It's not difficult.
All you need is a SG$7 carbite cutter available from any DIY shop, a steel rule, a small bottle of machine oil (the type for your grandma's sewing machine), some thin paper to place between the filter and ruler, some common silicon carbite sandpaper in fine and course grades (also available from all DIY shops) and a few sheets of waste glass for practice.
Steps:1. Draw an outline of the IRC/AA filter you're gonna replace on the IR filter of your choice, use a very fine, waterbased CD/DVD marker. The measurements can be found here:
http://www.irphotography.org/index.ir?showtopic=2482. Place a piece of paper between your ruler and filter, oil the line to be cut
WITH A GENEROUS AMOUNT OF OIL and cut the filter using firm and consistant preasure. You don't need a lot of strength. You should hear a sound like the ripping of cloth. Start and stop about 2-3mm from each edge.
3. Holding the filter in your hands with the cut line in between both hands, gently "snap" the filter back. It will break cleanly along the line.
4.
DO NOT WIPE THE FILTER AFTER EACH CUT, INSTEAD, RINSE IT GENTLY WITH SOAP AND WATER. THIS PREVENTS THE TINY GLASS FRAGMENTS FROM SCRATCHING THE FILTER.5. Repeat steps 2 to 4 for each edge.
6. When done, you'll find that the filter will be a little longer and wider than necessary. Just grind it down, first with the course sandpaper than with the fine. Be sure to put lots of water on the sandpaper.
That's it.
Tipsa. Practice, practice, practice...look around for waste glass to practice cutting on, make sure it's not tampered glass
b. When cutting, be sure to apply a firm, even preasure. When done correctly, you WILL hear a sound like cloth ripping.
c. Always use lots of oil and always clean up after each cut. This will help you avoid unwanted scratches.
d. When snapping the filter at the cut point, use your hands or a pair of padded pliers. NEVER use the notches on the cutter itself.
Cheers,
Matt