A hacksaw is a fine-toothed saw, originally and principally for cutting metal. They can
also cut various other materials, such as plastic and wood; for example, plumbers and
electricians often cut plastic pipe and plastic conduit with them. There are hand saw versions
and powered versions. Most hacksaws are hand saws with a C-shaped frame that holds a blade
under tension. Such hacksaws have a handle, usually a pistol grip, with pins for attaching
a narrow disposable blade. The frames may also be adjustable to accommodate blades of
different sizes. A screw or other mechanism is used to put the thin blade under tension.
Panel hacksaws, forgo the frame and instead have a sheet metal body; they can cut into
a sheet metal panel further than a frame would allow. These saws are no longer commonly available
but hacksaw blade holders enable standard hacksaw blades to be used similarly to a Keyhole
saw or Pad saw. Power tools including Nibblers, Jigsaws and Angle Grinders fitted with metal
cutting blades and discs are now used for longer cuts in sheet metals.
On hacksaws, as with most frame saws, the blade can be mounted with the teeth facing
toward or away from the handle, resulting in cutting action on either the push or pull
stroke. In normal use, cutting vertically downwards with work held in a bench vice,
hacksaw blades should be set to be facing forwards. Some frame saws, including Fret
Saws and Piercing Saws, have their blades set to be facing the handle because they are
used to cut by being pulled down against a horizontal surface.
Design History
While saws for cutting metal had been in used for many years, significant improvements in
longevity and efficiency were made in the 1880s by George N. Clemson, a founder of Clemson
Bros., Inc of Middletown, New York, USA,. Clemson conducted tests which involved changing
the dimensions, shapes of teeth, styles of set, and variable heat treatments of blades.
Clemson claimed enormous improvements to the cutting ability of blades and built a major
industrial operation manufacturing hacksaw blades sold under the trade name Star Hack
Saw. In 1898, Clemson was granted US Patent 601947, which details various improvements
in the hacksaw. Blades
Blades are available in standardized lengths, usually 10 or 12 inches for a standard hand
hacksaw. "Junior" hacksaws are typically 150mm long. Powered hacksaws may use large blades
in a range of sizes, or small machines may use the same hand blades.
The pitch of the teeth can be anywhere from fourteen to thirty-two teeth per inch for
a hand blade, with as few as three tpi for a large power hacksaw blade. The blade chosen
is based on the thickness of the material being cut, with a minimum of three teeth in
the material. As hacksaw teeth are so small, they are set in a "wave" set. As for other
saws they are set from side to side to provide a kerf or clearance when sawing, but the set
of a hacksaw changes gradually from tooth to tooth in a smooth curve, rather than alternate
teeth set left and right. Hacksaw blades are normally quite brittle,
so care needs to be taken to prevent brittle fracture of the blade. Early blades were of
carbon steel, now termed 'low alloy' blades, and were relatively soft and flexible. They
avoided breakage, but also wore out rapidly. Except where cost is a particular concern,
this type is now obsolete. 'Low alloy' blades are still the only type available for the
Junior hacksaw, which limits the usefulness of this otherwise popular saw.
For several decades now, hacksaw blades have used high speed steel for their teeth, giving
greatly improved cutting and tooth life. These blades were first available in the 'All-hard'
form which cut accurately but were extremely brittle. This limited their practical use
to benchwork on a workpiece that was firmly clamped in a vice. A softer form of high speed
steel blade was also available, which wore well and resisted breakage, but was less stiff
and so less accurate for precise sawing. Since the 1980s, bi-metal blades have been used
to give the advantages of both forms, without risk of breakage. A strip of high speed steel
along the tooth edge is electron beam welded to a softer spine. As the price of these has
dropped to be comparable with the older blades, their use is now almost universal.
Hacksaw blade specifications: The most common blade is the 12 inch or 300 mm length. Hacksaw
blades have two holes near the ends for mounting them in the saw frame and the 12 inch / 300 mm
dimension refers to the center to center distance between these mounting holes.
12 Inch Blade: Hole to Hole: 11 7/8 inches / 300 mm
Overall blade length: 12 3/8 inches / 315 mm Mounting Hole diameter: 9/64 to 5/32 inch
/ 3.5 to 4 mm Blade Width: 7/16 to 33/64 inch / 11 to 13 mm
Blade Thickness: 0.020 to 0.027 inches / 0.5 to 0.70 mm
The kerf produced by the blades is somewhat wider than the blade thickness due to the
set of the teeth. It commonly varies between 0.030 and 0.063 inches / 0.75 and 1.6 mm
depending on the pitch and set of the teeth. The 10 inch blade is also fairly common and
all the above dimensions apply except for the following:
Hole to Hole: 9 7/8 inches / 250 mm Overall blade length: 10 3/8 inches / 265 mm
Variants
A panel hacksaw eliminated the frame, so that the saw could cut into panels of sheet metal
without the length of cut being restricted by the frame.
Junior hacksaws are the small variant, while larger mechanical hacksaws are used to cut
working pieces from bulk metal. A power hacksaw is a type of hacksaw that
is powered either by its own electric motor or connected to a stationary engine. Most
power hacksaws are stationary machines but some portable models do exist; the latter
have been displaced to some extent by reciprocating saws such as the Sawzall, which accept blades
with hacksaw teeth. Stationary models usually have a mechanism to lift up the saw blade
on the return stroke and some have a coolant pump to prevent the saw blade from overheating.
Power hacksaws are not as commonly used in the metalworking industries as they once were.
Bandsaws and cold saws have mostly displaced them. While stationary electric hacksaws are
not very common, they are still produced. Power hacksaws of the type powered by stationary
engines and line shafts, like other line-shaft-powered machines, are now rare; museums and antique-tool
hobbyists still preserve a few of them. See also
Coping saw Fretsaw
Piercing saw References