Set of a saw
With very few exceptions, every saw must have the teeth set. Set is a term applied to the alternate bending of the tip of each tooth from a straight line along the edge of the blade. The purpose of set is to make the saw-cut slightly wider than the thickness of the blade.
The crosscut saw is used to cut across the grain of the wood; the ripsaw is used to cut with the grain. The shape of the teeth determines the type of saw as well as its use in relation to the grain of the wood.
The crosscut saw
The teeth of a crosscut saw have a shape different from those of a ripsaw, and they work differently. The angle of rake on a crosscut saw is 75 degrees. The sides of each tooth are beveled or slanted to produce a sharp point at the top of each tooth.
While the ripsaw also does its work by removing some of the material to form the kerf, the shape of the teeth differs from that of the crosscut saw; for the ripsaw is used to cut with the grain, or parallel to the cells and fibers of the wood. Each tooth of a ripsaw has the rake angle filed at 90 degrees.
The ripsaw tooth, being straight in front, strikes the wood at right angles to the fibers; it cuts the fibers at this point and chips out a section of the material, as shown in Each successive tooth cuts its portion of the wood, and the chip so loosened is carried out of the kerf in the gullet of the tooth, which is the space between two teeth.
The hacksaw is another form of crosscut saw used for fine cutting. These saws range in sizes from 8" to 16" long. They can be obtained with teeth varying in size. They range from 12 to 16 points per inch. The blade of the backsaw is relatively thin, requiring the use of a reinforcement to keep it rigid. The reinforcement consists of a strip of heavy steel clamped over the back of the blade; it is from this reinforcing strip that the hacksaw gets its name.
When cutting small pieces of wood to length, t bench hook is generally used. The bench hook is a board about 6" X 10" with cleats fastened to opposite faces near the ends. One cleat, on the under face, hooks over the edge of the bench; the other cleat, on the upper face at the opposite end, is used to brace the stock against.
The stock to be cut is placed on the bench hook and held firmly against the cleat at the back. The cleat on the underside of the bench hook is in contact with the edge of the bench. The stock should be placed on the bench hook in such a manner that as the saw cuts through it will come in contact with the surface of the bench hook.
The compass saw
A compass saw is used to cut curves and circles in wood. It has a long blade, tapering to a point. Compass saws range in length from 10" to 18”, and have 8 teeth to the inch. The blade of the saw is relatively thick; therefore, a kerf cut with a compass saw is quite wide.
The keyhole saw
The keyhole saw has the same general appearance as the compass saw. Keyhole saws come in lengths ranging from 7" to 14", and have 10 points to the inch. They are used for fine work such as cutting small curves and cutting the slots of keyholes. When using the keyhole saw, the same instructions applying to the compass saw should be followed.
The coping saw
The coping saw is also used for cutting curves. It has a metal frame, a handle, and a removable blade. The blade is placed in the frame and held there by pins or loops which are part of the blade, or held in clamps which are part of the frame.
The better coping saws have frames equipped with blade-holding devices which can be revolved, making it possible to face the blade in any direction. The swivel at the upper end of the frame is free to move in any direction; the lower one, which has a threaded rod that screws into the handle, must be kept tight at all times.
The frame of a coping saw is longer than the blade that is fitted to it. This is necessary to keep tension on the saw blade. When placing a blade in the frame the handle is turned, thereby unscrewing the threaded rod of the lower swivel. The blade is fitted in the slots; and as the handle is turned, drawing in the threaded rod, the arms of the frame are drawn closer. The tension created thereby keeps the blade rigid. When inserting a blade in the frame, the teeth should point toward the handle so that the cutting is done on the pulling stroke rather than on the pushing stroke.
Although the swivel-blade holders are designed to permit the blade to be turned in any direction in relation to the frame, the pins on these swivels should always be in the same direction. Failure to keep these in line will twist the blade, so the saw will not follow a line. So will a loose lower swivel.
The hacksaw is used by the metalworker. Its essential parts are the frame, the handle, and the blade. The frame should be rigid enough to hold the blade firmly in line without being too heavy. Figure shows a hacksaw favored by many toolmakers and machinists. It is called the solid-frame type, which means that each saw is made for use with a blade of given length. This length may be 8", 9", 10", or 12". Blade tension is adjusted by turning the handle.
Some saws are made with adjustable frames. These frames, by simple adjustment, permit the use of several blade lengths.
Blades may be all-hard or flexible-back. In the flexible-back blades, only the teeth are hard. In benchwork, using a light, rigid saw frame, the all-hard blades give excellent service. When working in awkward positions and when the work cannot be held rigidly, the flexible blade gives more satisfactory service. The number of teeth per inch is very important in the selection of a blade for a given job. Standard blades are made with 14, 18, 24, and 32 teeth per inch. The conditions governing the selection of both frames will be discussed under the use of the hacksaw.
Conditioning a saw
In order to do its work, a saw must be kept in condition. The rake angle must be correct, the teeth must be set, and each tooth must be of like size and have its cutting edge at the proper angle. When it is necessary to recondition or sharpen a wood saw, each of these points must be checked carefully.
Jointing a saw
Shaping the teeth of a saw
After completing the jointing operation, shape the teeth. The teeth must be uniform in size, and must have the correct angle of rake. Crosscut-saw teeth have a rake angle of 75 degrees, and ripsaw teeth have a rake angle of 90 degrees. When shaping the teeth, disregard the bevel as shown on the crosscut, and shape the teeth with the file held at right angles to the saw blade. The saw blade is placed in a saw vise, with the first section to be worked on coming within the jaws of the vise. The teeth should be from 1/2" to 3/4" above the vise.
Setting a saw
When the teeth of a saw are correctly shaped, the next operation is setting. Setting a saw means the alternate bending or springing of the upper part of each tooth, one to the right and the next to the left, in order to make a saw kerf slightly wider than the thickness of the blade.
The amount of set given to any saw depends on the kind of wood and the condition of the wood. Wet soft woods require the use of a saw with more set than dry hard woods require. For fine work on any dry wood, whether it be hard wood or soft wood, a fine-tooth saw with a minimum of set should be used.
Sharpening a saw
When the saw has been properly set, the final operation is sharpening the teeth. This operation involves beveling the teeth on the crosscut saw or making a sharp chisel edge on those of the ripsaw.
To file a crosscut saw, place it in the saw vise with the handle to the right. The bottom of the gullets should be no more than 1/8" above the jaws of the vise.
If more of the blade projects, the saw will chatter. Starting at the end of the blade, pick out the first tooth that is set toward you. Place the file in the gullet to the left of this tooth, and swing the file toward the left so that it crosses the blade at an angle of 45 degrees.
Hold the file level, with one hand on the handle and the other on the end of the file. Do not allow the file to rock during the filing operation. The pressure should be applied on the push stroke, and the file should be lifted slightly on the return stroke. Dragging the file back over the teeth on the return stroke will dull the file. This operation files the teeth to the left and right of the file at the same time.
Continue the filing operation in the same gullet until the sides of the teeth in contact with the file are brought to a point. Remove the file from the first gullet, and skip the next gullet, placing the file in the third gullet. Filing is continued until the adjacent sides are brought to a point. Continue in this manner, skipping every other gullet, until the handle end of the saw is reached.
Now remove the saw from the vise and replace it so that the blade is to the right. Place the file in the gullet to the right of the first tooth that is set toward you, with the file swung around at an angle of 45 degrees across the blade.
Work the file back and forth in the gullet between these teeth, maintaining the correct angle during the operation. Continue filing until the sides of these teeth are beveled to the point of the tooth. Continue placing the file in every second gullet, which is the gullet to the right of the tooth set toward you, until the saw handle is reached.
The filing of a ripsaw is identical to that of the crosscut saw, with one exception: When filing a ripsaw the file, instead of being swung around at an angle of 45 degrees, is placed in the gullet at right angles to the blade.