Saw
From Wikipedia, the free
encyclopedia
A saw is a tool consisting of a hard blade, wire,
or chain
with a toothed edge. It is used to cut
through relatively hard material, most often wood. The cut is made by placing the
toothed edge against the material and moving it forcefully back and forth. This
force may be applied by hand, or powered
by steam,
water,
electricity
or other power source. An abrasive saw
has a powered circular blade designed to cut through metal.
Terminology
- Heel:
The end closest to the handle.
- Toe: The
end farthest from the handle.
- Front:
The side with the teeth (the "bottom edge").
- Back:
The side opposite the front (the "top edge").
- Teeth:
Small, sharp protrusions along the cutting side of the saw.
- Gullet:
The valley between the points of the teeth.
- Fleam:
The angle of the faces of the teeth relative to a line perpendicular to
the face of the saw.
- Rake:
The angle of the front face of the tooth relative to a line
perpendicular to the length of the saw. Teeth designed to cut with the
grain (ripping) are generally steeper than teeth designed to cut
across the grain (crosscutting)
- Points per inch
(25 mm): The most common measurement of the frequency of
teeth on a saw blade. It is taken by setting the tip (or point) of
one tooth at the zero point on a ruler, and then counting the number of
points between the zero mark and the one-inch mark, inclusive (that is,
including both the point at the zero mark and any point that lines up
precisely with the one-inch mark). There is always one more point per inch
than there are teeth per inch (e.g., a saw with 14 points per inch will
have 13 teeth per inch, and a saw with 10 points per inch will have 9
teeth per inch). Some saws do not have the same number of teeth per inch
throughout their entire length, but the vast majority do.
- Teeth per inch:
An alternative measurement of the frequency of teeth on a saw blade. Usually
abbreviated TPI, as in, "A blade consisting of 18TPI." [Compare points
per inch.]
- Kerf:
The width of a saw cut, which depends on several factors: the width of the
saw blade; the set of the blade's teeth; the amount of wobble
created during cutting; and the amount of material pulled out of the sides
of the cut. Although the term "kerf" is often used informally,
to refer simply to the width of the saw blade, or to the width of the set,
this can be misleading, because blades with the same thickness and set may
create different kerfs. For example, a too-thin blade can cause excessive
wobble, creating a wider-than-expected kerf. The kerf created by a given
blade can be changed by adjusting the set of its teeth with a tool called
a saw tooth setter.
- Set: The
degree to which the teeth are bent out sideways away from the blade,
usually in both directions. In most modern serrated saws, the teeth are
set, so that the kerf (the width of the cut) will be wider than the
blade itself. This allows the blade to move through the cut easily without
binding (getting stuck). The set may be different depending on the
kind of cut the saw is intended to make. For example, a rip saw
has a tooth set that is similar to the angle used on a chisel,
so that it rips or tears the material apart. A "flush-cutting
saw" has no set on one side, so that the saw can be laid flat on a
surface and cut along that surface without scratching it. The set of the
blade's teeth can be adjusted with a tool called a saw tooth setter.
- Abrasive saw: A saw that cuts with an abrasive disc or band, rather
than a serrated blade.
History
In ancient Egypt, saws made of
copper are documented as early as the Early Dynastic Period,
circa 3,100–2,686 BC.[1][page needed] Examples of saws and models of saws have been found in many
contexts throughout Egyptian history. Particularly useful are tomb wall
illustrations of carpenters at work that show sizes and the use of different
types. Egyptian saws were set with the teeth projecting only on one side,
rather than in the modern fashion with the more advantageous alternating set.
According to Chinese legend, the saw
was invented by Lu Ban.[2]
In Greek mythology, as recounted by Ovid,[3]
Talos, the nephew of Daedalus, invented the saw. In archeological reality, saws date back
to prehistory and most probably evolved from Neolithic
stone
or bone tools.
"[T]he identities of the axe, adz, chisel, and saw were clearly established more than 4,000 years
ago."[4]
Handmade
manufacture of saws
Until at least the mid-19th century,
saws were made laboriously by hand. The teeth were filed out individually, then
"set" by striking alternate teeth with a hammer against a
"stake" or small anvil. Due to risk of breaking teeth, beginners were
given saw set
pliers which set even more slowly.[5]
Pit
saws
A pit saw
was a two-person (traditionally "two-man") rip saw. In parts of early colonial North America, it was one of
the principal tools used in shipyards and other industries where water-powered sawmills
were not available. It was so-named because it was typically operated over a saw pit,
either at ground level or on trestles across which logs that were to be cut
into boards by the pit-saw were mounted. The pit saw was "a strong steel
cutting-plate, of great breadth, with large teeth, highly polished and
thoroughly wrought, some eight or ten feet in length"[6]
with either a handle on either end or a frame saw.
A pit-saw was also sometimes known as a whipsaw.[7]
It took 2-4 people to operate. A "pit-man" stood in the pit, a
"top-man" stood outside the pit, and they worked together to make
cuts, guide, guide the saw, and raise it.[8]
Pit-saw workers were among the most highly paid laborers in early colonial
North America.
Types
of saws
Hand
saws
Hand saws typically have a
relatively thick blade to make them stiff enough to cut through material. (The
pull stroke also reduces the amount of stiffness required.) Thin-bladed
handsaws are made stiff enough either by holding them in tension in a frame, or
by backing them with steel or brass (on account of which the latter are called
"back saws.") Some examples of hand saws are:
- Bow saw
or Buck saw:
a crosscut saw with the thin blade held in tension in a frame;
- Coping saw:
for cutting wood patterns;
- Crosscut saw: for cutting wood perpendicular to the grain;
- Frame saw
or "sash saw": In general any saw with a thin blade held in
tension by a frame, this term often specifically means the ripsaw
also called a whipsaw.
- Fret saw:
for cutting intricate wood patterns;
- Hacksaw:
a fine-toothed tempered blade under tension, for cutting metal, bone[citation needed], and
other hard materials;
- Japanese saw: a thin-bladed saw that cuts on the pull stroke;
- Pad saw
or "keyhole saw" or "jab saw": a narrow-bladed saw;
- Plywood saw: a fine-toothed saw (to reduce tearing), for cutting
plywood;
- Rip saw:
for cutting wood along the grain;
- Turning saw:
a frame saw with a narrow blade used for cutting curves, larger than a
coping saw.
- Two-man saw:a general term for a large crosscut saw or rip saw
for cutting large logs or trees;
- Veneer saw:
a two-edged saw with fine teeth for cutting veneer;
- Whipsaw
or pit saw: a kind of rip saw
for cutting logs into lumber;
- Wire saw:
a toothed or coarse cable or wire wrapped around the material and pulled
back and forth.
Back
saws
"Back saws," so called
because they have a thinner blade backed with steel or brass to maintain
rigidity, are a subset of hand saws. Back saws have different names depending
on the length of the blade. Some examples are:
- Miter saw:
for making accurate crosscuts and miters in a workpiece
- Tenon saw
or "dovetail
saw" or "sash saw": for
doing precision cutting in woodworking.
Mechanically
powered saws
Circular-blade
saws
- Circular saw: a saw with a circular blade which spins. Circular saws
can be large for use in a mill or hand held up to 24" blades and
different designs cut almost any kind of material including wood, stone,
brick, plastic, etc.
- Table saw:
a saw with a circular blade rising through a slot in a table. If it has a
direct-drive blade small enough to set on a workbench, it is called a
"workbench saw." If set on steel legs, it is called a
"contractor's saw." A heavier, more precise and powerful
version, driven by several belts, with an enclosed base stand, is called a
"cabinet saw." A newer version, combining the lighter-weight
mechanism of a contractor's saw with the enclosed base stand of a cabinet
saw, is called a "hybrid saw."
- Radial arm saw: a versatile machine, mainly for cross-cutting. The
blade is pulled on a guide arm through a piece of wood that is held
stationary on the saw's table.
- Rotary saw
or "spiral-cut saw" or "RotoZip": for making accurate
cuts, without using a pilot hole, in wallboard, plywood, and other thin
materials.
- Electric miter saw or "chop saw," or "cut-off saw" or
"power miter box": for making accurate cross cuts and miter
cuts. The basic version has a circular blade fixed at a 90° angle to the
vertical. A "compound miter saw" has a blade that can be
adjusted to other angles. A "sliding compound miter saw" has a
blade that can be pulled through the work, in an action similar to that of
a radial-arm saw, which provides more capacity for cutting wider
workpieces.
- Concrete saw: (usually powered by an internal combustion engine and
fitted with a Diamond Blade) for cutting concrete or asphalt pavement.
- Abrasive saw: a circular or reciprocating saw with an abrasive disc
rather than a toothed blade, for cutting very hard materials such as
metal.
- Pendulum saw or "swing saw": a saw hung on a swinging arm, for the rough cross cutting of wood in a sawmill
and for cutting ice out of a frozen
river.
Reciprocating
blade saws
- Jigsaw or
"saber saw" (US): narrow-bladed saw, for cutting irregular
shapes. (Also an old term for what is now more commonly called a
"scroll saw.")
- Reciprocating saw or "sabre saw" (UK and Australia): a saw
with an "in-and-out" or "up-and-down" action similar
to a jigsaw, but larger and more powerful, and using a longer stroke with
the blade parallel to the barrel. Hand-held versions, sometimes powered by
compressed air, are for demolition work or for cutting pipe. Before the
invention of the circular saw, sawmills used saws with this type of action; the two
most common versions were the sash saw or "frame saw"
and the muley or "mulay" saw.
- Scroll saw:
for making intricate curved cuts ("scrolls").
- Dragsaw:
for bucking logs (used before the invention of the chainsaw).
- Sternal saw: for cutting through a patient's sternum during
surgery.
Continuous
band
- Band saw:
a ripsaw on a motor-driven continuous band;
- Chainsaw:
a motor-driven
crosscut saw, principally for felling trees
and bucking logs.
Types
of blades and blade cuts
Most blade teeth are made either of
tool steel or carbide. Carbide is harder and holds a sharp edge much longer.
Band saw blade
A long band welded into a circle, with teeth on one side.
Compared to a circular-saw blade, it produces less waste because it is thinner,
dissipates heat better because it is longer (so there is more blade to do the
cutting, and is usually run at a slower speed.
Crosscut
In woodworking, a cut made at (or close to) a right angle to the direction
of the wood grain of the workpiece. A crosscut saw
is used to make this type of cut.
Rip cut
In woodworking, a cut made parallel to the direction of the
grain of the workpiece. A rip saw is used to make this type of cut.
Plytooth blade
A special type of circular saw blade used for making
wide-grooved cuts in wood so that the edge of another piece of wood will fit
into the groove to make a joint. Some dado blades can be adjusted to make
different-width grooves. A "stacked" dado blade, consisting of
chipper blades between two dado blades, can make different-width grooves by
adding or removing chipper blades. An "adjustable" dado blade has a
movable locking cam mechanism to adjust the degree to which the blade wobbles
sideways, allowing continuously variable groove widths from the lower to upper
design limits of the dado.
'Strobe saw blade]
A circular saw blade with special rakers/cutters to easily
saw through green or uncured wood that tends to jam other kinds of saw blades.
Materials
used for saws
There are several materials used in
saws, with each of its own specifications.
Mostly used in back saws
because of its low price and its flow characteristics, which make it relatively
easy to cast. Brass contributes to the rigidity that is needed in back saws,
which require less force to operate than other kinds of saws because of the
pulling motion involved.
Used in almost every existing kind of saw. Because steel is
cheap, easy to shape, and very strong, it has the right properties for most
kind of saws.
Fixed onto the saw blade's base to form diamond saw blades. As diamond is a superhard material, diamond saw blades can be used to cut hard brittle or
abrasive materials, for example, stone, concrete, asphalt, bricks, ceramics,
glass, semiconductor and gem stone. There are many methods used to fix the
diamonds onto the blades' base and there are various kinds of diamond saw
blades for different purposes.[9]
High speed steel (HSS)
The whole saw blade is made of High Speed Steel (HSS). HSS
saw blades are mainly used to cut steel, copper, aluminum and other metal
materials. If high-strength steels (e.g., stainless steel) are to be cut, the
blades made of cobalt HSS (e.g. M35, M42) should be used.[9]
- Carbide-tipped saw blades: The saw blade's teeth are tipped (via welding) with
small pieces of sharp tungsten carbide block. This type of blade is also
called TCT (Tungsten Carbide-Tipped) saw blade. Carbide-tipped saw blades
are widely used to cut wood, plywood, laminated board, plastic, grass,
aluminum and some other metals.
- Solid-carbide saw blades: The whole saw blade is made of tungsten carbide.
Comparing with HSS saw blades, solid-carbide saw blades have higher
hardness under high temperatures, and are more durable, but they also have
a lower toughness.
Uses
- Saws are commonly used for cutting hard materials. They
are used extensively in forestry, construction, demolition, medicine, and
hunting.
- Musical saws are used as instruments to make music.
- Chainsaw carving is a flourishing modern art form. Special saws have
been developed for the purpose.
- The production of lumber,
lengths of squared wood for use in construction, begins with the felling
of trees and the transportation of the logs to a sawmill.
Plainsawing: Lumber
that will be used in structures is typically plainsawn (also called flatsawn),
a method of dividing the log that produces the maximum yield of useful pieces
and therefore the greatest economy.
Quarter sawing: This sawing method produces edge-grain or vertical gain lumber,
in which annual growth rings run more consistently perpendicular to the pieces'
wider faces.
The entire wiki link can be found at: https://en.wikipedia.org/wiki/Saw
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