yes, that was with a grinder. 50 degrees with a file as the hollow grind will weaken it. So he says. He first dresses the wheel to have a flat side on the bottom of the cut so as not to hit the links, then rounds the left side of the wheel.
HERE IT IS
Chain Modification
Regular chain, beveled across the fronts of
the cutters a t 30°, enters the kerf at an angle,
whic h can cause excessive side pressure o n
cutters and drive links. When chain is gro und
this way, the corner of each cutter becomes
the prime cutting a rea; once th at a rea dulls,
cu tt ing ab il ity is greatly reduced. To solve
thi s problem, I grind my ripping chain cu tte rs
straight across the front s with th e shape d
grinding stone adjusted 50° from vertical (40°
from horizontal ). This is the way commercia l
sawmills grind their blades for circular saws,
gangsaws and bandsaws.
Hand-Filing
Chain modification with a file guide and
round file is essentially the same as with a
grinder, but when modifying by hand, I file a
45° hook on each cutter instead of a 50° hook.
This is because the round file leaves an edge
that is hollow-ground; if the hook were filed
to 50°, the cutting edge would be weakened.
To modify my .404-pi tch, .063-gauge 52L Oregon
chain, I use the Oregon model #25892 file
guide and a ~ z- i n . round file. Start off with the
file diameter recommended for your chain,
but switch to the next smallest size (Y32 in. less)
when the cutters of the chain are about halfworn.
Don't assume the file guide will be
straight when you take it out of the package check
yours and straighten it out if necessary.
The file guide, as it comes from the manufacturer,
is set to file a hook angle of approximately
50-to increase the angle, it is necessary
to shim the file in the guide at both ends,
directly under both clamps (1). I usually use
two or three strips of a matchbook cover to
start, adding strips until the file cuts a 45°
hook. It's a good idea to start with a conservative
number of strips, to avoid removing too
much metal. For an example of shim thickne
ss, with the 7hz-in. file and guide I'm using
here, the shim measures .060 in.
When hand-filing inthe shop (and especially
for initial chain modification), I prefer to hold
the chain in a small machinist's vise, rather
than to file while the chain is on the bar. (When
sharpening in the field, when the chain is on
the bar, I mount the bar in a holder made especially
for field work.) With a square, draw a '
line 90° across the jaws of the vise, then mount
you r chain. Position the file guide flat on top
of the first cutter, touching the depth gauge,
and keep the guide parallel to the line (2).
CHAPTER 3 The Chain
With both hands, fil e in long, controlled
strokes, using the full length of th e fil e. Don't
drag the file on the back s t roke, as thi s will
wear it out. Remember to keep th e guide flat
on top of the cutter. Keep filing until the hook
angle on the side of the cutter is 45° and the top
plate is 90° across (3). The bottom of the cutter
gullet should be just above the tops of the drive
links. To speed things up, I sometimes file the
cutter back freehand, then u se th e guide to
complete the modification accuratel y.
As you modify yo u r chain, measure th e length
of the top plate of th e cutters to make sure
that they are all exactly th e same. You can use
a crescent wrench or calipe r for a gauge.
It's a good idea to rotate th e fil e in th e guide
slightly as you feel it s ta r t to dull. At least two
files will usually be necessary to modify one
chain. Never use a dull file to modify or
sharpen chain-it's a waste of time.
