Good advise zootfoot - I'd add late at night when tired to that as well.
If using power tools remember to clamp the panel down well.
The non-reinforced cutting disks don't last long on steel or thick aluminum.
Only done one myself - and made a pig's ear of the cutting (dremal disks on full size drill
![Frown :( :(](/styles/default/xenforo/vbSmilies/Normal/frown.gif)
)
Re-marked out the window 2mm larger and used a grinding stone bit to 'sand' the metal to the right shape. Finished with a file.
Couldn't find a hacksaw that would work for a window (space between blade and frame was to small)
For the £10-15, a metal work shop will charge you - it's not worth buying the tools.
Killing a £200 Silverstone or Lian Li on your first 'cutting' mod is not worth the 'I did it all myself' brownie points.
In your case a 300 is a good case to learn as it's relatively easy to get replacement panels if it does all go pear shaped.
If your
not going to respray/powercoat the case then protect the paint work.
Masking tape and some care go a long way to make the overall process as painless as possable