Building a PCB Mill with Hand Tools
Background
I like building electronic circuits, and have tried various means of producing printed circuit boards (PCB). I have used a laser printer and iron to do the "toner transfer" method. I have drawn the resist by hand. I have etched using ferric chloride and other etchants. I have soldering radios "dead-bug" style and "Manhattan" style.
All of these methods drive me nuts. They're no replacement for a properly made board with properly drilled holes.
Online you will find people using mills to carefully cut out the traces of a circuit board. The bit is then changed, and the mill will drill the holes for the components. Dual sided boards can be made by flipping the board over and milling the opposite side.
This method seems like an excellent solution: repeatable, computer controlled, and chemical free. I've not seen it done, but I imagine a pen could even be set in the mill to draw simple "silk screen" component and connector labels.
The difficulty, of course, is that most people do not have a computer controlled milling machine or access to one. Those that do probably cannot tie it up building boards.
Enter "Tom's Easy to Build Desktop CNC Mill". I saw this video years ago and was always amazed at how easy he makes it look to build one. But I put it off for various reasons until I finally realized I owed it to myself to persue some of the projects I'd long put off.
With nothing but a hacksaw, a battery-powered hand drill, a few random hand tools, a life-time's supply of accumulated electronics crap, and several trips to a local hardware store, I embarked on the path to home CNC milling.
Frame
One thing you'll notice with the video and associated Instructable Tom has put on the web is that there are no measurements or plans. I was going to be buliding this mill completely from pictures.
For the frame, I bought some black pipe from the hardware store.
| Qty | Part | Cost Each |
|---|---|---|
| 1 | 3/4" Tee | $x.xxx |
| 3 | 3/4" Elbow | $x.xxx |
| 2 | 3/4" Caps | $x.xxx |
| 2 | 3" x 3/4" Nipple | $x.xxx |
| 3 | 10" x 3/4" Nipple | $x.xxx |
| 1 | 8" x 3/4" Nipple | $x.xxx |
The frame went together pretty easily. You'll want some way to grab ahold of the pipe. I used some large vice grips and a pair of adjustable pliers. Later I found a proper pipe wrench, which would have worked better.
image of frame goes here
X Axis and Stage Construction
The X axis consists of two pieces of aluminum U channel cut to length and attached across the frame. The tricky part is attaching them to the frame. The black pipe is rediculously hard, so you're not going to get any self tapping screws that I know of to go into there. Even drilling the pilot holes took forever and I broke a drill bit trying to drill pilot holes.
I don't own a tap and die set, so I was amazed to find a tap in my pile of random tools. It was a #6/32, which is a bit small, but I had the right drill to use it so I went with it. I didn't have the handle for the tap, so I just used my locking pliers to hold it and did my best to keep everything straight.
You will need to drill four holes for the U channel.
The next thing is the stepper motor mount. I had picked up some stepper motors someplace for free out of one of the many swap meets held by the DPRG. I used the motors themselves as templates to drill holes for some #6 hardware I bought at the hardware store.
You'll need some 1/4" x 20 all thread for the lead screw. Cut it to length, about even with the end of the U channel. To couple the thread to the motor, try some rubber hose. I used automotive vacuum line that I had in my garage.
The X axis stage was made out of a piece of thick plastic I found in a dumpster behind a place that does CNC machining for injection molds. You could substitute some Plexiglass or other acrylic plastic from the hardware store. I would buy as thick as you can find.
Another piece of U channel is mounted to the stage to act as a guide. You'll need then to fabricate the bearing that holds everything tight. Tom's Youtube video explains this pretty well. I didn't use self tapping drywall screws, but instead used some of the #6 hardware I'd bought. I had the aluminum on hand for some reason, so I didn't have to buy that either.
| Qty | Part | Cost Each |
|---|---|---|
| 1 | U channel | $x.xxx |
| 1 | L extrusion | $x.xxx |
| 1 | 1/8" flat stock | $x.xxx |
| 1 | 1/4" #20 all thread | $x.xxx |
| 1 | automotive vacuum hose | $x.xxx |
| 1 | stepper motor | $x.xxx |
| 1 | #6 washers | $x.xxx |
| 1 | #6/32 nuts and bolts | $x.xxx |