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Material Hardness.
When choosing the blade with the proper pitch,
one factor you should consider is the hardness
of the material that is being cut: the harder the
material, the finer the pitch that is required. For
example, exotic hardwoods such as ebony and
rosewood require blades with a finer pitch than
American hardwoods such as oak or maple.
Soft wood such as pine will quickly clog the
blade, decreasing its ability to cut. Having a
variety of tooth configurations in the same width
will most likely give you an acceptable choice
for a particular job. There are certain things that
indicate if a blade has a proper pitch, too fine a
pitch or too coarse a pitch.
Some are listed below:
Proper Pitch
Blades cut quickly.
A minimum amount of heat is created when the
blade cuts.
Minimum feeding pressure is required.
Minimum horsepower is required.
The blade makes quality cuts for a long period.
Pitch Is Too Fine
The blade cuts slowly.
There is excessive heat, which causes
premature breakage or rapid dulling.
Unnecessarily high feeding pressure is
required.
Unnecessarily high horsepower is required.
The blade wears excessively.
Pitch Is Too Coarse
The blade has a short cutting life.
The teeth wear excessively.
The bandsaw vibrates.
Width
The dimension from the back of the blade to the
front of the teeth. The wider the blade, the
stiffer the blade and the straighter the cut. This
is usually called beam strength. But wide
blades cannot cut small radiuses.
The narrower the blade, the more flexible the
blade and the greater the tendency the blade
has to wander. These have low-beam strength,
but can cut small radiuses. Blades are
available from 3mm up for your machine.
Kerf
The width of the saw cut. The larger the kerf,
the smaller the radius that can be cut, the
greater the amount of wood the blade has to be
removed by the blade and the greater the
horse power that is needed because the blade
is doing more work. The greater the kerf, the
larger the amount of wood that is being wasted
by the cut.
Hook or Rake
The cutting angle or shape of the tooth. The
greater the angle, the more aggressive the
tooth and the faster the cut. But the faster
the cut, the faster the tooth will blunt, and
the poorer will be the surface finish the cut
will have. Aggressive blades are suitable
for soft woods but will not last when cutting
hard woods. The smaller the angle, the less
aggressive the tooth, the slower the cut and
the harder must be the wood that the blade is
suitable to cut. Hook teeth have a progressive
cutting angle and take the form of a progressive
radius. They are used for fast cutting where
finish is not important. Rake teeth have a flat
cutting angle and are used for a fine surface
finish of the cut.
Gullet
The area in which the sawdust has to be
transported through the wood, the larger the
tooth (pitch) the bigger the gullet is.
Relief
The angle from the tip of the tooth back. The
greater the angle, the more aggressive
the tooth but the weaker the tooth.
Beam Strength
This is the ability of the blade to resist bending
backwards. The wider the blade, the stronger
the beam strength; therefore, a 25mm blade
has far greater beam strength than a 3mm
blade and will cut straighter and is more
suitable for resawing.
Blade Selection
As you have seen from the previous section,
there are a great number of variables. The
blade selection that you will make will greatly
depend on the type of work that you intend to
do with your machine. If you have experience
with the bandsaw, you will probably have a
good idea of the blades that are suitable for
you. If you lack the experience or are unsure
of the type of work you will be doing with your
machine, we recommend that you purchase a
selection similar to that listed below, which is
a good general selection and will allow you to
tackle most jobs. As you gain experience, you
will settle on the blades that suit you.
1. 6 mm x 6 TPI. This is a small, aggressive
blade that is suitable for tight curves and fast
cutting where a good surface finish of the cut is
not important.
2. 6 mm x 14 TPI. This is a small, fine blade
suitable for reasonably tight cuts where the
surface finish is important but speed of cut is
less important.
3. 13 mm x 3 TPI. This is a general-purpose
blade that can cut large radiuses and short
sections of straight cuts. The cut is fast but the
surface finish of the cut is poor.
4. 19 mm x 3 TPI. This is a general-purpose
blade, which will be used for straight cuts and is
suitable for large radiuses.
5. 25 mm x 2 TPI. This is a resaw blade, which
will be used for straight cuts and is suitable for
processing veneers.
Rounding the back of the blade
With most guide systems it is recommended
that the back of the blade be rounded with a
stone. As the machine is supplied with Laguna
ceramic guides, this is not imperative because
the ceramic will round the back of the blade as
it is used. However, if you decide that you want
to round the back of the blade, a procedure
follows.
A round blade back creates smooth interaction
between the thrust bearing and the blade. If the
blade rotates slightly, there is no sharp blade
corner to dig into the thrust bearing; also, the
rounding process smoothes the weld. A blade
with a round back makes tight turns better
because the round back has smooth interaction
with saw kerfs.
After the guides have been adjusted and the
machine is running, hold the stone against the
back corner of the blade for about a minute.
Wear safety glasses when rounding the blade.
Then, do the same thing on the opposite
corner. Next, slowly move the stone to round
the back. The more pressure you put on the
back, the faster you will remove the metal. Be
careful that the inside of the machine is free of
sawdust because sparks could start a fire. On
small blades such as a 1/4“ blade, the pressure
on the back of the blade may bring the blade
forward off the front of the wheels. Therefore,
be careful not to put too much pressure on the
stone. When doing this, it is also important that
the upper guides be positioned right above
the stone.
The blade has teeth and extreme caution
must be exercised, as your hands will
be very close to them.
Causes of blade breakage
1.
Excessive blade thickness in relation to the
flywheel diameter.
2.
Defective welding.
3.
Incorrect tension, particularly if the blade is
over tensioned; the tension spring no longer
fulfils its function.
4.
After use it is recommended that you slacken
the tension, especially overnight. (Be sure to
place a clearly visible note on the machine that
you have done this.
5.
Misalignment of the flywheels.
6.
Irregularity of flywheel surface, for instance,
an accumulation of sawdust while cutting
resinous materials.
You can correct these problems by readjusting
the machine, changing the way you operate it
or by changing the blade. Try only one change
at a time.
Causes of blade dulling.
1. Poorly set side guides or rear thrust guide.
2. Poor tracking.
3. Wrong blade selection. If the blade is too
narrow, it will flex more easily and decrease the
quality of the cut. The blade should also have
the correct pitch and width.
4. The tooth pitch is too fine (too many teeth per
inch).
5. Certain woods will dull a steel blade very
quickly, especially tropical hardwoods (teak,
koa, etc.). Other woods with a high silicon
content will also dull the blade quickly; even a
cut as short as 152,4mm will cause damage to
the blade.
6. On certain exotic woods, the ends have been
painted. This is done to control the drying.
The paint is very abrasive and will dull the blade
as you cut through it. It is recommended that
you cut the painted ends off your wood.
Using a radius chart.
Until you become well acquainted with your
saw, it is best to use the contour (radius) chart
to determine which size blade to use for a
specific application. Radius charts can be found
in many woodworking books, magazine articles
and on blade boxes. They differ slightly from
one another but are good as rough indicators of
how tightly a curve can be cut with a particular
blade. Each blade saw and operator is different,
so it is impossible to make a truly accurate
chart. A blade can cut continuously without
backtracking any curve that has a radius as
much as or more than is shown on the chart.
For example: a 3/16“ blade will cut a circle with
a 5/16“ radius or a 5/8“ diameter. To test if a
3/16“ blade would work for a particular curve,
place a dime (roughly 5/8“) over the pattern.
The 3/16“ blade can cut a curve bigger than the
dime, but not smaller. You can use everyday
items such as coins or a pencil to determine
which blade to use. A quarter is the size of the
tightest cut that can be made with a 1/4“ blade.
A dime is the size of the tightest curve that can
be cut with a 3/16“ blade. A pencil eraser is the
size of the tightest turn that you can make with
a 1/8“ blade. After a while you won‘t even need
an object to size the possible curve of a blade
because you will have become familiar with this
process. There are options to matching the
blade to the smallest curve pattern. If there is
only one very tight cut, it may be best to use a
