In article , rickman wrote:
On 5/27/2015 7:29 AM, gareth wrote:

I wonder if anyone here has experience of milling PCBs using
CNC rather than etching them, and if so, what pitfalls and pratfalls
were encountered?

Years ago a place I worked had one of the machines that cost a few
thousand. It wasn't great as they hadn't provided a good base so the
board could be inserted multiple times with the same registration or
easily flipped for double sided. The bits were conical rather than flat
tipped and tended to break easily. In the end the company went belly up
and we were stuck with proprietary software that was no longer
maintained. The only people who really used it much were the RF guys...


There are still fast-prototyping PCB milling machines which do this.
They don't seem to have a really big market - "quick turn" fabrication
houses are plentiful and are usually quick enough. In-house milling
seems to be mostly for "We've gotta have this *today*" applications,
or for the occasional situation where one is too afraid of having the
details of the PCB "leak" to a competitor before the product comes
out.

From what I've heard, one of the problems with this approach is that
milling the copper off of the PCB isn't a trivial problem. Copper is
soft and flexible enough that it can tend to clog the bit, or
stretch-and-tear rather than milling off of the substrate cleanly.

Some hobbyists do it with (e.g.) Zen CNC systems, or Dremel-based
CNCs, etc. I know there's software out there which can read in a
Gerber file, and produce a file of G-code commands which will mill out
an isolation zone around each trace or area plotted by the Gerber. As
with an etched PCB, you'd want to fill as much as possible of the
unused space with ground plane (or unconnected fill zones) so that you
don't end up having to mill away lots of copper.

Using carbide bits would (I think) be essential - high-speed steel
probably won't stand up to FR4 for very long.