I'm using the slot cutter again cutting a couple of mm in from
the line. It would probably be better to use a jigsaw to be honest but it's at home
and I've been waiting for this cut.
The first cut is pretty rough, then I use a
grinding wheel to take it a bit closer to the line, then use a file to clean off the
chunks of melted plastic, then stick with the file for the last 1mm.
Obviously this takes quite a long time, with lots of checking against the screen, and
using a magazine as a sharp right angle to check for straightness. After an hour
of grinding, cutting and filing I've got a neat straight edged hole.