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A guideto
chain saw
chain sharpening
The chain saw is one of an arborist’s most important tools. A well-maintained saw with a sharp
chain will help make the job run smoothly and profitably. A dull chain causes both the saw and the
saw user to work harder and actually makes the chain saw more dangerous and prone to kickback.
Proper chain sharpening has become something of a lost art, as many users actually waste a lot of
chain and cause the saw to cut poorly because of improper sharpening.
Prior to talking about sharpening, it is important that we
understand the different parts of the cutter tooth and
how the chain is designed to cut. There are five parts of
the cutter tooth that work together to make the chain cut
properly.
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First is the depth gauge. Often called a raker, guide or
drag, the depth gauge sits in front of
the cutter tooth. The clearance from
the top of the depth gauge to the
cutter tooth sets up the thickness of
the chip. Generally this is designed
to be between 25 and 30 one-thousandths of an inch.
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2
Second is the working corner,
which is rounded on a semi-chisel chain
and pointed (hence called the point) on
a full-chisel chain. This working corner
starts the cut; if it has been damaged,
the chain won’t cut properly.
Third is the top of the tooth or the top plate. The
top plate angle is the angle at which
the chain is sharpened, usually 25 or
30 degrees. On many chains there is
a line on the rear of the top plate. This
is the witness mark, showing that the
chain can be sharpened back to that
line and still cut effectively. It is also
parallel to the top plate angle and may
be used as a filing guide.
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4
Fourth is the bottom of the
top plate, also known as
the chisel. The chain cuts by
chiseling off a chip of wood. The
chisel angle is normally between 45
and 60 degrees.
Fifth is the side plate, this severs the chip. The
side plate angle is often the same
as the chisel angle depending on
the type of chain and the filing
technique. It is important to have a
razor edge on both the side and top
plates, with no nicks or shiny spots.
There are numerous ways to sharpen chain: bench grinding,
using dremel tools, round filing and square bit filing. We will
focus here on round filing, but it is important with any sharpening technique that the user gets proper training with those
specific tools in order to use them effectively.
While it is important to have a sharply defined point and
sharp top and side plates, it is also important to try and
maintain the same working angles on the various parts of
the cutting tooth as when it was new. Some people suggest
its better to increase the top plate angle, to between 35 and
45 degrees; the chain will cut faster because there was less
chain traveling through the wood. Experience has shown
that this may help somewhat in soft wood but definitely not
in hard wood. In addition, this technique exposes more of
the point and thins out the side plate, making it much easier
to dull the chain.
One of the hardest things when round
filing by hand is to hold the file in the
in the proper position with 20 percent
of the file visible above the tooth, so
that the chain is sharpened and the
tooth angles are maintained. A
common mistake is to put too much
down pressure on the file,
eventually putting the file under
the tooth, creating a hooked
tooth and changing the side
plate and chisel angles.
The chain will cut rough and hardly ever cut straight. The
opposite to this is pulling up and into the tooth with the
file too much as you sharpen. This can
flatten out the chisel angle and side plate
angle leading to the chain not feeding into
the wood and not cutting well. Learning
to place the file on the tooth in the correct
position during sharpening is very
challenging
physically and
mentally. Therefore I have found that
there are a few different filing guides
that can make the job much easier.
Before looking at these filing guides,
let’s make sure we have the right tools. A vise is a nice way
to immobilize your chain saw and allows you to sharpen with
both hands on the file. A stump vise will allow you to easily
file out on the jobsite. Make sure you know what size chain
you have on your saw so you know what size file and filing
guide(s) to use.
Filing from the outside will chip the chrome on the side
plate. File the tooth back until you get a nicely defined point
and a razor-sharp top plate edge. If the leading edge is shiny,
the chrome plating has been chipped off. It is important to
bring the edge back until you get the dull chrome-plated
finish along the edge. Generally, try to keep the file level
when sharpening, as there is already an 8 degree angle on
the tooth.
Oregon makes a chain-filing plate for the file to sit in (refer
to the video). Simply lay the file plate on top of the tooth you
are sharpening, and it sets the file on the tooth in the correct
position. Line angles on the top of the plate help you set up
the proper filing angle. Another handy tool is the roller-guide.
This sits on top of the bar/chain tooth. Push the file along
the tooth with gentle strokes so that both rollers
move. Once again this puts the file on the tooth
in the correct position. I usually use the witness
mark on the tooth to line up my filing angle. After
filing all the teeth, it is important to set the depth
gauges. There a number of different types of
depth gauge plates; probably the easiest comes
with the roller guide combo. Lay the plate on top
of the filed tooth with the depth gauge protruding up through
the hole in the plate. Take a flat file and file the depth gauge
down to the plate. Now you have set the depth gauge to that
tooth. While the best cutting occurs when all the teeth are
the same size, because the chain is well balanced, the most
important thing is to have each tooth sharp and have each
depth gauge set to that tooth so all the teeth are taking the
same amount of bite when cutting.
A very handy two-in-one filing guide is the Husqvarna Sharp
Force guide. This unit uses both a round file and flat file
and takes down the depth gauges at the same time you
are sharpening the tooth. This is very useful for touch-ups
out in the field. The Sharp Force tool must be used on a full
complement chain, as the file guide rides on top of the tooth
you are sharpening and the tooth in front of it.
Just when you thought it couldn’t get any easier, along
comes the new Power Sharp precision saw chain sharpening
system from Oregon. This system will allow you to sharpen
your chain in as little as three to five seconds. For a closer
look visit http://www.powersharp.com/powersharp_video.asp
Most cutting in the tree-care industry is done with three
different sizes of chain pitch. The pitch of the chain is the
distance between any three consecutive rivets, divided
by two. A three-eighth-inch pitch chain generally uses a
7/32-inch file, a .325-inch pitch chain uses a 3/16-inch file
and a 3/8-inch low-profile chain uses a 5/32-inch file.
If you are using a file guide, make sure it is for the correct
size chain. When filing, the file cuts on the push motion, not
the pull. Dragging the file back and forth will only dull the file.
It is also important to file from the inside of the tooth out.
Any of these handy filing guides can help make sharpening a
little less burdensome. Of course, a good sawyer who keeps
the bar/chain out of the dirt will need to spend a lot less
time sharpening their chain. A sharp chain will make the job
easier and safer — and allow the saw to do the work. A dull
chain requires the operator to push harder on the saw, which
leads to more wear of the bar and sprocket.
So, when using a chain saw, please remember to work
safely, wear the proper personal protective equipment and
keep both hands on the saw — an make sure the chain is
properly sharpened.
By Rip Tompkins, ArborMaster, Inc