The American
Heritage® Dictionary of the English Language: Fourth Edition. 2000.
Background
“The saw was one of the
first great innovations of the Metal Age. It was
developed with smelted copper, from which a blade could
be cast. Many of the early copper saws have the general
appearance of large meat-carving knives. Egyptian
illustrations from about 1500 BC onward show the saw
being used to rip boards, the timber being lashed to a
vertical post set into the ground.
Though there is no
evidence of the type of saw used, Egyptians were able to
saw hard stone. The blade, was probably toothless, and
rode on an abrasive material such as moistened quartz
sand. The 7 1/2-foot granite coffer still in the Great
Pyramid carries saw marks.
During the Bronze Age,
saws became much more widespread in woodworking. It was
in this time that the modern form of the saw began to
come into play. Some of the saws used resembled hacksaw
blades of today. Iron saws started to be produces in
the mid 7th century BC. The Romans, added many
improvements to simple says which made them easier to
work with. For example, they added a rib to the back of
saws to reduce the buckling of the thin blade. Hacksaws
today use similar ribs to those on the ancient Roman
saws“.
Hacksaw
“A saw is a tool for
cutting solid materials. Most saws take the form of a
thin metal strip with teeth on one edge or a thin metal
disk with teeth on the sides pointing outwards. The
teeth are usually bent to alternate sides so that the
groove cut by the saw is wider than the thickness of the
saw. This prevents binding between the cut surfaces and
the sides of the saw. The thin-strip saws are used in a
variety of arrangements for both hand and machine
operation.
The hacksaw consists of three parts: the frame, the
handle, and the saw blade (Figure below). Frames are
either the solid or adjustable type. The solid frame can
only be used with one length of saw blade. The
adjustable frame can be used with hacksaw blades from 8
to 12 in. in length. The blade can be mounted to cut in
line with the frame or at a right angle to the frame.
When the distance to be sawed is greater than the space
between the blade and the frame, it may be necessary to
set the blade at 90 degrees as in so the work can clear
the frame.
Most hacksaw blades are made from high speed steel, and
in standard lengths of 8, 10, and 12 in. Blade length is
the distance between the centers of the holes at each
end. Hand hacksaw blades are generally 0.5“ wide and
.025“ thick. Modern day saw blades are taper ground
which means that the back end of the blade is thinner
than the side with teeth. The kerf or cut produced by
the hacksaw is wider than the .025 in. thickness of the
blade because of the set of the teeth.
Hacksaw use
The saw blade may break
if it is too loose in the frame or if the work piece
slips in the vise while sawing. Too much pressure may
also cause the blade to break. A badly worn blade will
cut a too narrow a kerf, which will cause binding and
perhaps breakage of the blade. When this happens use a
new blade to finish the cut. Make sure that the cutting
is done close to the vise jaws for a rigid setup free of
chatter (but not so close that you cut the vise). Work
should be positioned in a vise so that the saw cut is
vertical. This makes it easier for the saw to follow a
straight line. At the end of a saw cut, just before the
pieces are completely parted, reduce the cutting
pressure or you may be caught off balance when the
pieces come apart and cut your hands on the sharp edges
of the work piece. While sawing stand as close to the
vise or work piece as is comfortable, with your feet
slightly apart to provide stability. If possible, the
work piece and your elbow should be at about the same
level. To saw thin material, sandwich it between two
pieces of wood for a straight cut. Avoid bending the saw
blades because they are likely to break, and when they
do, they usually shatter in all directions and could
injure you or others nearby.”
By the
way
Bi-metal blade is
suitable for cutting all types of materials. The
teeth are made of 8% cobalt and 10% molybdenum. The
tooth forms are specially designed to get best
performance.
While cutting HARD
MATERIALS you need a larger number of teeth than
soft materials.
While cutting thin
section the teeth must not straddle the material at
least three consecutive teeth must always be in
contact with the material.