Being plagued by the lack of local timing belt
suppliers able to provide 5mm belts, and having
bought 2 meters of 10.3 wide T2.5 belts, I had to
cut 'em to 5mm.

After reading this:

blog.reprap.org/2009_08_01_archive.html

and having no way to print the jig until my printer was finished,
I designed the cnc-able version of this.

This iteration has a larger 3mm wide slot for the blade, this way you can use
whatever washers you have available to adjust the blade position
in order to avoid the lengthwise metal strands inside the timing belt.

Do a test cut by assembling the jig and feeding a few mm of timing belt until it hits the blade.
It might take a bit of force.

Remove it and check / measure if the cut is as wide as you want, and if it doesn't hit the metal strands.
Adjust as needed by adding, removing and changing the order of the stack of washers, until your cut works.
see pictures.

ATTENTION - this was designed for 10.3mm wide belts, you can edit the vector file by changing the belt slot width
( the central vertical thin rectangle), and using your own software tools to regenerate the gcode toolpaths.

BE CAREFUL when using it, as you'll have a blade sticking out of the jig. Securely clamp it to a stable working bench/table (see pics),
work slowly until you're done, and disassemble/remove the blade as soon as you're done. This is dangerous for children/pets/you. Be prudent.

Assembly: use 4x m3x22mm bolts, nuts and washers, 10mm standoffs, and a c-clamp or vise . see pictures.

You can find the gcode (emc2 mm arcs .gnc) for 9.4mm MDF, 3mm end-mills and
very slow speeds to accommodate small desktop cncs here. It takes forever to mill because I added ramping motion to the file to remedy dull endmills. Edit it to fix that.
This is tested and working fine.