[sdiy] Non-chemical PCB production???

[Merv Thomas]

Hey Obe-Wans,

Here's a DIY (not synth specific) question for you concerning the
non-chemical production of small PCBs. As far as I can tell, the only
non-chemical method of producing PCBs is to mill contours around traces and
lands - I'm sure you've all seen the LKPF, or is it LPKF? - I can never
remember. It produces nice looking little boards in a reasonable time, but
it costs a small fortune. So I got to thinking . . . hmmm, could I get
something close to this using alternative means.

Over last weekend, a swoop on a local car boot sale resulted in me now being
the proud owner of an HP7475A pen plotter. You know this puppy is sitting
there and I'm wondering could this thing be converted into a weapon of board
construction?

As a plotter it moves the paper in the Y direction (front to back) while the
pen moves along the X axis (side to side). The stepper motors are beefy
enough to move the couple of ounces a piece of copper clad would weigh, the
accuracy is good enough for home brew but I'm not sure how I would make the
cutting 'head' to sit in place of a pen . . . I would guess at some sort of
little pin chuck and a small, high speed motor arrangement but that's where
my engineering knowledge leaves the building.

Anyone ever seen/done anything like this before? Problems I can see: the
speed of the thing . . . it'd need to be slowed down some to cut rather than
draw. I had a look at the controller board - ain't it wierd, the first thing
you do to a new piece of kit is take it to bits to see what you got :)  The
controller is a 4MHz 6802 based thing . . . changing the crystal would slow
it down maybe? There's probably a means of slowing it down programmatically
too but I've no manual. Another problem is the lack of Z axis control - the
HPGL it uses as a control language has pen up/pen down and that's it. The
actuator that moves the pen up and down is a rather crude affair - a lever
on the end of a solenoid - but it works.

If there are any engineers out there who could make suggestions, I'd be
grateful.




Happy trails . . .



Merv