Trx250r180
Saw polisher
Iron, I am the amateur here at this, but perhaps that means I can help (just learned it recently myself).
Most all the files used for square file are 6 sided (except the goofy). I'm using the PFERD Chislel Bit Three Square (Looks like a triangle file with flat corners). Perhaps I'll graduate to the Chisel Bit Flat like Brian, but not yet, my files resembles a round fie.
Study the sharpening angles in the Madsen's website. (I'm using Stihl RSL or RSLK I think they are the same).
As Brian & mdavlee stated, you file from the outside in, instead of the inside out. I try to picture both the top plate angle and side plate angle as being 45 degrees. (which will result in an outside top plate angle of about 20 degrees).
Holding the file at about 45 degrees for both cutters, make sure the corner of the file stays in the corner of the tooth and that the wider side of the file is flush with the top plate (no gap). As you stroke, in addition to going straight, put slight pressure toward the corner. Following the original angles is the best way to learn.
I hope this helps, and if any of you guys with more experience have any additions or corrections to what I have stated, please post them. I think I'm doing it right, but I'm just learning.
the original angles are not too good in my opinion ,just a compromise for longer service life ,but not sharp