Saw Smith at Work

Saw Smith at Work
By
Edward J. Gierl
and
Ann Marie Gierl
Edward Gierl lived in central Wisconsin where he had a saw mill and farm.
Eventually he moved on to smithing and filing saws as his career.
Dedication
This treatise is written at the request of friends who appreciated improved
efficiency with their lumber-cutting sawmills after their circular blades were first
improved by smithing.
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Introduction
Smithing is the art of correcting the tension and surface profile of the circular
mill saw. Circular saws change their profile and tension as they cut. This in turn
influences how effectively they saw. The amount of dishing or depth of profile a saw
has matters much. Saws may be warped by overuse or misuse. For example, they
may cut badly due to heating up and expanding from being run too fast on the saw
mill. If the tension and dishing of a saw is done incorrectly or poorly it will not saw
lumber well. These are problems that a good saw smith can improve.
Smithing is learned over time. It is done by hammering a saw after first
finding and marking the spots to be hit. Gradually you will learn the feel of the
hammer on the saw, sense the saw’s spring and easily see the dishing or high spots
to pound out.
Key Points and Terms
Tension can best be described as pressure in the inner saw blade. Why does
tension matter? Tension is needed to hold the saw’s shape while cutting lumber.
The faster a saw is turned, the more the saw is pulled outward by centripetal force.
Good tension in the saw keeps it held inward so boards are cut straight.
Tension is changed in the circular saw by hammering it in specific areas after
using a tension gauge to identify areas that need correcting. Hammer blows expand
the saw plate in the spots hit, resulting in the metal being compressed and spread.
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The gradual hammering of a saw to even out high spots and to create tension makes
a saw run smoothly and cut the log with minimal error or waste.
The saw area being hammered lays flat on a hard (iron) anvil. To pound
tension into a saw, one starts in the center and works outward guided by the tension
gauge. To pound tension out, one starts at the outer rim and works inward guided
by the tension gauge.
Mill saws that run at 800 RPM need more tension than slow-running saws.
Saws that run at slow speeds (300-500 RPM) and smaller saws with diameters less
than three feet (one meter) can cut straight without much tension. Saws must be
fitted for tension to the individual mill.
The ‘board side’ of the saw faces the board being cut. The ‘log side’ faces the
remaining log yet to be cut. The saw should be flatter on the log side.
A right hand saw mill has the log on the right side of the saw and a left hand
mill has the log on the left side of the saw when cutting a board.
Other factors also keep saws running well. The saw heats up and expands
with use because heat from the bearings near the shaft gets transferred to the arbor
hole collar. This expands the center of the saw resulting in dishing of the saw. A
crooked saw cuts crooked boards. Keeping bearings in good repair is essential.
Wooden saw guides on both sides of the saw’s front cutting edge are essential to
keep the saw in line to assure straight cutting. Tooth arrangement and sharpening
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are also very important for optimal sawing. These factors will not be discussed in
this monograph.
Necessary tools for smithing
First you must have the smithery, an area where you can set up an anvil and
hammering table. You also need ear protection, because hammering is loud.
A proper hard-surfaced anvil is needed. It should be mounted at about waist
height on the hammering table or on a sturdy upright post securely attached to the
hammering table.
A hammering table should have a wide movable top to lay the saw flat, a
center cone where the arbor hole fits, and casters or pins to carry the saw around.
The casters should be located under the rim of the saw when it is on the cone. (See
model below and design on the last page.)
Anvil
Center peg / cone
Vertical peg
Movable top
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Tension gauge
Center cone
Saw
Table
Casters under the saw
Anvil
The far end of the table should be
adjustable up and down to assure full flat
contact of the saw blade with anvil before
the saw smith drops the hammer.
A mounted peg extending horizontally
close to the anvil allows for vertical hanging
of the saw through the arbor hole when checking for high spots to be leveled.
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Saw hammering is done with a round nose hammer for round spots and a long-face
or cross-face hammer for longer spots. The hammer should weigh about 3-5 pounds or
2.5 kilograms.
A straight edge is needed to find out what areas of the saw are level. Use a
size that you can easily move along the saw but is long enough to span at least 1/3 of
the saw’s diameter. It can be as small as 6 inches long for a small saw to almost 30
inches in length when used for large circular saws. A longer straight edge can be
helpful to see the saw’s profile, such as when it is held vertically on the peg.
straightedge on saw
A long tubular light, such
as a fluorescent light, is used to cast light so you can view light passing under the
straightedge. High spots that need hammering have no light underneath. Low spots have
light showing, identifying where the saw is uneven and may need correction from the
other side.
A thin cardboard about 1-2 millimeters thick (such as a shoe box cardboard)
is sometimes needed to cover the anvil. It is placed over the anvil while doing gentle
hammering of high spots and when working around arbor and pin holes to avoid
thinning those areas. The saw should always be thicker around the arbor hole in the
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saw center. Hammering too hard on that area may spread the metal too much and
change the shape of the hole.
Smithing
Smithing involves finding and hammering out uneven spots on a circular saw
and correcting tension so the saw cuts well.
Start by hanging the mill
saw vertically on the peg. You
may want to wear gloves to
protect your hands from the
saw teeth when lifting the saw.
Mark a line with chalk (or an
erasable marker) from a top
gullet down to the arbor hole.
Do this the same on both sides. Maintain this line until you finish.
Practice holding the chalk and straight edge. Below is the best hand position
for holding the chalk and
straight edge that worked for
me. You could also hold the
chalk in one hand and straight
edge in the other hand. You
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might have to change holds on your tools at times. Learn the best way for you.
Chalk is used so the spots can
eventually be rubbed off when
done treating them.
View from other side of
3rd and 4th fingers
Now you start the essential first part of smithing. Adjust a tubular light on the
far side of the saw. Hold a straight edge across the saw. Look for a high spot that
touches the straight edge and casts a shadow on the saw. The light beam gleams
under the sides of the straight edge around the high (shadowed) spot. Mark the
high spot with chalk.
Continue to use the straightedge to find high or uneven areas of the circular
saw. When you find them
use chalk to mark several
of them. Mark small
areas with “x” or “o” and
the longer areas with
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lines. The line you drew from edge to center helps you know if you have assessed
the whole saw. Also notice any bad dishing or warping of the saw when it is hung on
the side of the hammering bench.
After some spots are marked you will begin hammering the areas needing
adjustment. First put on hearing protection to block out the loud noise of the
hammer.
Lift the saw back to a horizontal position on the top of the saw bench. Set the
saw down flat onto the padded anvil. Recall that each spot to be hammered must
have the saw plate fully flat on the anvil. Hammer only on the spot directly on the
anvil.
Some smiths first “feel” with a light tap or two each time, checking for solid
contact before they drop the hammer. Recall that you use a round nose hammer for
round spots, long-face or cross-face hammer for longer spots.
Now take the hammer and
pound down on your first
marked spot. Hit accurately and
not too hard to get a feeling for
the correct thud on that saw.
Shift and guide the saw over the anvil carefully before each tap so that you are
always hammering on the anvil. Start with a half dozen of the worst high spots.
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Start pounding gently. If you hit too hard you’ll pound through and make a big dent
to pound back from other side. Get the feel of your hammer and saw.
You have already found some of the saw’s worst high spots. Now you can
start looking in more detail. Place the saw vertical again on the peg. You, the saw
smith, will again glide the straight-edge across the saw’s illuminated surface looking
for some high places that need attention. View the old marks and make new marks
on the most noticeable spots as needed until you
get to the last turn. By rocking your straightedge
you may find some additional high spots to mark
that are made more visible by the light beam.
Continue this until you have checked the whole
first side of the saw.
Gleam of light under the straightedge indicates a
low spot
Place the saw back on the table and
hammer one segment at a time, rotating the saw as you go around. Always keep the
spot you are pounding directly on the anvil. Remember that if you pound too hard
you will have to correct your mistake on the other side. It is better to do a little at a
time. If the saw’s steel is quite hard you could dish it if hitting too hard.
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You’re pounding your first saw! After hammering some of the worst high
spots on one side you will next need to flip the saw over to mark and hammer some
on the other side.
When you have hammered all the spots marked, again lift the saw off the table
and hang it vertically on the side peg. Look once more for high spots. Check to see if
the saw changed any since you started. It may be better! Note if some spots that
you pounded on the first side went through the back side. Keep trying. Do you see
more spots, even some that you marked before? Place the saw back on the table
and, with the pad on the anvil, tap out the high spots. Normally you will need to flip
the saw and work side to side a half dozen times to get the dents out and level the
high spots.
Employing the Tension Gauge
The adjustable tension gauge is a precise instrument to determine the amount
of dishing needed in a circular saw. Too much dishing means the saw has too much
tension. A saw that is too flat needs more tension.
Tension gauges have a movable metal bottom edge attached to a metal top
piece. It is possible to buy or make a tension gauge.
The first set of drawings below show how a tension gauge is put together so
you can make one yourself if needed.
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A manufactured metal tension gauge, also pictured below, is similar to the
hand drawing but may be hard to find or buy.
The pressure sensitive Allen tension gauge is also likely available and may be
readily purchased.
In all these gauges the base moves very slightly, measuring the degree of
depression or dishing in the saw. This measures of the saw’s tension and allows the
saw smith to hammer the saw to expand or contract the steel so the tension can be
optimized.
The gauge in this drawing is 21 inches in length.
The movable bottom edge is attached by 2 bolts near the ends. It has a center
‘gauge’ which is essentially a steel wedge that pushes down the bottom edge to
measure the saw’s concavity.
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On the back is a brace so it can be balanced over an area,
as in the side view drawing.
Brace
Below is a metal tension gauge with steel wedge that pushes down the bottom
edge to measure the saw’s concavity.
http://www.oldengine.org/members/jdunmyer/sawmill/may29_05.jpg
Gauges that measure the tension by pressure such as the Allen Tension Gauge
(pictured below) are also options. By applying pressure on the gauge, an exact
curve is measured which provides guidance to set tension (the drop) in the saw. A
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chart accompanying the gauge relates the circle diameter to the drop measured
(needed) on the gauge’s dial.
http://www.thinkerf.com/AllenGauge.htm
Tension gauges are used to establish the saw’s rim. The rim is important: it
must retain the tension within the saw and contain the centrifugal force from speed.
The rim runs from the base of the saw teeth gullets inward. For an inserted tooth
saw it starts just below the shank.
Larger saws get a wider rim. Large saws run faster and need more tension. As
large saws are run they heat up more, especially under poor sawing conditions such
as if the saw teeth are dull or if the saw is pinching or binding due to cutting through
hard timber. Heat expands the saw and changes the tension.
The tension gauge, when pressed down, measures the curve of the saw. The
degree of curving can be too much or too little. The smith decides how much the
saw should be hammered to expand or contract, thus setting the tension. A
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depression of maybe several millimeters (1/16th to 1/4th of an inch) over the
radius of the saw is a typical amount of tension needed for a large saw (41 to 56
inches).
As in this drawing, the top saw is badly dished. It has too much tension. The
bottom saw has the right amount
of curve or tension if it matches
the bottom metal edge of the
tension gauge as set by the saw
smith.
Typically the saw’s tension can be considered when you first size up the saw. This
is done by taking a straight edge about 1/3rd the width of the saw and holding it near the
center and along the radius of the saw. Rock it back and forth. Is the saw stiff and has no
curvature? If so it may need slight tensioning before hammering out the high spots when
smithing. If the straight edge wobbles some then the saw has enough tension to start
leveling. Checking tension and leveling the saw are often done interchangably when
smithing a saw.
The best technique for tensioning a saw is to use a light beam on the far side of the
saw, shining light on the saw while holding the tension gauge (similar to the technique
used when finding the high spots to level in the first segment of this paper). You will
look to see if light comes under or around the tension gauge. If there is no light then the
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saw’s tension matches what was set by the saw smith. If there are high or low spots you
will see a gleam of light under or around the tension gauge.
To check tension you will need to be at eye level with the saw and the tension
gauge. Place the saw horizontal as pictured below. Place a flat wooden block
crosswise on the far end of the table so you have something to rest the far end of the
saw on when you lift the other end.
Check on the tension by holding the tension gauge and rocking it slowly back
and forth along the radius of the saw. Do you see high spots? Find and mark 3-6
high spots. Pull the saw around a little. Check the tension at about every other
tooth gullet. Mark from the outer most to inner most bumps.
Hand holding tension gauge
at the radius of the saw
Wooden block. You may
also want to add a block on
the near end to help hold up
heavy saws.
Once again mark high areas with chalk, leveling these areas that may need a
change in tension. Go around 1/6th of a turn. Go past the center hole, across the full
saw. Before hammering these spots, adjust the height on the back end of the table so
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the saw lays flat on the anvil for good contact when the smith drops the hammer.
Pad the anvil to avoid pounding too hard (which spreads the saw too much). If
there are large bumps to pound out also use a pad. Next flip the saw to lay it flat and
again check for bumps. Go around 1/6th of a turn. Repeat until you have checked
and marked areas on the whole saw .
To pound tension into a saw, start pounding at the inner 1/4 to 1/3 saw
region and working outward from the center. To pound tension out of a saw, start
at the outside perimeter of the saw and pound toward the inner half of the saw.
Sometimes a saw might be so stiff that you should do more treatment on the
same side. If so, vary your chalk lines. You may need to alternate between vertical
and horizontal checking and fixing of the saw’s tension and hammering out high
points.
Recall these important points:
1) spreading the steel saw too much will change the desired tension;
2) tension can be checked with the saw hanging vertical on the peg or
horizontal on the hammering table;
3) a smith may go back and forth with checking and changing the tension
while leveling the saw, alternating between leveling with a straight edge and using
the tension gauge on a saw through the whole process of smithing.
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Checking the central collar area
The center area of the saw around the arbor hole and pin holes need careful
treatment. If hammered too much these holes can change shape and may not fit on
the saw mill. They are hammered with a pad on the anvil and only light taps of the
hammer.
Arbor hole
Shadow where there is excess concavity.
Place the tubular light crosswise at the far end of the saw table. Place the saw
horizontal on the hammering table. Lift the saw up to look for a drop in the saw.
Hold a straight-edge about 1/3 the length of the saw’s diameter. Halfway toward
the arbor hole press the straight edge of your tool down onto the saw plate,
edgewise and square across. Mark any spots that need leveling.
Carefully slide your straightedge toward the center and beyond it. By rocking
your straightedge you may find some spots that need tension correction. Mark a
half dozen of the worst high spots if any are found. Hammer the high spots found.
Rotate the saw, moving about 1/6th of the way each rotation, and repeat this.
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Important! When ready to hammer the areas close to the edges of arbor hole
or pin holes do not hit on a bare anvil. Slip some type of pad or cardboard under the
saw first. Hit lightly! If you hit too hard you might mushroom the edges of these
holes resulting in arbor and pins that can’t fit. These open edges bend easily!
Additional tips: When the saw is horizontal you should keep the saw
supported in the middle and edges. Casters or similar supports let you move the
saw around the hammering table yet keep it supported. Placing a circular wire or
similar round tube on the anvil under the saw near the teeth helps it roll but avoids
letting the saw teeth rub.
Points to remember:
When pounding the saw ask about the mill first. Is it for a right or left-hand
mill? The side of the saw facing the log should be straight. Ask what speed the saw
is run at. Guess if no one is sure. Record this and other pertinent facts. Recall that
faster run saws need more tension.
To pound tension into a saw, start pounding at the center 1/4th of the saw
and work outward. To pound tension out of a saw, start at the outside perimeter of
the saw. Leave a rim of several inches between where you pound and where the
teeth are located.
It is better to do things a little at a time. As you work on a saw it’s not
uncommon to find yourself varying your treatments of a problem saw – level and
tension, back and forth. You might have to treat each side of a saw five or more
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times before you see solid darkness under your tool with no uneven shadows. If you
hit too many spots at one time on one side of the saw it may become dished or
saucer-like. You shouldn’t expect it to be perfect right away. If a saw is stiff it needs
smithing to acquire some vibrancy.
Conclusion
Now you have the essential information to smith a circular saw. Smithing
correctly keeps the saw running well longer, resulting in straighter boards and less
wood lost. It takes time and experience to be a good saw smith. Keep at it until you
are sure the saws are running well with your improvements. Enjoy your work! It is
a hard task but can be done well. A good saw greatly improves the productivity of a
saw mill.
Things to know before you start smithing
1. When to use a bare or padded anvil.
a. A bare anvil results in more expansion of the saw when it is
hammered. If a saw has too much tension you can use a bare anvil
when pounding the outer 1/3rd or 1/4th of the saw. Keep
monitoring your progress by frequently assessing with the tension
gauge.
b. Keep a pad on the anvil:
i. when around edges of arbor or pin holes;
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ii. when pounding out dents;
iii. for center tensioning;
iv. if you want to avoid too much tension too soon.
2. The saw needs to be thicker in the center.
3. A large faster run saw needs to have more tension.
4. The saw should be straight on the log side after smithing.
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Hammering bench, as designed and used by Edward Gierl
Front view, anvil
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