All this plastic cutting discussion takes me back to the signcrafting days. Where be me old sword stripers...
The abrasive flex blade, "abafile" or other trade names, is an excellent idea; particularly useful for curved cuts.
With whatever
combination of cutting tools you use, be sure to adequately secure the plastic substrate as close to the cut line as possible. Try to prevent the plastic from flexing, thus avoiding potential cracking.
Also, use some low-tack tape to cover the plastic and protect it from scratches caused by clamping, sawing, or even just handling the screen.
I found that a flat Vixen file will quickly dress the edges to the final trim line.
http://www.simonds.cc/files/vix-flatwithtang.php?menu=mnuPFiles Use the same precautions utilized during the initial cutting evolution.
A small, medium-hard sanding block (available at auto body supply stores, as is the Vixen file) and progressively finer wet/dry papers -used wet- will polish the edge to a pleasing finish. You can go as far as you have the patience with wet sanding to achieve a smooth matte or high gloss edge. Rinse frequently but avoid scratches by not rag wiping.
Working the plastic is fairly simple. The key is protecting the material during the shaping.
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