Karl Townsend wrote:
The roadside signs announcing my business need replacing...

With a huge laborious effort, I now have the sign as an AutoCAD file. My
next step is to have the lines burned/cut into a material so I can make a
stencil. There are a few sections in the sign where the stencil will be only
1/2" wide and a lot where the stencil will be 1" wide. The sign measures 48"
by 96" (4'x8').

So, what would be the best material to use? I can reinforce the very thin
sections mentioned above but not all the 1" wide sections. If I go with
plasma cut steel, I'm guessing I need to go all the way up to 1/8" thick
making the stencil weight a ton. I'm afraid thinner sections will warp and
make painting no fun at all.

I did a 4' x 8' sign for a friends business a few years ago by plotting
the sign on ordinary plotter paper and then cut it out with an Exacto
knife. I painted the plywood the base color with exterior enamel and a
roller. Once it was well sealed for weather, I put the stencil on the
board and spray painted the signage with a rattle can. It took a few
coats with the rattle can. When it was done, it looked great from 10'
and held up for 5+ years in the New Mexico sun and mild winters.

The stencil only survived the one use, but would have been simple to
reproduce.

One of the things I did that helped was to spray the back side of the
stencil around the characters with artists mounting adhesive. It helped
the stencil stay tight on the board until it was completely done, but
came up cleanly with careful pulling.

Good Luck,
Bob