A few things help me get better results, mainly by making it easier visually:
- A light source shining from behind the teeth. Position this light so the flat tops light up by the reflection. This makes a big difference after jointing the teeth, seeing the flat tops disappearing by filing. note: A wide light source like a row of leds lights up more teeth at once. A light bulb or spot needs to be moved along the saw to keep seeing the reflections as you go along the saw.
- A saw vise that can raise the teeth closer to your eyes when making the last passes with the file. Especially with small teeth this makes a big difference. (You could also sit down at the bench vise.) With very small teeth a pair of magnifying glasses also helps a lot.
- A filing guide that magnifies the angles of the file. Like winding sticks magnify the twist in a board, a filing guide can make it a lot easier to present the file consistently to each tooth.
- A file holder for jointing the teeth makes it easier to keep the file exactly 90 degrees to the saw plate.
There are a few filing guides available on the market, like the Veritas for instance. The Veritas clamps to the tip of the file. It’s also easy to make one from a block of wood.
After seeing Gerd Fritsche’s version I tried the guide at the handle side and made the above version. The advantage is that the tapered tip of the file can be fully used at the beginning of the stroke.