On 27.5.2015 14:29, 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?


I have experimented some pcb milling, using desktop CNC with
working area slighly larger than A4-paper. Smallest SMD
components were 0603 size, using v-shaped engraving bits of
0.1mm tip diameter.

Needs two softwares, first one to design the pcb and second
phase is to convert this to cnc code. This takes some time
as the cutting procedures are adjustable to each line on pcb
desing.
The need to adjust hole sizes, viases, layers, line widths
depend on pcb, more complex designs take more time also
preparing time for cut and transfer to individual cutting
files with different tools used. Some re-design is needed
sometimes between pcb-design and cnc-prepare as cutting
width is constant.

This two-phase is one way to do all, some sw packages do
both phases internally and the pcb design is directly what
is actually cut, this may sometimes be less optimized for
cutting time spend.
So software selections need some evaluation depending
on the actual needs.

Third sw is needed to finally control the cnc-cut described
in the tool path files prepared in two previous phases.

Most difficulties are keeping pcb material exactly flat on
milling base plate, use of vacuum plates might benefit, but
this needs extra accessories like vacuum pump etc. so this
isn't choice for occasional use.

CNC machines are like cars, some of them have automatic tool
changers, some don't, some automation speeds much the
time spent on tool changing between cuts, though by
increased price level of the cnc-mill.

CNC is ok for prototyping or limited small amount of pcb's,
as pcb markings and specific solder layers are not simple to
add to milled plate.
Commercial processing is done using more sophisticated means
and machinery so all these comments don't apply to them.

To sum briefly, most of the time around 50..70% of time is
spent on describing pcb-files and preparing them to cnc code.
Actual cut is 10...20% of time used.