Homebrew PCBs

> > andrewm wrote:
> > This is the new thread I have started for details
> > on the laser plotter I am going to try build.

<SNIP>
> Jan wrote:
> The carriage mechanism from an old inkjet or dot
> matrix printer might work for holding the laser
> diode.

Yes, I was thinking printers too.  I have a collection
of old inkys and dottys to pull apart.  Something is
still going to have to be done about the 1000 (or)
2000 dpi resolution requirments though.  Line encoders
seem to max out at a few hundred cycles per inch.

Mechanical multiplication by using a rotary encoder
on the end of a large wheel (like in a mouse) might
work.  But at 2000 dpi I still think that sticktion
may be a big as problem as anything else.  Any one
up for some air-bearings :S 


> I haven't worked with red-sensitive film, have you?
> Green lasers are available for about $60.  That ought
> to work with red-insensitive lithography film (the
> stuff they used in print shops 30 years ago -
> Kodalith?  Even a red laser will expose lithography
> film if you shine it right on the film for a few
> seconds.)

Red film is just easier to get AFAICT.  it's what most
the industry uses so is just more available.  Also
unlike blue-ray DVDs - the red wavelength for photo
plotting is not a disadvantage size wise.  So there
does not seems to be a need for industry to shift.

> Beware of unstable output power as the laser heats
> up:
> http://www.laserglow.com/images/comparearies.gif
> (note, it's not clear whether this is a problem for
> <5mW laser pointers).

I am using a 10mW diode - just because it was available.
It is probably only going to be used at sub milliwatt
levels to get enough light for exposure of an 300mm
x 300mm page in 15 minutes.

I don't think that at sub milliwatt levels heating will
be an issue.  Also the contrast of the film is so step
like that it takes a pretty big change in exposre to
make any change in density.