Homebrew_PCBs

Hello group,
Has anyone here thought about building or even built a drum
photoplotter based on a red LED laser diode ? This would be used for
making printing masks, et. There has been much discussion among amateurs
on building a CNC mill/drill machines, however I am under the impression
that this is definitely NOT an task for the beginner, even if he/she
has access the right tools. A drum photoplotter appears simpler in
construction as there is only 1 axis required to position the light
head. Basically the drum plotter works by rotating a relatively large
drum with a film sensitive to red light (available from Kodak)
positioned around the outside of the drum. The drum spins at fairly high
speed (> 10 rev/sec) and the light source (red LED laser diode and
focusing lens) slowly and accurately moves along the length of the drum
in a straight line. The spinning drum sounds relatively simple to build.
The moving light source looks a lot more complicated / expensive. My
only thoughts how to go about this is to use a ball bearing screw and
linear bearing. I priced some ready to go ball screw guided assemblies
but the costs were prohibitive. Is there no other option ? I own a drill
press and a small lathe in my workshop. I am open to all comments.

Hi,

> speed (> 10 rev/sec) and the light source (red LED laser diode and

Usually cheap laser diodes are very bad source for points. The light
spreads unevenly and in a weird pattern. The optics to make it a point
source would probably end up being more expensive than using another laser
source.

Best regards,
Alexandre Guimaraes

Adam Seychell wrote:

>
> Hello group,
> Has anyone here thought about building or even built a drum
> photoplotter based on a red LED laser diode ? This would be used for
> making printing masks, et. There has been much discussion among amateurs
> on building a CNC mill/drill machines, however I am under the impression
> that this is definitely NOT an task for the beginner, even if he/she
> has access the right tools. A drum photoplotter appears simpler in
> construction as there is only 1 axis required to position the light
> head. Basically the drum plotter works by rotating a relatively large
> drum with a film sensitive to red light (available from Kodak)
> positioned around the outside of the drum. The drum spins at fairly high
> speed (> 10 rev/sec) and the light source (red LED laser diode and
> focusing lens) slowly and accurately moves along the length of the drum
> in a straight line. The spinning drum sounds relatively simple to build.
> The moving light source looks a lot more complicated / expensive. My
> only thoughts how to go about this is to use a ball bearing screw and
> linear bearing. I priced some ready to go ball screw guided assemblies
> but the costs were prohibitive. Is there no other option ? I own a drill
> press and a small lathe in my workshop. I am open to all comments.

I've thought of doing it, but my epson is good enough for the moment.
It's currently used for some high resolution printers.

As for crappy light sources, you just focus the light to a converging
beam onto a *small* pin-hole in shim metal, then re-converge the
diverging
beam from the other side. The pinhole cuts out rays that are not
following
the ideal lens 'ray-trace' path. By choosing suitable focal lengths, the
dot on the film will be smaller than the pin-hole size. Other tricks can
be done to make use of laser pointers too.

The mechanics are easy but fiddly. Mount a laser diode to a platform
that
moves along a finely threaded rod, driven with a stepper. An
anti-backlash
nut is made with two nuts with a spring in between. A printer mechanism
could be used.

http://pico-systems.com/photoplot.html

a tight cable and pulleys setup has worked for dot matrix printers for years for positioning back and forth. if you find the right old printer, that assembly can be removed and used, including the stepper.

for a tightly focused laser perhaps the laser assembly from a laser printer. it would work if you could mount it at the exact distance as it was in the original printer (it's focal point) from a new larger drum or platen(?i think that's the term).

of course, taking two printers apart to do the same thing a laser printer does anyway, may not be the most direct solution, but where's the fun in that?.

----- Original Message -----
From: Adam Seychell
To: Homebrew_PCBs@yahoogroups.com
Sent: Tuesday, April 09, 2002 10:03 PM
Subject: [Homebrew_PCBs] laser diode photoplotter


Hello group,
Has anyone here thought about building or even built a drum
photoplotter based on a red LED laser diode ? This would be used for
making printing masks, et. There has been much discussion among amateurs
on building a CNC mill/drill machines, however I am under the impression
that this is definitely NOT an task for the beginner, even if he/she
has access the right tools. A drum photoplotter appears simpler in
construction as there is only 1 axis required to position the light
head. Basically the drum plotter works by rotating a relatively large
drum with a film sensitive to red light (available from Kodak)
positioned around the outside of the drum. The drum spins at fairly high
speed (> 10 rev/sec) and the light source (red LED laser diode and
focusing lens) slowly and accurately moves along the length of the drum
in a straight line. The spinning drum sounds relatively simple to build.
The moving light source looks a lot more complicated / expensive. My
only thoughts how to go about this is to use a ball bearing screw and
linear bearing. I priced some ready to go ball screw guided assemblies
but the costs were prohibitive. Is there no other option ? I own a drill
press and a small lathe in my workshop. I am open to all comments.




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[Non-text portions of this message have been removed]

--- In Homebrew_PCBs@y..., Alexandre Guimarães <alexg@i...> wrote:

> Hi,
>
> > speed (> 10 rev/sec) and the light source (red LED laser diode and
>
>
> Usually cheap laser diodes are very bad source for points. The

light

> spreads unevenly and in a weird pattern. The optics to make it a

point

> source would probably end up being more expensive than using another

laser

> source.

Actually, this is not a big deal. A sphere lens collects the
light well, a piece of aluminum foil with a small hole masks
off the stray beams. A microfiche lens focuses a .001" spot
quite easily. The software is the killer! Also, the phase locked
loop to multiply a standard shaft encoder to a reasonable number
of pulses. I have made it work, though. See
http://pico-systems.com/photoplot.html for more details.