Tuesday, 26 June 2012

CNC drilling challenge

As part of the recent BuildBrighton MIDI workshop, we had to produce about twenty homebrew PCBs. The print and etching part was easy, but what took ages was drilling all the holes for the through-hole components.

There's no doubt that surface mount makes things easy, but when sharing designs and ideas, plenty of people are still firmly in the through-hole camp. So we try to reflect this when making boards for other people to use. Despite having a cnc machine at the 'space, and having access to a second one, the prospect of learning MACH3 and getting all the settings right to drill the holes with the cnc just left us cold. Also, getting everything out, set up, drill the boards, then dismantled and put back away again was going to be a big job (these cnc machines are big beasts and take up a lot of room, so we put them away when not in use!)
We felt it would be quicker for a few of us to just fit a tiny bit into a dremel and go for it by hand.
So this is what we did.

But drilling by hand was a real PITA too, so after this weekend, a few of the BuildBrighton members have set a challenge: To make as small and as cheap a cnc drilling machine as possible.

That description was a bit vague, so we've come up with some "rules":

  • If buying all new components, not more than £50 on the entire build (just think about it, a cnc based device for under £50!)
  • If using salvaged hardware (stepper motors from old printers, for example) not more than £20 total build cost
  • As we're building a small machine, the footprint of the device, when put away, should not exceed A4 size (210x297mm)
  • But it'd be useless if it could only drill tiny pcbs, so it has to be able to drill up to half eurocard sized boards (100x80mm)
  • Any bought components should be accessible to everyone and you should reasonably expect to be able to purchase the same components from the same, or alternative suppliers 12 months from now (so you can't win a job lot of motors from some bloke off ebay and put cost of materials down as 50p)
  • Overseas suppliers can be used to keep costs down, as their price per unit is often much less than UK suppliers.
  • The device is to be platform independent - it can use any microcontroller and any software can be used to control the machine, including homemade software/drivers. 
  • It has only to work on any one platform, not all
  • For accuracy, the drilling machine should be able to drill a 1mm hole in a max-sized 2mm pad and leave a complete copper ring intact around the hole
  • For building materials, assume a price for acrylic sheets as £1 per mm thickness, per A4 sheet
  • Cheaper alternatives (such as mdf or laser ply) can be used instead of acrylic for the chassis if required
  • Trivial components and the cost of pcb etching, running a laser cutter etc and consumables will not be used to calculate total build cost
  • The price for delivery of all components bought online will be included in the final cost

More rules may be added as the build goes on, but only to clarify any points that may arise, not to act as a restrictive force to deter alternative ideas.

So there we have it. Another stupid challenge that probably won't get finished (or much beyond the planning stages) But it always nice to have an excuse to sit around with a brew and kick about a few ideas with like-minded people.

For our build, we're going for cheap AND small.
Most other people have concentrated on one or the other. We're more than willing to sacrifice accuracy for cost, or cost for size, or size for comedy value. As always, sporadic updates, in-between other projects, will get posted here as the build develops.....