Homebrew PCBs

--- In Homebrew_PCBs@yahoogroups.com, roger lucas <ralucas4277@y...> 
wrote:

>>SNIP<<

> Andrew,
> 
> The pcb must be edm'ed in a raster fashion, ie
> consecutive passes with the electrode so that the
> electrode always approaches fresh copper, analagous to
> the old dot matrix printers.
> 
> However, I have no knowledge of an off the shelf
> package to convert pcb layout to raster scan format.
> At the moment I am converting to bitmap and cobbling
> from there. The resulting file needs to be edited for
> spark on/off to pass over copper that has to remain.
> Maybe someone can help here, by suggesting a better
> process!
> 
> For further enlightenment see the following messages
> on the Homebrew_PCB forum,
> 
> 9593, 9594, 9602, 9604, 9614, 9805, 10006, 10024,
> 10096, 
> 
> I am interested in the dielectric fluid you mention,
> and will try to obtain some for trials.
> 
> Roger
> 
>

Roger,

If you were to make your scanning system move both the EDM mechanism 
and an opto head looking at a conventional translucent PCB image, the 
digital signal from the opto sensor could turn off/on the spark 
source and there would be no need for custom software ! The original 
Muirhead wet fax machines used a similar set up with a light sensor 
looking at the source document, it's output sent down 'phone lines to 
a receiver where 'almost'point contact between a fixed horizontal 
blade, and a rotating helical blade (like a cylinder lawn mower) 
passed electricity though a paper soaked in an iodine compound to 
make the mark.

I'm afraid  the dielectric was rather expensive - particularly as I 
needed 19 gallons (!!!) In fact I seem to remember paying almost as 
much for the fluid as I did for the (none working at the time) EDM 
machine <G>