought back memories of my earlier electronics technician jobs in the early 70's.

This prompted me to layout some simple boards like audio amplifiers and converters. These projects were very home brew, breadboard or simple single sided boards, limited quantities. I came across one design however that would need a lot of vias and two layers, and this is where things get going.

Send questions or comments to: wstephen@sowhatsoftware.com

I could of course, send some gerber files to (PCBEXPRESS) or (PCBPRO) online and have them make the PC boards ... IF I WANTED 50!! but I usually only want one or two and I'm a DIY type of person and would rather spend the money giving myself the capability. In order to homebrew two sided plated through circuit boards, I would need to do some good registration, Electroplating copper and in general, make the board the same way the professionals do. In analyzing the pcb fabrication process at (THINK & TINKER) it became clear that before I could electroplate the through holes, I need to have the holes drilled and only after plating could I actually etch the copper patterns. Immediately I knew I first needed a CNC PC Drill.

You can shop around and find a nice one for about $5,000.00 to $10,000.00 which have way more capability than you would need... remember, you're only drilling holes. or... you can find homebrew CNC milling projects online like (THE BRUTE). As I said, I'm very DIY and although the BRUTE plans were available for a few bucks, I decided to take a cursory look at a few hobby machines and set out to design and build my own.

I have a lot a lattitude in the design of this mill because it's really only going to be used to drill holes in circuit boards. It does not have to be real strong and can afford a little sloppiness although not too much. If I make it out of lightweight materials, and keep the axis travel fairly short I should be able to hit these ideals with ease.

Control Electronics - The Motors and Controller

Before we get into the design we need to select the electronics. You can find stepper or servo motors and controllers many places but I found that the package offered by (HOBBY CNC) a good value, and it's a kit too!!! The 3AUPC uses one Allegro Microsystems SLA7062MLF2102 Unipolar Stepper Motor Translator/Drivers for each axis of control simplifying the circuit board considerably.

3AUPC Kit + (3) 80oz-in, 6v, 1.2A, Dual Shaft Steppers


Assembling the 3AUPC was easy and straight forward following the instructions provided with the kit. I have a 40 amp lab power supply which I use to calibrate the board which provides extremely clean DC power. After wiring up the motors to the board terminals and hooking up the power supply, the motor shafts locked in place, just like they should.

Control Electronics - The Power Supply

I do not intend to use this expensive power supply for this project, instead, I will be using an ATX power supply from an old computer. These power supplies have several voltages available but you need to modify it a bit for use as the supply for the stepper motors.



What you do is open up the power supply and remove all the outgoing wires except for a red 5 volt, yellow 12 volt, green enable and two black grounds. Put two 8 ohm 20 watt resistors on the 5V/GND lines mounting them near the fan(large white components in picture) , ground the enable line and run the 12V/GND pair out the grommet to supply the stepper driver. Click here for detailed instructions.

After making these modifications and powering-up the controller board I got the same results as with the lab supply except that I now heard the stepper motors "singing or buzzing". This is probably due to the lower power capacity of the ATX power supply. All that's needed now is 4 holes to mount the case to the machine frame, but let's defer that until we have a frame to use as a pattern. Another nice thing to add is an ON-OFF switch... you know, one of those red button switches that you need to pull on to turn the power on and all you have to do is press the switch to kill the entire system... an emergency stop switch.

Control Electronics - The Computer

Probably the most difficult part of this project so far is getting together the computer to run this thing. This should have been the easiest seeing that I have a few dozen computers at my disposal, but none of them had DOS. I have UNIX, LINUX, OSX, and even an XP or two but no DOS machines. Microsoft does not sell DOS anymore and the software I have chosen, (TURBOCNC) works in DOS. Most of the CNC software runs in DOS... it has something to do with bus timing. I tried an XP machine by making a boot disk as they recommend and I got an "internal error 0222" for my effort, I don't have time for this type of stuff... on to effort #2

I next started off with a SUSE LINUX machine and eventually turned it into a Windows 95 machine setup to boot into DOS mode... that's about as close as I can get to a DOS machine these days. This is not to say that somehow I could have made a pure DOS 6.22 machine or something like that, it's just that I want to get this thing done in some sort of reasonable timeframe. I also want a little "connectivity" on the machine for uploading and downloading data and Windows 95 makes that pretty easy. Of course I would never put this thing directly online because of the highly exploitative nature of such an old operating system. Instead, it will be shared through a Mac.



Control Electronics - The Wiring

Installing and setting-up TURBOCNC was quite easy and I was jogging my motors in no time. I hooked up the limit, home and e-stop switches and gave them a test as well, all seems to work as expected at this point. Below is the wiring diagram for the cnc drilling machine.



Click here to watch the "Jog The Motors" movie (MP3 - 16.50Mb)