Homebrew PCBs

I've gotten down to 8.33 mil with TT with a fair degree of
reliability.  6.66 I can do if I'm careful and put extra copies of the
board on the print - there's usually one short or open somewhere,
often I can fix it with a knife or solder.  Note the off-mil sizes; my
laser printer is 600dpi or 1.33 mil per pixel, so I use multiples of
that to get consistent results.  The limitation with my printer is its
ability to place the toner particles precisely.

With photomask I've been able to do 6 mil with high reliability, and 5
if I'm careful.  In theory I can do 4, but I haven't needed to try to
get that to work since I don't use parts that small.  The limitation
here, with my printer, seems to be its ability to feed the paper
accurately.  Quarter sheets are too small for a good grip, half sheets
work much better.