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David
E. Baker and Don Day
University of Missouri Extension
Table
1. Selecting a Chain Saw. |
Type
| Guide
bar length
| Use
|
Mini
or lightweight saws |
8
to 12 inches |
Light
and occasional use for limbing, cutting small logs and
felling very small trees. |
Midweight
saws |
14
to 20 inches |
Frequent
log cutting and felling of small trees. |
Heavyweight
saws |
Over
20 inches |
Professional
use, not generally recommended for consumers. |
Although
once used only by professional lumberjacks, chain saws are now
popular among many homeowners and farmers. Homeowners use them
to cut firewood and to do general tree trimming around their
homes. Farmers find them very useful for such jobs as clearing
land, trimming trees and cutting firewood.
However,
in the hands of a careless or inexperienced operator, chain
saws can be very hazardous. The U.S. Consumer Product Safety
Commission estimates that in 1979 approximately 50,000 people
required hospital treatment for injuries associated with chain
saws. Most accidents were caused by the operator coming into
contact with a moving chain saw blade. Injuries from a chain
saw are usually serious because they leave a jagged cut.
The
first step to safely operating a chain saw is selecting a saw
that fits your needs and is quiet, balanced and equipped with
safety features.
First,
you must decide whether a gasoline or electric chain saw is
best for you. Consider the following points when selecting
a saw.
Electric-powered
saws (Should be listed by the Underwriters' Laboratories (UL)):
- Require
a nearby, convenient source of electricity.
- Need
no fuel.
- Run
quietly.
- Start
easily and instantly.
- Are
limited in guide bar length (usually under 14 inches).
- Can
be used indoors.
- Have
potential for shock hazard.
- Usually
cost less.
- Vibrate
less.
- Have
no exhaust fumes.
Gasoline-powered
saws:
- Can
be used anywhere; not limited by electric cord.
- Use
gasoline-oil mixture as fuel.
- Are
relatively noisy and smokey.
- Require
some effort to start.
- Available
in many engine and guide-bar sizes.
- Intended
for outdoor use.
- Have
potential for fire or burn hazard.
Second,
consider the length of the guide bar. Match the bar size to
the type of job you expect to do most often.
Mini
or lightweight saws have 8- to 12-inch guide bars; they are
for light and occasional use for limbing, cutting small logs
and felling very small trees.
Midweight
saws have 14- to 20-inch guide bars; they can be used for
frequent log cutting and felling of small trees.
Heavyweight
saws have guide bars that are more than 20 inches long. These
saws are not generally recommended for non-professional saw
owners.
If the
guide bar is substantially longer than the thickness of the
wood to be cut, accidental contact between the guide bar tip
and a branch, the ground or other object could result in a
serious kickback injury.
If the
guide bar is too short, you will have to bury the tip of the
guide bar in the cut. Although most manufacturers indicate
that a saw can cut a log twice as thick as the guide bar,
burying the tip of the guide bar in the wood could also result
in a serious kickback injury.
First,
in preparing to operate the saw safely, read and study the operator's
manual. Even if you are an experienced operator, you should
periodically review safe operational procedures. If you buy
a used saw, ask the previous owner for the operator's manual
or write the saw manufacturer for a copy.
Before
you cut firewood or timber, outfit yourself with the proper
clothing and personal protective equipment that will help
reduce the possibility of a serious injury. Use the following
list as a guide.
- Clothing
should be well-fitted and free of dangling or ragged edges
that could become tangled in the saw. For additional protection,
use nylon mesh protective leg chaps and/or knee pads to
provide increased protection to your legs.
- A
hard hat protects your head from falling limbs or
branches. A properly fitted hat is cool, comfortable and
provides important protection from serious head injury.
- Safety
goggles or safety eye glasses with side shields prevent
injury from flying wood chips, twigs and sawdust.
- A
good pair of comfortable ear muffs or ear plugs protect
your ears from continual exposure to the 95 plus decibel
noise level from the saw.
- A
good pair of light-weight leather gloves protect
your hands from abrasions, splinters and cuts.
- A
pair of safety boots or shoes with high tops will
help protect your ankles in the event of accidental contact
with the moving saw blade. Steel toes will help protect
your feet from injury from falling limbs or logs.
A
saw in good condition is safer and easier to operate. Preventive
maintenance will allow you to cut more wood quickly and safely.
Maintenance includes sharp teeth, correct chain tension, proper
lubrication and a properly tuned engine. Check your operator's
manual for this maintenance information.
A
properly sharpened chain. If you notice that the chain
tends to walk sideways while cutting or the cut shows fine
powder instead of chips, or if you find yourself pressing
down hard to keep cutting or smell burnt wood, your saw needs
sharpening.
Follow
the instructions outlined in your owner's manual when sharpening
the chain. If you do your own sharpening, use the proper tools.
Wear gloves or use a rag over the chain to protect your hands
from the sharpened cutters.
Correct
chain tension. To assure good cutting action and a long
chain life, check chain tension. If too loose, a chain will
derail; if too tight, a chain will bind.
All
chains stretch with use. Most of the stretch occurs during
the first half hour of operation. Follow the manufacturer's
recommendation on chain tension. Most manufacturers recommend
that a cold chain be tightened to where the chain tie straps
hang away from the bar rail about 1/32 of an inch at the center
of the bar. A warm chain should be adjusted to a 1/8-inch
gap.
Proper
lubrication. Lubrication will prolong a chain's useful
life. On saws with automatic oilers, be sure the oiler is
properly adjusted so it doesn't over-oil and run dry during
operation. Remember that automatic oilers need an extra squirt
of oil occasionally.
Occasionally
the bar-oiling mechanism plugs up; serious damage to the saw
can result if this is not corrected. If the chain smokes while
operating, there is not enough lubrication. To check for bar
oiling, hold the saw tip above a light colored, dry surface
and accelerate the engine. Oil should spatter on the surface
if the oiler is operating properly. If not, remove the guide
bar and check the chain oil discharge slot.
Tool
kit. Every owner should have a good tool kit to help ensure
continued operation of the saw. The kit should contain the
following:
- A
few extra labeled cans or a plastic bottle (with attached
pouring nozzle) of chain oil.
- Wrenches
to fit all nuts and lugs on the saw.
- Screwdriver.
- Round
file and guide for touching up the chain.
- Flat
file and depth gauge to file the depth guides.
- Small
brush (1/2 inch) to clean away sawdust and wood chips from
around gas cap and cooling fins.
- Extra
spark plug.
- Owner's
manual (wrapped in a plastic bag).
- Cleaning
rags.
- Sharp
ax.
- Sledge
hammer and wedges.
- Multi-purpose
fire extinguisher.
- Shovel.
- Supply
of fuel in a UL-listed and/or FM-approved safety can.
- First
aid kit.
Refueling
and starting the engine. Since the chain saw engine is a
two-cycle engine, use the manufacturer's recommended fuel mixture.
When refueling the engine, use a funnel or flexible nozzle to
avoid spillage on the engine.
Only
refuel the engine when it is cool.
If fuel
is spilled, thoroughly clean the engine with the saw on the
ground and in an area cleared of combustible materials.
Do
not smoke during refueling.
Each
time you refuel, check the refill oiler, air filter, chain
tension and the tightness of all nuts, bolts and screws.
Starting
the engine. With one foot placed in the bracket to the
rear of the unit, start the saw engine on level ground. Set
the starting controls. Grip the top handle of the saw firmly
with one hand; use your other hand to pull the starting rope.
Smaller saws may not have a foot bracket, so make certain
the saw is held firmly on the ground. Never drop start the
saw.
Felling
procedures. Before you attempt to fell any tree, consider
its characteristics. One tree may lean, and another tree might
be unbalanced because of uneven top growth or breakage even
though the trunk doesn't lean. Large diameter branches are
also a good indicator of imbalance. Also consider wind conditions,
which can have a dramatic effect on the direction of fall.
Clear the ground. Before you start to cut, clear the
ground around the base of the tree of low or dead limbs, underbrush
and other obstructions. This precaution should provide clear
vision, unrestricted movement and an unhampered escape route
when the tree begins to fall (Figure 1).
A
felling and safety plan. In advance, plan your escape
route to either the rear or side, depending on the likely
direction of the fall. When the tree starts to go, shut the
saw off and drop it in a place that will allow an unhampered
escape.
When
you have determined a felling and safety plan, proceed as
follows:
- Hold
saw firmly with both hands.
- Make
a cut close to base of the tree but high enough to conveniently
avoid running saw into the ground.
- Cut
through trees up to 8 inches thick with one cut.
- On
larger trees, notch (undercut) at least one-third of trunk
diameter on fall side of trunk. Make lower cut of the 45-degree
notch first to prevent pinching or binding of the chain
by wedge.
- Make
felling or back cut on the opposite side of the trunk 2
inches above and parallel to the horizontal notch. Leave
wood fibers to act as a hinge to keep tree from twisting
and falling in the wrong direction or kicking back on the
stump. (See Figure 2).
- Keep
the guide bar in the middle of the cut (horizontal) so cutters
returning in the top groove do not re-cut. Guide saw into
tree. Do not force it. Rate of feed will depend on the size
and type of timber being cut.
- Remove
saw from cut and shut off before the tree falls.
- Cutting
completely through hinge fibers may allow tree to fall in
any direction, possibly on the retreating operator. Move
away from the tree at a 45-degree angle through the cleared
retreat lane.
Wedges.
A well-balanced tree may have to be wedged, pulled or pushed
to fall in a desired direction. Wedges are the most dependable
means of controlling the direction a tree will fall.
Use
two wedges rather than one to insure that the tree falls forward.
Use a sledge or mallet with a face at least 1/3 larger than
the breadth of the wedge. Strike squarely with firm, but not
excessive, blows. Careless blows may pop the wedge out, swinging
the tree backward. Using an ax head as a wedge or driver is
dangerous. The steel is likely to splinter, and flying particles
might strike the user.
After
the tree is on the ground, take a look at each limb before
making the cut to be sure that cutting the limb off will not
bind the guide bar or cause the trunk to roll toward the operator.
Do not
face the limb squarely. Stand at a 45-degree angle so that
if the saw slips or completes the cut sooner than expected,
the chain will not strike your leg.
Sawing
with the point of the guide bar (nose sawing) greatly increases
the chances of chain saw kickback (Figure 3). If the chain
suddenly hits a solid object or takes too large of a cut,
then the saw may be forced backward. This could result in
a serious accident.
Preventing
kickback. Follow these steps to prevent kickback:
- Hold
the saw firmly with both hands.
- Grip
the top handle by putting your thumb around it.
- Use
a saw equipped with a chain-brake or kickback guard.
- Watch
for twigs that can snag the chain.
- Don't
pinch the bar while cutting the log.
- Saw
with the lower part of the bar close to the bumper, not
on the top near the nose.
- Maintain
high saw speed when entering or leaving a cut in the wood.
- Keep
the chain sharp.
- Don't
reach above shoulder height to cut. The chain is too close
to your face in this position.
Never make
cuts with the saw between your legs. Never straddle the limb
you are cutting. Always be aware of the direction the chain
will go if it breaks, and keep people clear of this area. Stand
on the side of the trunk opposite the limb you are cutting.
While
limbing or cutting the trunk (bucking), make sure the chain
does not hit the ground. An operator can cut 40 trees and
not damage the chain the way striking the ground one time
can.
If
the trunk is supported along its entire length, overbuck. To
overbuck, make cuts into 1/3 of the diameter of the log from
the top down the length of the trunk. Then roll the log over
and make the final cuts. This procedure prevents pinching the
guide bar and chain (Figure 4).
If the
log is supported on one end, make the first cut from the underside
1/3 the diameter of the log (underbuck). Then complete the
cut from the topside (overbuck) (Figure 5).
When
the log is supported from both ends, cut 1/3 the diameter
from the top (overbuck) then complete the cut by cutting upward
from the underside (underbuck) to meet the first cut (Figure
6).
Whenever
the saw is being operated, keep people well out of the cutting
area. If a person is assisting by removing limbs, be aware
of your assistant's position and activity at all times.
When
cutting logs with a large diameter, operate the saw with the
throttle about three-quarters open. Overpowering the saw will
waste fuel and create unnecessary wear. Under-powering will
not push enough air through the cooling fins and may cause
engine overheating. A saw buck is a handy device for safely
cutting wood to the proper length. You can find plans in your
owner's manual or at your local library.
Electrically
powered chain saws require some special safety precautions.
Use only a three-wire cord of the proper size with three-pronged
plugs and a grounded three-wire outlet. A ground fault interrupter
in the power supply line will help prevent fatal shocks.
The
soil in the work area should be relatively dry. Avoid working
in areas where foliage or the ground is wet.
Lay
out the cord so it will not interfere with your work. Take
care to place it so that you don't inadvertently cut it with
the saw or trip on it.
Make
sure the saw switch is in the "off" position before completing
the electrical connection. Always unplug the power before
making adjustments and when the saw is not in use.
For
transport, set the saw level with the gas cap up. Be sure the
saw cannot tip over and spill gasoline. Avoid carrying the saw
in the passenger area of a vehicle. Protect yourself and the
chain. Use a chain guard or a carrying case to protect yourself
as well as the chain.
For
storage, drain the fuel tank in a safe area. Run the engine
at idle until it stops to remove the remaining gas from the
engine. Remove the chain and store it in a container of oil.
Disconnect the spark plug wire to reduce the possibility of
accidental starting. Store the saw out of reach of children.
Balance.
Saws should not tip to either side or rock back with the guide
bar tilting toward the operator. The saw should feel balanced
and comfortable.
Hand
guard. This is a bar in front of the forward handle that
keeps the left hand from slipping onto the chain.
Chain
brake (Gasoline only). This feature is designed to stop
the chain in a fraction of a second if a kickback occurs,
thus reducing the chances of serious injury. A chain brake
can also serve as hand guard.
Spark
arrester (Gasoline only). A spark arrester keeps sparks
from being ejected by the exhaust. It is required in some
areas of the country.
Safety
tip. A safety tip covers the chain as it passes around
the nose of the guide bar. It reduces the chance of kickback
by keeping the chain from contacting anything at the guide
bar tip.
Trigger
or throttle lockout. This feature guards against inadvertent
saw chain motion.
Chain
catcher. A chain catcher helps with electrical safety.
If you choose an electric chain saw, select one that has been
UL listed.
Vibration
reduction system. Rubber bushings between the handle and
saw body or on the engine mountings help reduce the vibration
you feel when sawing. This reduces fatigue.
Bumper
spikes. Most saws have large spikes on the front of the
engine or motor housing that grip the wood and help hold the
saw in place during cutting.
Automatic
chain oiling. This feature automatically oils the chain.
Automatic
chain sharpening. This helps keep the chain sharp while
on the job. Manual sharpening should still be performed every
three to four hours of use. Excessive use causes chain wear.
Compression
release (Gasoline only). This makes starting large engines
much easier.
Case
and/or chain sheath. This protects the saw from dirt during
storage and transfer.
Adjustment
tool. This is a tool with the proper wrench sizes for
adjusting the chain and removing spark plugs.
Table
2. Chain saw troubleshooting guide. |
Symptom
| Problem
| Correction
|
Difficult
or poor cutting |
Chain
dull |
Sharpen
chain |
|
Improperly
sharpened chain |
Check
chain |
|
Chain
installed backward |
Turn
chain around |
|
Improper
chain tension |
Correct
chain tension |
|
Bar
and chain aren't being lubed |
Fill
oil tank, adjust oiler |
|
Damaged
guide bar |
Inspect
guide bar |
|
Exhaust
ports dirty |
Clean
muffler and exhaust ports |
|
Fuel
filter dirty |
Clean
fuel filter |
|
Improperly
adjusted carburetor |
Adjust
carburetor |
Oiler
not working |
Out
of oil |
Fill
oil tank |
|
Oil
hole plugged |
Clean
oil supply hole |
|
Oil
strainer dirty |
Clean
oil strainer |
|
Oiler
adjusted incorrectly |
Adjust
oiler |
|
Plugged
vent on oil tank cap |
Clean
vent on oil tank cap |
Engine
won't start |
Improper
starting procedure |
Follow
correct procedure |
|
Fuel
tank empty |
Fill
fuel tank |
|
Engine
flooded |
Clean
spark plug |
|
Carburetor
adjustment incorrect |
Adjust
carburetor |
|
Spark
plug fouled |
Clean
or replace plug |
Engine
dies or accelerates poorly |
Fuel
tank empty |
Fill
fuel tank |
|
Air
cleaner dirty |
Clean
air cleaner |
|
Spark
plug fouled |
Clean
or replace plug |
|
Carburetor
adjustment incorrect |
Adjust
carburetor |
|
Plugged
vent on fuel tank cap |
Clean
vent on fuel tank cap |
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Disclaimer
and Reproduction Information: Information in NASD does not represent
NIOSH policy. Information included in NASD appears by permission
of the author and/or copyright holder. More
NASD Review: 04/2002
This
document is
GO1959
,
a series of the University Extension, the University of Missouri-Columbia,
Columbia, MO 65211. Publication date: October 1993.
David
E. Baker, Department of Agricultural Engineering, and Don
Day, Area Agricultural Engineering Specialist, University
of Missouri-Columbia, Columbia, MO 65211.
|