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.