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Teacher
Edition Contents
Skill,
Tools, & Craftsmanship
Cutting
& Drying Fish
Sharpening
Nails,
Pegs, & Lashings
Falling
Trees &
Small-Scale
Logging
Guns
Chainsaw
Clutch & Chain
Ice
Pick
Shelters
Wood
Stoves
Wall
Tents
Steambaths
Insulation
& Vapor Barriers
Gas
Lamps & Gas Stoves
Travel
Piloting
A Boat
Boat
Design
Magnetos
& Spark Plugs
Carburetors
Compression
Outboard
Motor Lower Unit
Outboard
Motor Cooling System
Dogsleds
Snowmachine
Tracks
Snowmachine
Clutch
Snowshoes
Winter
Trails
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Activities
- Put a weight on a string. Attach a strong rubber band or soft
bungee cord to the string. Hold the loose end of the rubber band
and spin the weight around the head. (The dangers of this should
be fairly obvious.) Try this with different weights and different
strengths of rubber bands. Can the students feel the difference?
The heavier weight will stretch the bungee more than the lighter
one. The greater the speed, the greater the stretching of the
bungee.
- If students haven’t tried the old water-bucket-around-the-head
activity, let them try it. This illustrates inertia quite well.
Fill a bucket about 1/4 full with water. Swing the bucket.
Why doesn’t the water come out of the bucket when it is upside
down? The inertia of the water in a straight line is greater than
gravity.
- There are two types of chainsaw clutches: those with the sprocket
on the outside of the clutch and those with the sprocket on the
inside. Find one of each kind in the village and draw a top view
of each.
- Do this outside. Get an experienced person to run a saw that
has the sprocket on the inside and clutch on the outside. Take
the cover off and observe the operation of the clutch. Increase
and decrease rpm. Can you see the shoes go in and out? Describe
what you see to someone who didn’t see the demonstration.
Be careful. One teacher did this and a student touched the
moving clutch and broke a finger.
- Look on the chainsaw in the above activity for the oil flow
adjustment. Observe the oil coming out of the saw to supply the
bar. Adjust the oil flow. Is the difference obvious? Find the
hole in the bar that allows the oil to flow to the chain. Is there
a similar hole if the bar is turned over?
- Get a chainsaw clutch from an old chainsaw. Look at the drum.
Does it look blue from being overheated? Look at the shoes. Test
them for friction with other materials. Do they look like they
are made of high friction material? What do you think that material
is? To get the clutch off you will probably have to follow these
directions:
- Remove the sparkplug.
- Put a screwdriver in the sparkplug hole and turn the engine
until you feel the piston is at the bottom of the cylinder.
Remove the screwdriver.
- Cram the cylinder full of nylon or other plastic rope.
Now you can put a wrench on the nut holding the clutch and
the rope will hold the crankshaft from turning.
- Test the clutch spring for tension. Is it a strong spring?
Does it also look blue from overheating? Does it stretch evenly
or is it dysfunctional?
It is a very strong spring.
- Imagine what would happen if oil got into the clutch. What
problems do you think would occur if this happened when the saw
was operating?
The oil would reduce the friction between the drum and shoes.
The clutch would slip.
- Get some 30w oil. Heat it by putting the plastic container
in very hot water. How thin does it get? Do you think it would
stay on the bar well when it is that thin? Cool it in a freezer.
Feel it. Do you think it would pump well at this temperature?
At cold temperatures oil has a hard time to flow.
- Get some commercial bar oil. Put a little on your fingers.
How is it different from regular 30w oil? Why do you think this
is so?
Commercial bar oil is actually sticky. It is intentionally
so to allow it to stick to the chain and bar, and not floy off
the end of the bar.
- Get some crankcase oil. Wrap a magnet in thin plastic wrap.
Immerse the tip of the magnet in the old oil and see if you can
pick up the iron filings that are supposedly in the crankcase
oil.
- Get a chainsaw bar with a roller nose. Does it have a hole to
grease, or is it permanently lubricated?
Some do, some don’t. if it has a hole to lubricate and
you ignore it, the nose will spoil in a short time.
- Get several bars and chains, new and old. Test them for side
motion and wear. How sloppy is the chain in the bar? Does it tend
more towards one side than another? Which part of the bar is worn
the most? Does it look like the owners turned the bar over often,
or is one side worn more than the other?
The comparison between new and old bars should be obvious.
- Draw or trace a side view of a chainsaw chain.
- Ask people in your village what is the best saw they ever owned
and why. What is the favorite bar length?
This varies from town to town.
- Ask people in the village how they cut wood before chainsaws.
If you can, fall and buck a tree using that method.
We used swede or two man saws. This was quite slow and tedious.
- Ask people in the village the names of the chainsaws they know
or remember. Make a class list. Find on the map the locations
where they were manufactured.(You will need a world map.)
A good chance to slip a little geography into the scienc class.
- Ask in the village if someone can demonstrate how to splice
a broken chainsaw chain.
You will need to order extra links ahead of time. The links
should match the chain, 3/8 or .404 pitch.
- Gently file the materials of the bar, clutch drum, clutch shoes,
sprocket, chain dogs, and teeth. Which are hard and which are
softer than a file?
- Have a contest to see who can untangle a chainsaw chain the
fastest. (This is often a challenge!) Let students tangle a chain,
and pass it to the next person to untangle.
- Get an owner’s manual. Draw a picture of two dangerous
activities that should be avoided.
There is nothing safe about chainsaw operation, yet young
Alaskans handle them all the time. This lesson is a good opportunity
to teach safety that will prevent future accidents.
Student Response
- What might happen if the chain and engine of a chainsaw were
always connected?
It would be dangerous and hard to start
- What are the two main parts of the clutch?
The drum and the shoes wrapped with a spring
- How does inertia work in a chainsaw clutch? The shoes are held
in tightly to the driveshaft by a strong spring. When the speed
of the engine gets high enough, the shoes spread out against the
tension of the spring. The law of inertia says a body in motion
will stay in motion in a straight line. The shoes, in response
to this, expand out tight against the drum that drives the chain.
(Exact wording is not necessary or likely.)
- What is around the shoes that keeps them from flying outward
at low rpm? What would result if it were too loose? Too tight?
A spring. If it is too loose, the clutch engages at too low
an rpm. If it is too tight, the engine has to turn very fast to
allow the shoes to overpower the spring and engage the drum.
- Draw a chainsaw clutch where the engine is turning at low rpm
and the chain isn’t turning.
- Draw a chainsaw clutch where the engine is turning at high
rpm and the chain is turning.
- If there were low friction between the shoes and drum, what
would happen when there was a load on the chain?
The clutch would slip. The chain would stop even if the engine
were turning.
- What happens to the shoes when the engine is slowed down after
running at high speed?
They retract back to the center, pulled in by the spring.
- What is happening when the chain is stuck in the tree and the
saw is being run at high rpm?
The shoes are slipping against the drum. The heat from the
friction can warp the drum.
- What happens when chain oil is too thin? Explain or draw it.
The oil flies off the end of the bar and doesn’t make it
around to the pressure/contact points where the cutting is being
done.
- What happens if the chain oil is too thick?
It can’t get through the oil pump and a shortage of oil
on the bar results.
- How is professional bar oil different from 30w oil?
It is sticky
- Why is the use of old crankcase oil discouraged?
It has iron filings that can greatly wear the bar and chain.
- What is a roller nose on a chainsaw bar? What is the purpose?
A roller nose on the end of the bar has bearings that reduce friction
on the nose of the bar.
- Draw a chainsaw bar and chain as they are cutting a block. Identify
the place on the bar where the chain is loose. Identify where
it is tight.
Math
- Commercial bar oil is $3 per quart. Henry bought eight quarts
and figured that his bar lasted two times longer than if he used
free crankcase oil. A new bar is $30. Did he save money?
Yes. The bar oil cost $24, a new bar would cost $30.
- Would it be cheaper if he ordered an extra bar from a discount
place for $22 or commercial bar oil for $2.25?
Yes, it is still cheaper. The bar oil would be $18 and the
bar $22.
- Henry can get bar oil for $3 a quart, or order in bulk, 5 gallons
for $32, plus $13 shipping. Is he saving money, and if so, how
much? The answer can refer to quarts or 5-gallon buckets.
The cost by quarts is $60. The total cost for bulk is $45.
The savings is $15 per 5-gallon bucket or $.75 per quart.
- Jesse wants to sell cordwood. He figures that each cord for
his chainsaw takes 1 quart of bar oil at $2.75, 3/4 gallon of
gas at $3.50 per gallon including two-cycle oil. Snowmachine costs
are about $21 per cord, including wear and tear. It takes 5 hours
to cut and haul a cord. How much should he charge to make the
equivalent of $10 per hour? $12 per hour?
His overhead per cord is $26.37 if he makes $10 per hour, his
labor costs are $50. He must charge at least $77 per cord to make
$10 per hour. If he wants to make $12 per hour he has to charge
$87.
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