[sdiy] Non-chemical PCB production???

[Tim Ressel]

Merv and all,

Since I have experience with LPKF products and HP
products, I thought I should break radio silence and
toss a couple of pennies in...

The LPKF goes pretty fasy then cutting traces. But
when cutting board outlines it slows way down. So a
variable speed drive would be nice. I am concerned
about the motor being too heavy for the 7475's
carriage to hold. If thing is going to drill holes
then there will be upward force on the carriage,
something it was not designed to handle.

Another issue that has to be addressed is the setting
of the working height of the cutting tool. LPKF does
this with a threaded adjustment collar on the cutting
head. Their competitor (name?) does it by adjusting
the cutting bit with feeler gauges. The LPKF method
requires cutters with precise overall length so that
only one adjstment is needed. Both mashines have a
'nub' that rides on the surface of the PCB and serves
as the reference plane for height.

Hope that helps.

--tr

--- Merv Thomas <mervynt at mezzie.demon.co.uk> wrote:
> 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
> 


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