DIY

Crosscut Saw Sharpening

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The teeth of a crosscut saw might look something like this.
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Diagram shows the parts of a crosscut saw.
3 / 9
Diagram shows bevel and point of a typical cutter tooth.
4 / 9
Diagram shows method of positioning jointer to sharpen cutter teeth.
5 / 9
Diagram shows how to set up a jointer to file raker teeth.
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Gauging rakers with the pin gauge on the combination saw tool.
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Diagram show method of setting cutter teeth with a hammer and anvil.
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Diagram shows method of filing the outer edges of raker teeth, and the difference between swaged and straight raker teeth. 
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Diagram shows the spider tool.

Reprinted from Crosscut Saw Manual by Warren Miller
(available for $1.50 from the Superintendent of Documents,
U.S. Government Printing Office).


Opinions vary among saw filers as to the order of steps
followed in crosscut saw sharpening. Guidelines offered by saw
companies differ significantly. After examining the reasons
for the different orders, I’ve concluded the following
sequence is preferable.

Cleaning: removing rust or pitch.

Hammering: straightening a saw if it has bumps,
kinks, or twists in it.

Jointing: the means by which the tips or all the
cutter teeth are made to conform to the circle of the saw.

Raker fitting: includes shaping the raker gullet
and swaging and sharpening the raker.

Pointing up cutter teeth: filing the teeth sharp.

Setting: bending the tips of the cutter teeth away
from the plane of the saw, causing the kerf to be wider
than the blade.

These are the tools necessary for each operation.

Hammering: two steel straightedges about 10 to 14
inches long, a 3- to 4-pound cross-pein saw hammer (some
manufacturers call them cross-face hammers), a fairly flat
anvil.

Jointing: jointer (short or long), 7- or 8-inch special
crosscut file (mill bastard blunt file), saw vise.

Raker fitting: 7- or 8-inch slim taper
(triangular) file, pin gauge, raker gauge, hammer for swaging
(8- to 16-ounce tinner’s riveting hammer), 6-inch slim
taper file with “safe” corners (corners ground smooth),
6-inch mill bastard file, saw vise.

Pointing up cutter teeth: 7- or 8-inch special
crosscut file (mill bastard blunt file) for lance tooth
saws, 6- or 8-inch Great American crosscut file for
champion tooth saws, saw vise.

Setting: 8-ounce set hammer (or tinner’s riveting
hammer), setting stake or set tool or anvil, spider, saw
vise.

Saw Cleaning

Often a filer must clean a rusty or pitchy saw. One good
method is to lay the tool on a flat surface and clean with
an axe stone or a pumice grill stone. Liberally douse the
blade with kerosene or diesel oil to cut pitch and keep the
stone from plugging up with debris. Small kinks show up as
bright areas for high spots and dark places for
indentations. Use only enough pressure on the cutter teeth
to clean them… if metal is taken off the tips, both set
and tooth length will be affected.

Hammering or Straightening

Few saws are completely straight. Although slight kinks or
bumps won’t cause much trouble, a straight saw requires
minimum set and is less likely to buckle during the push
stroke when one person is sawing. And it will cut
straighter.

The saw to be straightened is hung vertically from one of
the handle holes.

Hold the straightedges lightly–one on each side of
the saw–so they are directly opposite each other. By
moving the devices back and forth as well as along the saw,
any kinks or bumps can be found. If you move the
straightedges with a slight twisting motion, quite small
kinks can be found by the difference in resistance. A
straightedge contacting the convex side of a kink will
twist easier than one on the concave surface.

When a kink is located, determine its shape and axis by
moving the straightedges over its surface. Mark its shape
with chalk or grease pencil (a wetted finger works well
too). Put the concave side down flat on the anvil,
and–with the appropriate face of your cross-pein
hammer–strike the saw several times over the kink.
(The appropriate face is the one that is fairly parallel to
the kink axis.) Check with straightedges and determine
further action. Take care to strike the saw with the face
of the hammer and not the edge. If done properly, the
hammer should leave no visible mark. A slightly
round-faced, 3-pound hammer can be used, but results aren’t
as good as with the cross-pein type.

If it should be impossible to acquire a straightedge
specifically for saw work, acceptable substitutes exist.
The characteristics of a desirable straightedge are that it
be light, stiff, and reasonably straight. A thickness from
0.050 to 0.100 inch is acceptable with the thinner
dimension being desirable. Possible substitutes might be
draftsman’s or machinist’s straightedges, or the rule from
a combination square.

Jointing the Saw

The number and variety of jointers are considerable, but
the principle is the same for all. They hold a file in such
a way that it can be run over the saw teeth to insure that
they all lie on the circle of the blade. There are short
and long jointers. The short jointer, generally part of a
combination saw tool, is by far the more common.

To use the short jointer, insert the file so it rests
flat on the supports (lugs) and adjust the screw
so the rasp bends to conform to the circle of the saw. Make
sure the surface of the file is square with the guide rails
on the body of the jointer … the tool may be warped or
improperly seated on the supports. Insert the file so it
runs in the normal filing direction (if used backwards, its
life will be severely shortened). Because a new rasp often
will cut faster than desired, a worn-out 7- or 8-inch
special crosscut file with the tang broken off works well.

Place the jointer on one end of the saw. Holding the tool
so the file rests on the cutter teeth, run the jointer the
length of the blade, using uniform downward pressure. This
is crucial if the circle of the saw is to be maintained. It
is also important to hold the guide rails on the body of
the jointer in contact with the side of the saw at all
times to assure that the file is square to the blade.

After the jointer has been run the length of the saw, look
at the teeth. If each tip has a shiny spot where the file
has just touched it, jointing is complete. If some teeth
are so short they weren’t touched, repeat the process until
all show the mark of the file. If a tooth has been chipped
or broken so it is much shorter than the rest, don’t worry
about it. No sense jointing the life out of a saw to make
it perfect.

Raker Fitting

For a saw to operate efficiently the raker teeth must
remove all the fiber severed by the cutter teeth, but no
more.

Because the cutting teeth exert pressure on the wood as
they cut, a certain thickness of wood is compressed and
springs back after the teeth pass over. As a result, fibers
are not severed quite as deeply as the teeth penetrate. Therefore the rakers following the cutters must be
shorter by the amount the wood springs back, so no
unsevered wood is removed.

Optimum depth is obtained by experiment, but figures vary
from 0.008 inch for hard or dry wood to 0.030 inch for
soft, springy wood; 0.012 inch is a good average figure
to begin with.

The depth of the rakers below the cutter teeth is
determined by using a tool called a raker gauge or raker
depth gauge–generally part of a combination saw filing
tool of which numerous varieties were manufactured. The
essential feature of all of them is a hardened steel filing
plate with a slot cut in it a little wider than the
thickness of a saw and a little longer than the distance
between the two tips on a raker. This is held on a frame in
such a way that when the gauge is placed over the raker, the
top of the filing plate is the same level as the desired
raker depth. The raker tips are cut to the level of the
plate with a file. The height of the filing plate is
adjustable.

One way of checking the setting of a raker gauge is to file
a raker using the tool. By placing a straightedge
between the two cutter teeth on each side of the filed
raker, you can measure the relative height with a feeler
gauge placed between the raker and straightedge.

There are two basic ways a raker can be shaped before it is
filed to its proper depth: straight or swaged. The straight
raker is by far the easier to file, but it results in a
relatively “slow” running saw. The swaged raker is
considerably more difficult to shape but results in a
superior tool. The reason for the difference is apparent
when one remembers that the raker acts like a chisel to
remove the shaving. Much less energy is required to remove
wood from a board if a chisel is held at a low angle to a
board than if it is held vertically. Swaging results in a
raker tip that is similar to a chisel held at a low angle
to the wood.

Fitting Straight Rakers

With a 7- or 8-inch slim taper file, dress (smooth) the
outside face of the rakers from the raker tip to the bottom
of the sawdust gullet. Make sure the file is held square
with the saw. This will provide clean, sound metal for the
cutting edge of the raker, cause less friction between the
outside face and the shaving, and aid shaving removal.

Next, file the raker to the proper depth. Place the
properly adjusted raker gauge on the saw so the raker fits
in the slot in the filing plate. Hold the gauge so it rests
firmly against the tops of the cutter teeth as well as the
side of the saw. Run a file across the raker tips until
they are even with the top of the filing plate. Once the
raker tip has been filed, the raker must be sharpened. With
a 7- or 8-inch slim taper file, shape the raker gullet into a “V” with slightly convex sides. Round the gullet out to the tip until the
flat spot on top almost disappears. If the tip is
overfiled, it changes the raker depth. If not filed enough,
the flat spot acts like a “sled runner” and does not permit
the edge to work properly.

Fitting Swaged Rakers

Swaging is forming the leading edge of the raker into a
curve so it more efficiently picks up the shaving. It is
done by striking a prepared raker tip on the inside face
with a hammer to bend the tip outward in a smooth curve. A
swaging hammer should have a face small enough to permit
you to strike the raker tip with the center of the face.
The best tool for swaging appears to be a tinner’s riveting
hammer.

To prepare the raker, file it approximately to a “V” using the slim taper file. The exact
shape depends on whether the raker is straight or has been
swaged before. The objective is to shape the tip so it can
be bent without breaking, but retain enough thickness to
prevent bending during use. For starters, the cutting angle
should be between 30 and 40 degrees.

The raker is now ready to be “swaged to the pin.” This
means bending the raker by striking the inside face of the
raker tip with a hammer until the tip just clears
a preset screw (called a pin) on a combination saw tool.

The pin is adjusted so the swaged raker is 0.002 to 0.003
inch higher than the finished raker depth. This is done by
first filing a raker to depth, using the raker gauge. Next,
place the pin gauge over the raker and adjust the pin
(screw) depth so a 0.002- or 0.003-inch feeler gauge will
just pass between the raker tip and the pin. Check
clearance again after tightening locknut.

To swage a raker, strike the raker tip a square blow, and
check the height with the pin gauge. If it is still too
high, continue alternately swaging and checking until the
raker tooth just clears the pin. Keep an eye on the shape
of the bend. The outside face of the raker should bend in
a smooth arc. A kinked raker tip will be difficult to swage
next time the saw is filed, and it will quite possibly
break. If the tip begins to kink, the hammer probably is
being used too high on the tip. If it won’t bend, the tip
may be too thick or the hammer is being used too low on the
tip. Often in the case of a new saw or a used saw with
straight rakers, it will be necessary to partially swage
the tip, then thin the tip some more with the file and
continue swaging.

There is no pat answer to the question: “At what angle is the raker struck?” This will vary with
the shape of the raker tip and must be learned from
experience. Keep an eye on the desired swage shape. Knowing where to strike the tip will come with experience.

Some saws are so hard and consequently brittle that there
is a possibility of breaking raker tips when swaging. If a
saw is so hard that a fairly new file keeps slipping while
the filer is shaping the raker gullets, or if a raker
actually breaks when being swaged, the rakers should be
tempered.

To temper the raker, polish one side of each raker until it
is shiny. Place the saw in a vise. Heat the top
three-fourths of the tooth uniformly, using a propane
torch. As it gets hotter, the color will go from light
straw, to brown, to deep purple, to dark blue, to light
blue, to a light yellow color. There are differing opinions
on how far to temper the rakers (what color to heat to). A
compromise seems to be between light blue and the second
yellow. A suggestion would be to first temper to light
blue, then–if trouble is still
experienced–temper again to the second light yellow.
Don’t heat into the body of the saw: It may cause the saw
to warp. Be very careful about playing the torch flame on
the raker tips. They heat very fast, making it extremely
easy to overheat them. This causes a soft raker that will
bend in hard wood and will not hold an edge.

Once the rakers are “swaged to the pin,” the tips are
dressed on the outside face. To dress the swaged tip a
6-inch slim taper file with “safe” corners is run lightly
across the under edge of the swage to square it up and
establish the rake angle. It is most important not to nick
the raker with the edge of a file. A nick can cause the tip
to break off during swaging or in use. This is the reason
for the ground “safe” corners on the dressing file. After
dressing the outside face and rake angle, joint exactly as
with the straightstyle raker. As with straight rakers, a
trial depth of 0.012 inch for average conditions is good.

The last step is to dress the sides of the rakers. The
swaging process often widens the raker at the tip. This can
be corrected by holding a 6-inch mill bastard file flat
against the raker and saw and making one or two light
vertical strokes.

Repairing Bent Rakers and Cutter Teeth

To check for bent rakers, make up a spider (set gauge) for
zero clearance on an unbent raker. A bent raker can easily
be found by using the spider in the same manner as for
checking a cutter tooth set.

To straighten a bent raker, the concave side of the raker
is placed on an anvil and hammered until tooth is straight.
Badly bent cutter teeth could be straightened the same way.

Broker Raker Tip

A broken raker tip allows the other tip on the raker to
bite too deeply on the cutting stroke, causing the saw to
catch just as it does with a long raker. File the unbroken
tip shorter, say 0.005 inch for starters. If it still
catches, file it even shorter.

Pointing Up Cutter Teeth

To point up the cutter teeth, tilt the vise away from you
at about a 45-degree angle. With the vise tilted, the flat
spot on each tooth caused by jointing should appear bright.
The main light source needs to be in front so you can see a
good reflection off the flat spot. A wide set of windows
(preferably facing north to avoid direct sunlight) works
well. If possible, avoid point sources of light such as
incandescent bulbs and direct sunlight.

For filing the teeth, a 7- or 8-inch special crosscut file
is used. The stroke should be more nearly up and down the
tooth than across. The main point to keep in mind when
filing a cutter tooth is to file just enough to
almost make the flat spot from the jointing
operation disappear. Overfiling upsets the relation between
the cutters and the rakers and also results in a weak
point. A slight rolling or rocking motion of the file
generates a slightly convex filed surface and results in a
more durable tooth. Because of the set, a tooth whose filed
surface is flat will develop a concave cutting edge and a
thin, weak point.

As the tooth is being filed, it is a good idea to
periodically remove the burr that forms on the back side
because it can obscure the true tooth shape. Remove the
burr with whetstone or a light stroke of the file
across the tooth back… just enough to remove the
burr
. The back side of the tooth must not be filed
because it may cause the saw to bind. The burr can also be
removed with a piece of hardwood.

After all the teeth are filed, run over them with a fine
stone held flat against the saw to remove any residual
burrs, especially at the tip of the tooth. A burr under the
spider would cause an error in the tooth set.

Setting Cutter Teeth

To set a saw is to bend the tip of each cutter tooth away
from the plane of the saw a slight amount. Just as
alternate teeth are sharpened opposite each other, they are
set opposite to each other. Setting helps prevent binding
by resulting in a kerf that is slightly wider than the saw.
The amount of set required depends on the type of saw used
and the type of wood being cut. A saw should be set only as
much as required to keep it from binding. More set than
necessary results in more work to make a wider kerf, and a
saw that flops … with the possibility of a curving cut.
The set required can vary from almost nothing for a
crescent-taper-ground saw in dry hardwood to 0.030 inch for
the same saw in soft, punky wood. A set of 0.010 inch is a
good figure to start with. Flat-ground saws require more
set.

There are several ways of hammer setting a saw, only one of
which is recommended because of its speed and accuracy. The
necessary tools are an 8-ounce set hammer, a set anvil, and
a spider (set gauge).

There doesn’t appear to be a current manufacturer for a
hammer specifically designed for setting. A setting hammer
should have a fairly small face. A large face such as most
ball-pein hammers have is difficult to use for setting
without hitting adjacent teeth. The best substitute for a
setting hammer appears to be a tinner’s riveting hammer
that weighs about 8 ounces.

There is no known current manufacturer for hand-held
anvils. Any piece of steel that can be held comfortably in
the hand and has a flat face and weighs about 2 pounds will
work. A piece of 1 1/2-inch-diameter shaft about 5 inches
long works admirably. It is not necessary to have a
bevel. Simply setting the tooth over the edge of the face
will work fine.

The spider (set gauge) is used to measure the tooth set. To
check the set for which the spider is adjusted, place it on
a flat surface so that the feet on the three short legs
contact the surface. With light pressure on the three short
legs, measure the clearance under the fourth foot (or
longer leg) with a feeler gauge. A piece of plate glass or a
mirror will work for the flat surface, though it is wise to
check the spider several places on the surface so errors
caused by irregularities can be averaged out.

As indicated earlier, a set of about 0.010 inch would
probably be satisfactory for average work for a felling
saw. More set is required for a heavy bucking saw, say
0.015 inch.

To adjust the spider for less set, place it on a flat
carborundum stone and, while putting pressure on the short
crosspiece, grind the feet down until it measures right.
For more set, shorten either end of the long crosspiece. It
is important that the foot at the end of the long leg is
flat and parallel to the plane defined by the other three
feet. This assures a constant reading no matter where the
tip of the cutter tooth contacts the foot. This can be
checked by lightly grinding that foot while the two feet on
the short crosspiece are in contact with the stone and
observing the resulting pattern on the foot.

To set the saw, place an anvil on the point side of the
tooth and strike the tooth on the beveled side with a set
hammer. The bevel on the anvil should be about 1/4 inch
below the tip of the tooth and the direction and placement
of the hammer blow such that the tip of the cutter tooth is
bent over the bevel. Be sure to strike the tooth squarely.
If it is struck a glancing blow with the edge of the hammer
face, the point of impact will be badly marred. This
sometimes work-hardens the metal enough that a file won’t
cut it. And it may make the tooth more susceptible to
breaking.

It is also important to keep the face of the anvil parallel
to the plane of the saw when setting. If it is held at an
angle, the tooth will be twisted when set. Check the set
with the spider. If the vertical legs rock, there is
insufficient set and the above procedure should be
repeated. If the horizontal legs rock, some of the set must
be taken out. This is done by moving the anvil nearly to
the top of the cutter tooth and striking a light blow.

Sometimes a tooth will have been bent from a point below
the filed part of the tooth. This can be determined by
checking with the spider up and down the tooth. If this is
the case, place the anvil on the tooth just below the bend
and straighten it by hammering the opposite side of the
tooth just above the anvil.