Part 6 (1/2)

[Ill.u.s.tration: Fig. 78. Grinding Angle, 20. Whetting Angle, 25.]

To test the sharpness of a whetted edge, draw the tip of the finger or thumb lightly along it, Fig. 79. If the edge be dull, it will feel smooth: if it be sharp, and if care be taken, it will score the skin a little, not enough to cut thru, but just enough to be felt.

[Ill.u.s.tration: Fig. 79. Testing the Sharpness of a Chisel.]

The _gouge_ is a form of chisel, the blade of which is concave, and hence the edge curved. When the bevel is on the outside, the common form, it is called an outside bevel gouge or simply a ”gouge,” Fig.

80; if the bevel is on the inside, it is called an inside bevel, or inside ground, or scribing-gouge, or paring-gouge, Fig. 81.[3]

[Footnote 3: Another confusing nomenclature (Goss) gives the name ”inside gouges” to those with the cutting edge on the inside, and ”outside gouges” to those with the cutting edge on the outside.]

Carving tools are, properly speaking, all chisels, and are of different shapes for facility in carving.

For ordinary gouging, Fig. 82, the blade is gripped firmly by the left hand with the knuckles up, so that a strong control can be exerted over it. The gouge is manipulated in much the same way as the chisel, and like the chisel it is used longitudinally, laterally, and transversely.

In working with the grain, by twisting the blade on its axis as it moves forward, delicate paring cuts may be made. This is particularly necessary in working cross-grained wood, and is a good ill.u.s.tration of the advantage of the sliding cut.

[Ill.u.s.tration: Fig. 80. Firmer-Gouge Outside Bevel.]

[Ill.u.s.tration: Fig. 81. Inside Bevel Gouge.]

In gouging out broad surfaces like trays or saddle seats it will be found of great advantage to work laterally, that is across the surface, especially in even grained woods as sweet gum. The tool is not so likely to slip off and run in as when working with the grain.

The gouge that is commonly used for cutting concave outlines on end grain, is the inside bevel gouge. Like the chisel in cutting convex outlines, it is pushed or driven perpendicularly thru the wood laid flat on a cutting board on the bench, as in perpendicular chiseling.

Fig. 72, p. 56.

[Ill.u.s.tration: Fig. 82. Gouging.]

In sharpening an outside bevel gouge, the main bevel is obtained on the grindstone, care being taken to keep the gouge rocking on its axis, so as to get an even curve. It is then whetted on the flat side of a slipstone, Fig. 83, the bevel already obtained on the grindstone being made slightly more obtuse at the edge. A good method is to rock the gouge on its axis with the left hand, while the slipstone held in the right hand is rubbed back and forth on the edge. Then the concave side is rubbed on the round edge of the slipstone, care being taken to avoid putting a bevel on it. Inside bevel gouges need to be ground on a carborundum or other revolving stone having a round edge. The outfit of the agacite grinder, (Fig. 224, p. 120), contains one of these stones. The whetting, of course, is the reverse of that on the outside bevel gouge.

[Ill.u.s.tration: Fig. 83. Whetting a Gouge.]

The _knife_ differs from the chisel in two respects, (1) the edge is along the side instead of the end, and (2) it has a two-beveled edge.

Knives are sometimes made with one side flat for certain kinds of paring work, but these are uncommon. The two-beveled edge is an advantage to the worker in enabling him to cut into the wood at any angle, but it is a disadvantage in that it is incapable of making flat surfaces. The knife is particularly valuable in woodwork for scoring and for certain emergencies. The sloyd knife, Fig. 84, is a tool likely to be misused in the hands of small children, but when sharp and in strong hands, has many valuable uses. A convenient size has a 2-1/2 inch blade. When grinding and whetting a knife, the fact that both sides are beveled alike should be kept in mind.

[Ill.u.s.tration: Fig. 84. Sloyd Knife.]

[Ill.u.s.tration: Fig. 85. Draw-Knife.]

The _draw-knife_, Fig. 85, is ground like a chisel, with the bevel only on one side, but the edge is along the side like a knife. Instead of being pushed into the wood, like a chisel, it is drawn into it by the handles which project in advance of the cutting edge. The handles are sometimes made to fold over the edge, and thus protect it when not in use. The size is indicated by the length of the cutting edge. It is particularly useful in reducing narrow surfaces and in slicing off large pieces, but it is liable to split rather than cut the wood.

SAWS.

[Ill.u.s.tration: Fig. 86. Hand Saw.]

The object of the saw is to cut thru a piece of material along a determined line. Its efficiency depends upon (1) the narrowness of the saw cut or ”kerf,” and (2) upon the force required to drive it thru the material. The thinner the blade, the less material will be cut out and wasted, and the less force will have to be applied. In order to have the saw as thin as possible, almost all the people of the world, except the Anglo Saxons, have saws that cut when they are pulled toward the worker. The blade is in tension while cutting and in compression only when being returned for a new cut. German carpenters use a saw like our turning-saw. English and Americans have developed the saw on the opposite principle, namely, that it should cut on the pus.h.i.+ng stroke. As a matter of fact, the crosscut-saw cuts somewhat on the back stroke. The pus.h.i.+ng stroke necessitates a thickening of the blade sufficient to prevent buckling,--a not uncommon occurrence in the bands of a novice, in spite of this thickening. But tho this requires more force, and involves more waste, there are the compensations that the arm can exert more pressure in pus.h.i.+ng than in pulling, especially when the worker stands upright or stoops over his work, and the stiffer wide blade acts as a guide to the sawyer. Each method has its advantages. Whatever may be true of hand-saws, in machine-saws the tension method, as ill.u.s.trated by the gang-saw and the band-saw, is steadily displacing the compression method utilized in the circular-saw. Many kinds of work, however, can be done only on the circular-saw.

In order to diminish the disadvantages of the thrusting stroke, the modern hand-saw, Fig. 86, has been gradually improved as the result of much experience and thought. The outline of the blade is tapered in width from handle to point; it is thicker also at the heel (the handle end) than at the point; its thickness also tapers from the teeth to the back. All these tapers gives stiffness where it is most needed.

It is made wide for the sake of giving steadiness in sawing. The fact that it is thinner at the back than along the teeth gives it clearance in pa.s.sing back and forth in the kerf, but the friction is still great, especially in sawing soft or damp wood. To avoid this binding still further, the teeth are ”set” alternately one to one side and the next to the other, and so on.

[Ill.u.s.tration: Fig. 87. Rip Saw Teeth: A-edge view, B-side view, C cross-section. Crosscut-Saw Teeth: A'-edge view, B'-side view, C'-cross-section.]