Yeah, 12 points and above... you either must have ‘young eyes’, or good
magnification. Maybe both. And bright raking light.
On a 16 pt saw, a single erroneous stroke can ‘disappear’ a whole tooth,
especially if you are using a ‘too-big’ file. Yeah, I’ve done it. But, if
you know how to sharpen a 7 point, you can certainly do a 12 point. It
ain’t rocket surgery, and the only way we get better at anything is by
practice. Make mistakes and learn from them. So start with a junker, and
I’ve even totally removed all the ugly teeth (all “sergeants and
sappers”) on a junk $1 saw and cut in new teeth, using a home made
template to cut in new gullets with a (gulp) mini-hacksaw (Paul Sellers has
a free video on how to do it that is worth watching ...and trying). This
saves your file- the corner of the saw file is the part that breaks down
first, especially on old saws with irregular tempering. When you look at
used saw files under magnification, you’ll see that the file teeth are
broken off only along the very corner, and no where else. There’s actually
a tiny flat along the corner of the file, otherwise you couldn’t sink the
corner of the file into the saw plate. The smaller the saw file, the
narrower the flat. Maybe we shouldn’t call them 3 sided files (since there
are six sides if we include these tiny flats)?
Once you have the depth of the gullet cut, shaping the tooth is easy.
All galoots have junk saws lying around, right? Just start doing it, you
can always bury your mistakes. No one has to know.
But I’ll bet after a couple of hours you’ll be passable, and after a couple
dozen hours you’ll be pretty good at it.