as comfortably possible. This will put the blade in
the proper operating range.
SCALE ON WORKPIECE
All hot rolled materials will have a degree of mill
Machines with hydraulic blade tension control can
scale. On low carbon mild steels this scale is
in most cases be adjusted to over-tension a blade.
negligible as far as cutting rates are concerned, but
As a starting point, we recommend checking the
it shortens the blade life. When structurals, angles,
hydraulic diagram for the recommended pressure
etc. are being cut, the ratio of exterior area to the
adjustment. On average sized work pieces this will
cross section area is very high, resulting in extreme
be adequate tension for good cutting and good
abrasion to the blade and consequent shorter blade
When cutting large material with wide blade spans,
On alloy steels this mill scale can be very
the blade tension may have to be increased to
detrimental to the band saw blade and we definitely
obtain maximum blade stability. Because the
recommend it be removed prior to the cut. Some
maximum allowable tension varies from blade
scales are so hard and abrasive that they must be
types and manufacturers, the best procedure is to
removed in order to successfully cut the materials.
check with the blade manufacturer for the
maximum allowable tension of the blade being
used. This tension can then be applied and used as a
Hard surfaces can be created on a work piece by a
good starting point.
wide variety of operations. The following are a few
of the more common problems encountered:
Another method may also be used in the absence of
CUTTING WITH A TORCH can create a
any available information. Keep a record of the
"case hardened" area if an excess of acetylene
running time on the saw blade until it breaks. Then
is used to make the cut. While this shell is only
increase the blade tension 10% each time a new
a few thousandths of an inch thick, cutting
blade is installed until the blade breaks before it
through it with a band saw blade will dull the
wears out. This will then be the maximum tension
teeth, creating extreme problems.
point. Reduce the tension 15% below this point and
operate the blades long enough to see if the average
GROUND SURFACES -- on some high carbon
blade life is used before the blade breaks.
and die steels, improper grinding practices can
result in the hardening of the surface.
When this point is reached, the blade will be
operating at its maximum practical beam strength.
HARD SPOTS IN THE WORK PIECE
Let us again call to your attention that this is
Some welded seam tubing will have a hard zone by
normally only necessary when large machines are
the welded area if it is not properly annealed. This
sawing near capacity work.
hard section can at times be too hard to cut.
For most applications and blades, the tension range
Some die steels may have inclusions of slag or scale
given on the hydraulic diagram or manual will
within the block. These inclusions are as hard as the
result in adequate tension and good cutting. Some
teeth on the blade, and will dull the teeth as the
machines show the proper hydraulic pressure
blade cuts through them. This in turn will cause the
setting on the blade tension gauge by setting the
blade to start cutting crooked.
gauge needle to a green dot on the dial.
16. BLADE TENSION
As a general guide line, the higher the blade ten-
sion, the sooner the blade will fail and break due to
running stress and tension. However, as the blade
tension is increased, the accuracy of cut also in-
creases. This means that a tension must be used
that is high enough for accurate cutting, but not
high enough to shorten blade life.
Machines that are equipped with manual hand
knobs for blade tensioning have knobs sized so one
can generally tighten them with one hand as tight