I found out today that the Linux printing software (Gutenprint) now
supports my R280 printer (the R280 came with a camera, I've mentioned
this before). So now I can control the dots more accurately.
However, it seems that the printer just can't position a dot with,
say, 1 mil of accuracy. I haven't done much experimenting with the
driver to try to reduce the variables that are causing this variation
(like weaving method). Note that this is with unidirectional
printing; bidirectional makes it much worse. The printer is 5760 x
2880 DPI, I've been using 2880x2880 for my tests.
Even so, if I can solve the bleeding problem (see below), it looks
like 4 mil can be done, maybe 5-6 mil reliably. Assuming the
photoresist doesn't make things worse. I haven't tried doing anything
with these plots other than plotting them and looking at them under a
microscope.
Fortunately, Gutenprint allows you to adjust the ink density.
I've experimented with values from 0.8 (the default) up to 2.0. I've
found that 2.0 gives a really dark print - pretty much solid - but the
ink quickly bleeds on my vellum, corrupting the print. Any tips on
that? Heat gun? (tried - it takes long enough to print that the
bleeding happens before I can get the page out) Less ink leaves spotty
results, so for this to work with these inks, I'd need to be able to
print at 2.0 without ink bleeding.
Also - I've figure out my Vellum problem (paper "jam"). Putting a
small piece of masking tape in the upper right corner of the vellum
lets the printer see the leading edge, so it won't reject the paper.
The tape can go on the front or back of the vellum.
The R280 has a cd-rom tray, but I haven't tried printing directly to
copper yet (resist) or to copper with photofilm on it. I suspect the
results will be no better than on the vellum.
http://www.delorie.com/pcb/r280/DJ