🚀 go-pugleaf

In article <18219@acorn.co.uk> agodwin@acorn.co.uk (Adrian Godwin) writes:

<about making PC boards>
>I'd like to go one further than David and avoid the need for chemicals 
>altogether : machining the copper surface directly. The cutter would have
>to be extremely small to do a useful job, but perhaps some sort of spark
>erosion system might do it.

	Spark cutters (electrical-discharge machining tools, EDM)
are probably not the best way to do this.  In principle, one makes a
fast spark and blasts out material with a combination of heat and
ionization (the + ions that result from metal eroding are usually
repelled from the workpiece, which is a positive electrode), with a 
bit of acoustic 'blast' effect.  EDM works well on brittle or
nonrefractory metals, or on materials with a low thermal conductivity.
There is a minimum of electrical conductivity, below which 
EDM is ineffective.

	Removing a thin layer of copper runs into two problems: first,
the EDM machine will have to follow the plane of the copper board very
well (a few thousandths of an inch is enough to change the spark).
Second, the EDM has to be well-connected (electrically) to the parts it is
cutting out.  You'd have a hard time making it work with a 
plotter-style 'cut list', because a section of the copper could 
become electrically isolated during cutting.  Better would be to 
raster-scan the PC board, which requires some conversion software
(and a bit-map picture of the board to be created, with fine detail...).

	You could just sandblast, of course.  It might be possible to
do the drilling at the same time as the etching (saving those pesky
little extra steps...).


	John Whitmore