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A hacksaw is a fine-tooth hand saw with a blade held under tension in a frame, used for cutting materials such as metal or plastics. Hand-held hacksaws consist of a metal arch with a handle, usually a pistol grip, with pins for attaching a narrow disposable blade. A screw or other mechanism is used to put the thin blade under tension. 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. On the push stroke, the arch will flex slightly, decreasing the tension on the blade, often resulting in an increased tendency of the blade to buckle and crack. Cutting on the pull stroke increases the blade tension and will result in greater control of the cut and longer blade life.
Blades are available in standardized lengths, usually 10 or 12 inches for a standard hand hacksaw. "Junior" hacksaws are half this size. 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 (tpi) 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 (not tightly controlled)
Mounting Hole diameter: 9/64 to 5/32 inch / 3.5 to 4 mm (not tightly controlled)
Blade Width: 7/16 to 33/64 inch / 11 to 13 mm (not tightly controlled)
Blade Thickness: 0.020 to 0.027 inches / 0.5 to 0.70 mm (varies with tooth pitch and other factors)
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 (not tightly controlled)
A panel hacksaw eliminates the frame, so that the saw can 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 (or electric 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. 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.
While stationary electric hacksaws are reasonably uncommon they are still produced but saws powered by a stationary engines have gone out of fashion. The reason for using one is that they provide a cleaner cut than an angle grinder or other types of saw. Large, power hacksaws are sometimes used in place of a bandsaw for cutting metal stock to length.
See also 
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- Machinery's Handbook, 14th Edition, by Erik Oberg & F. D. Jones, The Industrial Press, 1952, pages 1390-1391
- "Power Hacksaw 200mm Capacity c/w Coolant System". Jnkcomponents.co.uk. Retrieved 2009-12-02.