On Wed, 13 Nov 2002, Olin Lathrop wrote:

> Back in 1980 I was right out of school and working for HP.  I wanted a way
> to make my own circuit boards for personal projects like you guys are
> talking about.

8< snip...

I used to have an old IBM six-pen plotter (a re-labeled HP 7475, I think,
B size flatbed).  I had excellent luck using a .5mm permanent marker that
I found at an art store.  I had a cut-down HP felt tip plotter pen body
that the new marker friction-fit into.  By setting the plot speed down to
1 or 2 inches per second, I got near perfect boards every time.  I was
only making single sided boards, but I suppose with enough work one could
probably get a double sided board done the same way.

The plotter moved the pen in the X axis and the paper in the Y axis by
means of a rubber lower roller and a grit-faced upper roller.  I did find
I had to tape the PCB to a sheet of paper because the registration process
was at high speed regardless of the plot speed you had set, and the
rollers didn't grip the PCB material well enough to prevent slipping under
that kind of acceleration.

The pen was a common ultra-fine permanent ink pen, available in several
colors from the local art supply joint.  Its only remarkable feature was
that it was small enough in diameter to fit into an HP pen body that had
the top and bottom removed so the pen gripper mechanism could hold onto
it.  I used this setup numerous times with excellent results; the only
reason I didn't mention it long ago is that old HP plotters are kind fo
hard to come by any more.  I think I did mention this on the list a couple
of years ago.

Dale

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