[sdiy] Non-chemical PCB production???

[Tim Parkhurst]

Hi Merv, 

It sounds like a fun DIY project, but I see a couple big problems with using
the guts of a pen plotter. 

The first is, as you mentioned, the speed. I think slowing down the clock of
the controller would not do the trick. Depending on how the motor is driven,
there may be some other solution, but I think it would involve some
additional/modified hardware. You might also have a problem if the
controller expects the pen head to move at a certain rate and shuts things
down if it moves too slowly (it might think the head was jammed against
something). 

The second problem would be the torque of the motors that move the pen head.
You'll need a fair amount of torque to move the cutting tool along a path.
Yes, it will be no where near the power required for a milling machine, but
still it will be more than normally needed to move a pen on paper. Even if
the XY motors can successfully move the cutting tool through the PCB copper,
the additional load might cause position errors. Some plotter XY stages have
encoders for position feedback, and some don't (relying instead on a 'home'
signal and then doing relative positioning with motor speed and time
commands from that point). I think it might be fun to try, but if you want
to really get something done, you'll be better off starting with a small
stage meant to do XY movement and using decent sized stepper motors (with
encoder feedback).

Tim Servo (whose first real job was working with SMT pick and place
machines)




> -----Original Message-----
> From: Merv Thomas [mailto:mervynt at mezzie.demon.co.uk]
> Sent: Wednesday, August 27, 2003 12:54 PM
> To: synth-diy at dropmix.xs4all.nl
> Subject: [sdiy] Non-chemical PCB production???
> 
> 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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