🚀 go-pugleaf

Adrian Godwin writes:
>I'd like to go one further than David and avoid the need for chemicals 
>altogether : machining the copper surface directly.

We have one of these machines.  It is essentially a precision XY plotter 
with a motor and a chuck to hold the milling bit.  Its XY accuracy astounds
me.  It is on the order of 0.001".

It works by milling away the copper around the traces you want to keep.  
The trouble is that it is tough to make it work reliably.  The mill bit has
about a 90 degree tip.  To make it cut deep enough the minimum cut width is
about 0.010".  When laying out artwork on 0.025" centers that means line
widths are 0.015".  But the copper clad isn't particularly uniform and 
sometimes the mill bit isn't exactly concentric, both meaning your cut width
ends up being greater.  Pretty soon to get cuts that are deep enough across
the entire board the depth of cut (and hence width of cut) gets great enough
to where there is not much left of your traces.

The machine really is nifty to watch in action.  It would be pretty good for
larger geometry layouts.  I would be hard pressed, though, to recommend 
this style milling machine for PC boards with a lot of DIP IC or any other
dense layout requiring thin traces.  Maybe some other cutting technology
would be the answer but I'm not aware of any currently on the market.

Bob

--
Bob Baggerman                         !  bob.baggerman@gtri.gatech.edu
Communications Laboratory             !  bob@comlab.gatech.edu
Georgia Tech Research Institute       !  qseclrb@prism.gatech.edu
Atlanta, GA  30332  USA               !  404-894-3525