[MrForbes]

I used a hammer and cold chisel, split the gear in half lengthwise, very quick and easy. Support the gear on a big chunk of solid metal like the anvil part of a bench vice or a heavy welding table, put the chisel in the space between the two topmost teeth, and give it a good whack with a big hammer.

Needless to say the gear will not be useable after this operation.