A while back we started looking at the feasibility of manufacturing at home. The reasons are many, but that’s a discussion for another day. So far, we’ve been looking at how to screen print double-sided pcbs before immersing in ferric chloride for etching.
Now double-sided boards mean finding a way of lining up the prints on both sides of a board. And the most obvious way to do this is to pre-drill the boards before printing. Which in turn means using a CNC machine.
We built a CNC drilling machine for under £50 last year which was pretty accurate – up to about 0.5mm which still made for some pretty useable PCBs. One idea (which we’re not dismissing – just haven’t time to implement just yet) is to add a camera to the drill head and drill a pre-printed (but not-yet-etched) board. The drill head can move into position, then we use the image from the camera to ensure the drill goes exactly into the centre of each hole by jogging the x/y axis a little until perfectly lined up. This should at least remove the 0.5mm inaccuracies we got during testing. With one side printed and the board drilled, we could then line up the board and print the second side before etching the entire thing.
But just right at this minute, we’ve not really got time to do more development – especially not when we’ve a 0.1mm accurate CNC milling machine gathering dust under a table somewhere….
It’s been a few years since this thing was fired up, and it was supplied with RoutoutCNC software (incidentally, this is now being given away with free licences since it’s no longer supported) but we couldn’t get it to work properly. Each time the x-axis moved, the z-axis travelled downwards about once every 10 steps.
Mach3, however, worked just fine (once we’d spent a few hours setting it up and replacing the 25-pin serial cable we thought was a parallel one with a proper, straight-through parallel cable). Here’s the CNC in jog mode.
The CNC machine has been made for milling. It’s a sturdy, chunky beast and uses really good quality lead screws on each axis. So it’s pretty accurate and has very good repeatability. The only thing is – it’s so sloooowww.
It’ll have to do for now. Maybe hacking our own mini drill machine in future isn’t such a bad idea after all!