only filter needles have filters... not all needles...
no offense, but your way sounds retarded.
one reason i love turkish primos... just look at the amp, aim the blue dot towards you, and snap away from you. no tools, no mess, no bullshit, the amps come prescored on one side.
otherwise i use a serrated kitchen knife to score the amp, not hard, not even enough to make a noticeable line, just spin the amp in the serrated edge a couple of times and snap away. i draw w/an 18 when using amps