Dave N6NZ wrote:
On Jan 24, 2010, at 4:43 AM, Bob Paddock wrote:
CO2 laser is the wrong wavelength to cut metal. Only a couple percent of the
radiation is absorbed. Great for plastics, though, and many other materials. With
respect to >PCB etching, one thing I've thought about but haven't yet tried is
simply using paint. Apply a thin code of flat black paint as a resist (I'm guessing
enamel would work best) >and let the laser ablate the paint where you want to etch.
We already use commercial grade pre-photosensitized FR4 laminate, so
doing painting and such is not needed. My only concern was that there
might be issues of the wave-lengths between the LASER and the laminate
being miss-matched, but if the process is actually based on heat then
it is a non-issue.
Now that will depend on your photochemistry. CO2 laser is not in the visible
spectrum. You'd have to check the sensitivity of the photo emulsion w.r.t.
wavelength. Most litho films are not sensitive even to red, but do go up into
ultra-violet. I can't remember if CO2 is longer or shorter than visible light.
In any case, you'd get by with very low power.
So now for the wacky idea of the day... an interesting hack would be to make a
tool head for a RepRap or some other cheap X/Y bed that simply holds a green
laser pointer.
-dave
Dave,
I have been following the RepRap project with interest. A 3D printer
that anyone can make is a very cool scratch to itch. I am fascinated by
the artwork of the sculpter, Bathsheba Grossman. She really shows what
is possible with 3D printing. (http://www.bathsheba.com) Maybe the
RepRap will progress to this level of precision, eventually. I am very
impressed with the parts that people are currently making with it.
I like the idea of using a cnc mill to vector plot the pcb artwork onto
a photo-resist board with a laser. I do not think mounting a laser would
be very difficult. There must be a low intensity laser that is in the
correct frequency range to cure the resist. You could make different
apertures easily by creating transparent slides with a single white dot
against a black background.
As far as a cheap x/y bed, how about doing it with a cheap machine that
is massive and solid, like rock? I have been following the epoxy-granite
thread on cnczone.com for a long time:
http://www.cnczone.com/forums/showthread.php?t=30155 (It is a HUGE
thread with 3828 posts, currently.)
Epoxy-granite is basically moldable rock. It is made out of aggregates
of different sizes (mainly quartz), which are measured in certain
ratios, so that they pack together very tightly. The spaces between
where aggregates of one size touch are filled by smaller aggregates on
down through several orders of magnitude. The size of aggregates range
from 4mm in diameter down to a couple of microns. The epoxy (10-20% by
volume) is added to hold everything together.
Epoxy-granite is relatively cheap. It can approach the strength of
aluminum, but you can embed rebar in the casting to increase its tensile
strength. One of the nice properties of e/g is that it has 10 times the
damping properties of iron. That means better surface finish on the
machined parts, and longer tool life. Also, people should be able to
find most of the materials near local industrial centers. I have been
experimenting with e/g and I am currently building a benchtop cnc lathe.
I have a blog on it here:
http://www.cnczone.com/forums/showthread.php?t=42308
I am going to post many more pictures of my progress.
After, I finish the cnc lathe, I am on to a small epoxy-granite cnc
gantry mill. I think it will have a 13" x 13" table. My goal is a
massive, rigid, and accurate machine that can produce precision parts
and mill pcb's.
Thanks,
Dave
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