5. Saws. The saw might be described as a succession of chisels, one back of the other. We can readily understand the action of the saw by making cuts with a narrow chisel along the grain of a piece of wood, as shown in Fig. 10 at a.
Fig. 10. Cutting with and across the Grain with a Narrow Chisel
The little pieces of wood removed in this way are similar to the sawdust made by the saw, the only difference being that in the saw the teeth are narrower and the little pieces consequently smaller, and instead of one chisel dozens are being pushed forward at one time.
A saw with these chisel-shaped teeth, and used for cutting along the grain, is called a ripsaw.
That this tool will not cut so readily across the grain may easily be proved by again resorting to the narrow chisel and attempting to repeat the first experiment. The wood will act as shown in Fig. 10 at b, splitting along the grain in both directions. It is quite evident, then, that a tool for cutting across the grain must be constructed in some other way.
Fig. 11. The Saw
Continuing this experiment, let us cut the fibers with a knife point in two parallel lines across the grain, close together, as at c. It will be found that the wood between these lines may now be easily removed with the narrow chisel. This fact is made the basis on which we construct the crosscut saw. Every tooth is sharpened to a point, one on the right side, the next on the left, giving two parallel lines of sharp points designed to cut the fibers, as was done in our experiment with the knife. Fig. 12 shows the end view of the crosscut teeth enlarged. Observe that not only are the alternate teeth sharpened on opposite sides, but each tooth is bent outward from the body of the saw. This bending is called set, and is designed to make the saw cut, or kerf, wider than the thickness of the saw, that the latter may pass easily through the wood after the teeth have done their work. If it were not for this set, the fibers would spring back against the body of the saw after the teeth had passed and make the work very laborious. When a saw is properly set it should pass through the wood easily.
Fig. 12. Teeth of Crosscut Saw
Fig. 13. Teeth of Ripsaw
The teeth of the ripsaw are also set, but, as will be seen in the sketch, the bottoms are flat like a chisel instead of pointed like those of the crosscut teeth.
Beside the end views of the two kinds of teeth, the side views, which are also different, are shown in Figs. 12 and 13.
We are inclined to think of the saw as a very commonplace article, yet a careful examination will prove that the greatest care and skill are needed in its manufacture. Observe that the body, which must be of the best steel, tapers, being considerably wider at the handle than at the opposite end. This is to give strength, and to prevent buckling, or bending, as the tool is pushed forward.
Fig. 14. Body of Saw, showing Tapers
Most delicate measurements must be made, however, to discover that not only the width but the thickness increases from A to B, and decreases from C to D. How carefully this tapering must be done can be realized when we know that the difference in thickness from A to B is only three one-thousandths of an inch, and from C to D twelve one-thousandths at end A and five one-thousandths at end B.
Fig. 15. Method of holding the Saw
The saw should be held in the right hand, with the left grasping the board. The thumb of the left hand acts as guide, the saw is tilted, as shown in Fig. 15, and drawn toward the worker at the first stroke. This tool should be used without exerting much pressure, in accordance with the general rule that we do our best work with tools when we work easily and deliberately.
Fig. 16. The Backsaw
Many varieties of saws are designed for special purposes, including those which cut stone and metal.
Fig. 17. Method of using the Backsaw and Bench Hook
6. Backsaw. The backsaw is a crosscut saw with small teeth, and has a heavy steel backpiece, Fig. 17, to prevent bending. In this respect it differs from the ordinary crosscut varieties, which bend readily. The purpose of the backsaw is to make fine, straight cuts in delicate, accurate work. The steel back B is necessary on account of the thin blade, but on account of the thickness of B no cut can be made deeper than the line C. This tool will cut in any direction with reference to the grain, but is primarily a crosscut saw.
Fig. 18. The Bench Hook
Fig. 19. The Turning Saw
7. The Turning Saw. In ordinary work the saw is supposed to cut to a straight line, but there are certain classes of work where it is desirable to follow a curved line, and consequently a special tool is necessary. The turning saw shown in the cut is used for this purpose. The handles holding the saw blade may be turned in any direction with reference to the frame.
8. The Plane. The plane reduces our rough lumber to planed, or dressed, stock. The cutting part is a thin, wide chisel called the plane iron.
Fig. 20. The Plane Iron in Action
Fig. 20 shows the position of the plane iron in operation. Assume the iron to be moving in the direction of the arrow on a piece of wood. The sharp point would enter the board and, should the grain be unfavorable, start a splitting action, as shown at a.
We wish to smooth the wood instead of roughing it, and must in some way stop the splitting. This is accomplished by placing a cap iron on the plane iron, as shown at b. The cap bends and breaks the shaving before the splitting action has a chance to begin, and gives the spiral form so familiar in wood shavings.
Fig. 21. Plane Iron, Cap, and Set Screw
The cap is firmly fastened to the plane iron by a stout screw, and this whole combination is fastened in the throat of the plane by a clamp (Fig. 22). The opening on the bottom of the plane through which the cutting edge protrudes is called the mouth of the plane.
Fig. 22. Sectional Views of Iron Plane
9. Adjustment of Plane. There are two ways of adjusting a modern iron plane,—by means of the set screw s, and of the lever l.
Screw s lowers or raises the plane iron so that we may take a thin or thick shaving, and lever l straightens the iron, which is liable to project more on one side than on the other, and will then take a shaving thicker on one side than on the other.
Before using the plane always examine it carefully. Invert the tool, holding it toward the light with the toe toward you, and glance along the bottom. If the iron projects, observe whether it is even, and if not, move the lever until it is. For a thin shaving the cutting edge should appear as a black line of uniform thickness. For a heavy shaving turn the brass screw until the iron projects slightly.
In using the plane avoid a stooping position. Stand with the right side to the bench and with the shoulders thrown back. Let the pressure of the left hand be greater at the beginning and that of the right hand at the end of the stroke. The tool should rest perfectly flat on the wood from start to finish.
Fig. 23. Irons of Smooth and Jack Planes
10. The Jack Plane. The ordinary plane iron has a straight edge, as shown at a, Fig. 23, but when a large quantity of wood is to be removed the iron is sharpened in the shape shown at b. This curved iron will cut out the wood in hollows, leaving ridges between, and it is necessary to follow this jack plane with a finer one having a straight edge in order to smooth the surface. The jack plane might be called a roughing plane.
Fig. 24. Relative Sizes of Smooth and Jack Planes
The lower figure is a jack plane
11. The Smooth Plane. The smoothing plane is shorter than the jack plane, its object being to smooth the surface without regard to straightening it, as it is supposed that the straightening has previously been done. The cap iron in the smooth plane should be set from a sixteenth to a thirty-second of an inch from the cutting edge of the plane iron.
Fig. 25. Action of Short and Long Planes
12. Jointers. For straightening very rough and uneven stock a long plane is necessary (Fig. 25). In the illustration let line ab represent the edge of a very uneven board. A short plane c would simply follow the hills and hollows, smoothing but not straightening it, while a long plane, as shown at d, would merely cut off the top of the high places, as shown by the dotted line, and would not touch the bottoms of the hollows until all the elevations were leveled; in other words, until the surface was straightened. Such planes, which are often three feet long or more, are called jointers.
Fig. 26. The Block Plane
13. The Block Plane. To square the end of a piece of stock the conditions are quite different from those just described where we were planing with the grain. In end planing no cap iron is necessary, the plane iron in the block plane being reversed with bevel side up.
This tool requires more care than the others, as the stroke is usually quite short, and if the cutting edge is allowed to reach the farther corner, the latter will be broken off.
Fig. 27. Method of using Block Plane
To avoid this error the plane must be lifted up before the end of the stroke, as shown by the dotted line a. The piece is then reversed, and planed as shown by arrow b. In this way the whole end is smoothed, without ruining the corners.
Besides these standard planes there are many patent and special ones for cutting tongues, grooves, beads, etc.
14. The Wooden Plane. Although the iron-bodied planes just described are now in common use, the old-fashioned wooden plane is still the favorite of many woodworkers.
Fig. 28. The Wooden Plane
This tool, while lacking some of the adjustments of the iron plane, was much simpler and contained a smaller number of parts.
The iron and cap were held in position by a wooden wedge, which was driven in by a light blow of the hammer. The workman removed the iron and wedge by turning the plane upside down and striking the forward part a light downward blow on the bench, while the thickness of the shaving was increased by a light tap on the plane iron.
One of the chief objections to the wooden plane was its liability to wear and warp, so that it became necessary to straighten, or joint, the face. No such difficulty is encountered in the iron-bodied plane.
15. The Chisel. The chisel is one of the simplest forms of cutting tools. The size of the angle a depends on the kind of material to be cut.
Fig. 29. Cutting Angle of Chisel
A chisel for cutting wood must be sharpened to an angle of from 30 to 35 degrees.
By careless sharpening an extra bevel is sometimes formed, as shown at b.
The cutting angle is then no sharper than if the chisel were shaped like that shown by dotted lines, and care must always be taken when sharpening to keep the line cd straight, so that angle a will be the real cutting angle.
Two classes of chisels are in common use: the framing chisel used for heavy work, such as the frames of buildings; and the firmer chisel. The framing chisel is strong and heavy, and has a handle capable of withstanding the blows of a mallet. The firmer chisel is designed for finer and lighter work without the mallet.
Fig. 30. The Framing Chisel
Fig. 31. The Firmer Chisel
Fig. 32. Proper Position for Horizontal Chiseling
The chisel must be sharp if we wish to do good and accurate work, and a cut on the hand made by such a sharp tool is liable to be a deep one. Special care must be used in handling it, keeping both hands away from the cutting edge, as shown in the sketch, and placing it when not in use where it cannot be pushed off the bench on to the floor or the student’s feet.
Fig. 32 shows the method of using the tool on horizontal work, and Fig. 33 for vertical cutting. For this kind of work only a small portion of the cutting edge can be used, the student judging for himself how heavy a cut to take by the hardness of the wood and amount of strength required. Good work can never be done when one has to exert all his strength on the tool. The best results are obtained when we work easily.
Fig. 33. Proper Position for Vertical Chiseling
Better work can usually be done with the chisel if, instead of pushing it straight ahead or straight downward, we incline it somewhat so as to secure a slight paring action.
Fig. 34. Sharpening Chisel on Oilstone
When the chisel becomes dull, unless its edge has been nicked or ruined by some accident, it is only necessary to sharpen it on the oilstone. Hold the tool with the bevel flat on the stone. A drop or two of oil may be used to lubricate the stone, the tool being worked back and forth on the face of it. Especial care must be taken to avoid a rocking motion, which will produce a curved edge instead of a flat one.
Fig. 35. Common Forms of the Brace
After the rubbing, reverse the chisel, lay the flat side firmly on the stone, and draw toward you. This is to straighten the wire edge which has been turned over by the rubbing. The wire edge may then be removed by drawing the cutting edge across the end of a block of wood. When the chisel is nicked or very dull it must be ground on the grindstone.
16. Brace and Bit. The old-fashioned augers and gimlets have given way to the modern brace and bit.
Fig. 36. The Center Bit
The brace, which is sometimes called the bitstock, allows both hands to be used continuously, which was not true of the old-fashioned auger. Several varieties of the brace are in use, the ones shown in the cuts being common.
Bits are designed for a variety of purposes, the name being applied to a tool which is to be turned by the brace. The old-fashioned center bit shown in the cut possessed most of the essentials of a good boring tool.
Fig. 37. The Auger Bit
The sharp spur in the center allowed the hole to be accurately placed. The lip on the outer edge cut the fibers in a circle before the chisel edge began to remove the wood, and so a smooth hole could be bored; but considerable pressure was necessary to force the tool through the wood.
The progress that has been made in the manufacture of tools can be easily appreciated by comparing this center bit with the modern auger bit.
Referring to the sketch (Fig. 38), B B are two knife points, or nibs, which cut the wood fibers before the chisel edges, or lips, C C, can touch the wood. The point A allows us to accurately place the center of the hole where we wish it, and the screw back of A draws the tool into the wood as it revolves. This part is known as the spur, or worm. On this class of bits no pressure is necessary.
Fig. 38. Details of Auger Bit
The opposite end of the bit, called the shank, fits into the brace. Any tool with such a shank, and designed for use with the brace, is a bit. We have screw-driver bits, gimlet bits, auger bits, etc.
On the shank of an auger bit will be found a number. This is the numerator of a fraction whose denominator is 16. If we find this number to be 4, it is a ⁴⁄₁₆, or a ¼-inch bit. If the number is 16, we have a ¹⁶⁄₁₆, or a one-inch bit, etc., always referring to the diameter of the hole which the tool will bore.
In using the brace and bit care must be taken to see that the bit shank is far enough in the brace to be fastened securely, and that the tool is held at right angles to the wood. It may appear from the front to be perfectly vertical, yet by stepping to one side and looking at it from another position it will frequently be found far from vertical. When starting a hole it is well to do this several times until assured that the tool is working in a true upright position.
Fig. 39. The Gimlet Bit
Fig. 40. The Countersink Bit
The gimlet bit is used for small holes, such as we make for screws. In this case the hole must be countersunk to receive the screw head, when flat-headed screws are used. The countersink bit is shown in the cut, and its purpose is more fully explained in the chapter on screws.
17. The Spokeshave. The spokeshave is practically a short plane with handles at the side so that the tool may be drawn or pushed. It may be adjusted by means of screws to take light or heavy shavings, and is used principally to smooth curved surfaces. The forming of a hammer handle is a good illustration of the kind of work it will do. It may be worked toward or away from the worker, and is an exceedingly handy tool.
Fig. 41. The Iron Spokeshave