Kitabı oku: «Handwork in Wood», sayfa 5

The plug-cutter, Fig. 131, is useful for cutting plugs with which to cover the heads of screws that are deeply countersunk.

Center-bits, Fig. 132, work on the same principle as auger-bits, except that the spurs have no screw, and hence have to be pushed forcibly into the wood. Sizes are given in 16ths of an inch. They are useful for soft wood, and in boring large holes in thin material which is likely to split. They are sharpened in the same way as auger-bits.

Foerstner bits, Fig. 133, are peculiar in having no spur, but are centered by a sharp edge around the circumference. The size is indicated on the tang, in 16ths of an inch. They are useful in boring into end grain, and in boring part way into wood so thin that a spur would pierce thru. They can be sharpened only with special appliances.

Expansive-bits, Fig. 134, are so made as to bore holes of different sizes by adjusting the movable nib and cutter. There are two sizes, the small one with two cutters, boring from ½" to 1½" and the large one with three cutters boring from ⅞" to 4". They are very useful on particular occasions, but have to be used with care.

Reamers, Fig. 135, are used for enlarging holes already made. They are made square, half-round and six cornered in shape.

Countersinks, Fig. 136, are reamers in the shape of a flat cone, and are used to make holes for the heads of screws. The rose countersink is the most satisfactory form.

Fig 138. Washer-Cutter.

The washer-cutter, Fig. 138, is useful not only for cutting out washers but also for cutting holes in thin wood. The size is adjustable.

3. CHOPPING TOOLS

The primitive celt, which was hardly more than a wedge, has been differentiated into three modern hand tools, the chisel, see above, p. 53, the ax, Fig. 139, and the adze, Fig. 141.

The ax has also been differentiated into the hatchet, with a short handle, for use with one hand, while the ax-handle is long, for use with two hands. Its shape is an adaption to its manner of use. It is oval in order to be strongest in the direction of the blow and also in order that the axman may feel and guide the direction of the blade. The curve at the end is to avoid the awkward raising of the left hand at the moment of striking the blow, and the knob keeps it from slipping thru the hand. In both ax and hatchet there is a two-beveled edge. This is for the sake of facility in cutting into the wood at any angle.

There are two principal forms, the common ax and the two bitted ax, the latter used chiefly in lumbering. There is also a wedge-shaped ax for splitting wood. As among all tools, there is among axes a great variety for special uses.

The hatchet has, beside the cutting edge, a head for driving nails, and a notch for drawing them, thus combining three tools in one. The shingling hatchet, Fig. 140, is a type of this.

The adze, the carpenter's house adze, Fig. 141, is flat on the lower side, since its use is for straightening surfaces.

WOOD HAND TOOLS

References:¹⁰

(1) Cutting.

Goss, p. 22.

Smith, R. H., pp. 1-8.

Chisel.

Barnard, pp. 59-73.

Selden, pp. 44-50, 145-147.

Barter, pp. 93-96.

Griffith, pp. 53-64.

Goss, pp. 20-26.

Sickels, pp. 64-67.

Wheeler, 357, 421, 442.

Knife.

Barnard, pp. 48-58.

Selden, pp. 26-28, 158.

Saw.

Griffith, pp. 20-27.

Barnard, pp. 114-124.

Selden, pp. 41-43, 179-182.

Wheeler, pp. 466-473.

Hammacher, pp. 309-366.

Goss, pp. 26-41.

Sickels, pp. 76-79, 84.

Smith, R. H., 43-55.

Diston, pp. 129-138.

Plane.

Barnard, pp. 74-80.

Selden, pp. 11-26, 165-175.

Sickels pp. 72-75, 116.

Wheeler, pp. 445-458.

Hammacher, pp. 377-400.

Smith, R. H., pp. 16-31.

Larsson, p. 19.

Goss, pp. 41-52.

Barter, pp. 96-109.

Griffith, pp. 28-45.

(2) Boring Tools.

Barnard, pp. 125-135.

Goss, pp. 53-59.

Griffith, pp. 47-52.

Seldon, pp. 38-40, 141-144.

Wheeler, pp. 353-356.

(3) Chopping Tools.

Barnard, pp. 80-88.

Chapter IV, Continued.
WOOD HAND TOOLS

4. SCRAPING TOOLS

Scraping tools are of such nature that they can only abrade or smooth surfaces.

Files. Figs. 142-146, are formed with a series of cutting edges or teeth. These teeth are cut when the metal is soft and cold and then the tool is hardened. There are in use at least three thousand varieties of files, each of which is adapted to its particular purpose. Lengths are measured from point to heel exclusive of the tang. They are classified: (1) according to their outlines into blunt, (i. e., having a uniform cross section thruout), and taper; (2) according to the shape of their cross-section, into flat, square, three-square or triangular, knife, round or rat-tail, half-round, etc.; (3) according to the manner of their serrations, into single cut or "float" (having single, unbroken, parallel, chisel cuts across the surface), double-cut, (having two sets of chisel cuts crossing each other obliquely,) open cut, (having series of parallel cuts, slightly staggered,) and safe edge, (or side,) having one or more uncut surfaces; and (4) according to the fineness of the cut, as rough, bastard, second cut, smooth, and dead smooth. The "mill file," a very common form, is a flat, tapered, single-cut file.

Rasps, Fig. 147, differ from files in that instead of having cutting teeth made by lines, coarse projections are made by making indentations with a triangular point when the iron is soft. The difference between files and rasps is clearly shown in Fig. 149.

Fig. 149. a. Diagram of a Rasp Tooth.

b. Cross-Section of a Single-Cut File.

It is a good rule that files and rasps are to be used on wood only as a last resort, when no cutting tool will serve. Great care must be taken to file flat, not letting the tool rock. It is better to file only on the forward stroke, for that is the way the teeth are made to cut, and a flatter surface is more likely to be obtained.

Both files and rasps can be cleaned with a file-card, Fig. 148. They are sometimes sharpened with a sandblast, but ordinarily when dull are discarded.

Scrapers are thin, flat pieces of steel. They may be rectangular, or some of the edges may be curved. For scraping hollow surfaces curved scrapers of various shapes are necessary. Convenient shapes are shown in Fig. 150. The cutting power of scrapers depends upon the delicate burr or feather along their edges. When properly sharpened they take off not dust but fine shavings. Scrapers are particularly useful in smoothing cross-grained pieces of wood, and in cleaning off glue, old varnish, etc.

Fig. 150. Molding-Scrapers.

There are various devices for holding scrapers in frames or handles, such as the scraper-plane, Fig. 111, p. 79, the veneer-scraper, and box-scrapers. The veneer-scraper, Fig. 151, has the advantage that the blade may be sprung to a slight curve by a thumb-screw in the middle of the back, just as an ordinary scraper is when held in the hands.

Fig. 151. Using a Veneer-Scraper.

In use, Fig. 152, the scraper may be either pushed or pulled. When pushed, the scraper is held firmly in both hands, the fingers on the forward and the thumbs on the back side. It is tilted forward, away from the operator, far enough so that it will not chatter and is bowed back slightly, by pressure of the thumbs, so that there is no risk of the corners digging in. When pulled the position is reversed.

Fig. 152. Using a Cabinet-Scraper.

One method of sharpening the scraper is as follows: the scraper is first brought to the desired shape, straight or curved. This may be done either by grinding on the grindstone or by filing with a smooth, flat file, the scraper, while held in a vise. The edge is then carefully draw-filed, i. e., the file, a smooth one, is held (one hand at each end) directly at right angles to the edge of the scraper, Fig. 153, and moved sidewise from end to end of the scraper, until the edge is quite square with the sides. Then the scraper is laid flat on the oilstone and rubbed, first on one side and then on the other till the sides are bright and smooth along the edge, Fig. 154. Then it is set on edge on the stone and rubbed till there are two sharp square corners all along the edge, Fig. 155. Then it is put in the vise again and by means of a burnisher, or scraper steel, both of these corners are carefully turned or bent over so as to form a fine burr. This is done by tipping the scraper steel at a slight angle with the edge and rubbing it firmly along the sharp corner, Fig. 156.

Fig. 153. Sharpening a Cabinet-Scraper: 1st Step, Drawfiling.

Fig. 154. Sharpening a Cabinet-Scraper: 2nd Step, Whetting.

Fig. 155. Sharpening a Cabinet-Scraper: 3rd Step, Removing the Wire-Edge.

Fig. 156. Sharpening a Cabinet-Scraper: 4th Step, Turning the Edge.

To resharpen the scraper it is not necessary to file it afresh every time, but only to flatten out the edges and turn them again with slightly more bevel. Instead of using the oilstone an easier, tho less perfect, way to flatten out the burr on the edges is to lay the scraper flat on the bench near the edge. The scraper steel is then passed rapidly to and fro on the flat side of the scraper, Fig. 157. After that the edge should be turned as before.

Fig. 157. Resharpening a Cabinet-Scraper: Flattening the Edge.

Sandpaper. The "sand" is crushed quartz and is very hard and sharp. Other materials on paper or cloth are also used, as carborundum, emery, and so on. Sandpaper comes in various grades of coarseness from No. 00 (the finest) to No. 3, indicated on the back of each sheet. For ordinary purposes No. 00 and No. 1 are sufficient. Sandpaper sheets may readily be torn by placing the sanded side down, one-half of the sheet projecting over the square edge of the bench. With a quick downward motion the projecting portion easily parts. Or it may be torn straight by laying the sandpaper on a bench, sand side down, holding the teeth of a back-saw along the line to be torn. In this case, the smooth surface of the sandpaper would be against the saw.

Sandpaper should never be used to scrape and scrub work into shape, but only to obtain an extra smoothness. Nor ordinarily should it be used on a piece of wood until all the work with cutting tools is done, for the fine particles of sand remaining in the wood dull the edge of the tool. Sometimes in a piece of cross-grained wood rough places will be discovered by sandpapering. The surface should then be wiped free of sand and scraped before using a cutting tool again. In order to avoid cross scratches, work should be "sanded" with the grain, even if this takes much trouble. For flat surfaces, and to touch off edges, it is best to wrap the sandpaper over a rectangular block of wood, of which the corners are slightly rounded, or it may be fitted over special shapes of wood for specially shaped surfaces. The objection to using the thumb or fingers instead of a block, is that the soft portions of the wood are cut down faster than the hard portions, whereas the use of a block tends to keep the surface even.

Steel wool is made by turning off fine shavings from the edges of a number of thin discs of steel, held together in a lathe. There are various grades of coarseness, from No. 00 to No. 3. Its uses are manifold: as a substitute for sandpaper, especially on curved surfaces, to clean up paint, and to rub down shellac to an "egg-shell" finish. Like sandpaper it should not be used till all the work with cutting tools is done. It can be manipulated until utterly worn out.

5. POUNDING TOOLS

The hammer consists of two distinct parts, the head and the handle. The head is made of steel, so hard that it will not be indented by hitting against nails or the butt of nailsets, punches, etc., which are comparatively soft. It can easily be injured tho, by being driven against steel harder than itself. The handle is of hickory and of an oval shape to prevent its twisting in the hand.

Hammers may be classified as follows: (1) hammers for striking blows only; as, the blacksmith's hammer and the stone-mason's hammer, and (2) compound hammers, which consist of two tools combined, the face for striking, and the "peen" which may be a claw, pick, wedge, shovel, chisel, awl or round head for other uses. There are altogether about fifty styles of hammers varying in size from a jeweler's hammer to a blacksmith's great straight-handled sledge-hammer, weighing twenty pounds or more. They are named mostly according to their uses; as, the riveting-hammer, Fig. 159, the upholsterer's hammer, Fig. 160, the veneering-hammer, Fig. 162, etc. Magnetized hammers, Fig. 161, are used in many trades for driving brads and tacks, where it is hard to hold them in place with the fingers.

In the "bell-faced" hammer, the face is slightly convex, in order that the last blow in driving nails may set the nail-head below the surface. It is more difficult to strike a square blow with it than with a plain-faced hammer. For ordinary woodwork the plain-faced, that is, flat-faced claw-hammer, Fig. 158, is best. It is commonly used in carpenter work.

It is essential that the face of the hammer be kept free from glue in order to avoid its sticking on the nail-head and so bending the nail. Hammers should be used to hit iron only; for hitting wood, mallets are used. In striking with the hammer, the wrist, the elbow and the shoulder are one or all brought into play, according to the hardness of the blow. The essential precautions are that the handle be grasped at the end, that the blow be square and quick, and that the wood be not injured. At the last blow the hammer should not follow the nail, but should be brought back with a quick rebound. To send the nail below the surface, a nailset is used. (See below.)

The claw is used for extracting nails. To protect the wood in withdrawing a nail a block may be put under the hammer-head. When a nail is partly drawn, the leverage can be greatly increased by continuing to block up in this way, Fig. 163.

Fig. 163. Drawing a Nail with Claw-Hammer.

Fig. 164. Mallets.

The mallet, Fig. 164, differs from the hammer in having a wooden instead of a steel head. A maul or beetle is a heavy wooden mallet. The effect of the blow of a mallet is quite different from that of a hammer, in that the force is exerted more gradually; whereas the effect of the hammer blow is direct, immediate, and local, and is taken up at once. But a mallet continues to act after the first impulse, pushing, as it were. This is because of the elasticity of the head. A chisel, therefore, should always be driven with a mallet, for the chisel handle would soon go to pieces under the blows of a hammer, because of their suddenness; whereas the mallet blow which is slower will not only drive the blade deeper with the same force, but will not injure the handle so rapidly. Mallet-heads are made square, cylindrical, and barrel-shaped. Carver's mallets are often turned from one piece, hammer and head on one axis.

Nailsets, Fig. 165, are made with hardened points, but softer butts, so that the hammer will not be injured. They were formerly made square when nail heads were square, but now round ones are common. To obviate slipping, some have "cup points," that is, with a concave tip, and some spur points.

Fig. 165. Using a Nailset.

To keep the nailset in its place on the nail-head it may be held closely against the third finger of the left hand, which rests on the wood close to the nail. When a nailset is lacking, the head of a brad, held nearly flat, may be used. But care is necessary to avoid bruising the wood.

6. HOLDING TOOLS

A. Tools for Holding Work

The advance in ease of handworking may largely be measured by the facilities for holding materials or other tools. The primitive man used no devices for holding except his hands and feet. The Japanese, who perhaps are the most skilful of joiners, still largely use their fingers and toes. On the other hand, Anglo-Saxons have developed an enormous variety of methods for holding work and tools.

Fig. 166. Bench made with Pinned Mortise-and-Tenon Joints, Low Back.

Fig. 167. Woodworking Bench used at Pratt Institute, Showing Self-Adjusting Upright Vise.

Benches. The essential features of a work-bench are a firm, steady table with a vise and places for tools. The joints are either pinned or wedged mortise-and-tenon, or draw-bolt joints. The best benches are made of maple, the tops being strips joined or tongued-and-grooved together. It is common also to have a trough at the back of the top of the bench, i. e., a space 6" or 8" wide, set lower than the upper surface, in which tools may be placed so as not to roll off. A low pillow, fastened at the left hand end of the trough, on which to set planes in order that the edge of the cutter may not be injured, is an advantage. The tool-rack is of capital importance. It has been common in school benches to affix it to a board, which rises considerably above the top of the bench, Fig. 169, but a better plan is to have the top of it no higher than the bench-top, Fig. 166. Then the light on the bench is not obscured, and when a flat top is needed for large work it can readily be had by removing the tools. Elaborate benches with lock drawers are also much used in the shops of large city schools.

Fig. 168. A Rapid-Acting Vise.

Vises for holding wood are of three general styles, (1) those with an upright wooden jaw, Fig. 167, which holds wide pieces of work well. They are now made with an automatic adjusting device by which the jaw and the face of the bench are kept parallel; (2) wooden vises with a horizontal jaw, guided by parallel runners, Fig. 166, and, (3) metal rapid-acting vises, Fig. 168. The latter are the most durable and in most respects more convenient. Special vises are also made for wood-carvers, for saw-filing, etc.

Fig. 169. Holding a Large Board in Vise for Planing.

The best woodworking benches are equipped with both side- and tail-vises. The tail-vise is supplemented by movable bench-stops for holding pieces of different lengths. In planing the side of a board it is held in place between the tail-vise and one of the bench-stops. A board should not be squeezed sidewise between the jaws of a vise when it is to be planed, lest it be bent out of shape. In planing the edge of a board it is ordinarily held in the side-vise. A long board, one end of which is in the vise, may also need to be supported at the other end. This may be done by clamping to it a handscrew, the jaw of which rests on the top of the bench, Fig. 169. When the vise is likely to be twisted out of square by the insertion of a piece of wood at one end of it, it is well to insert another piece of equal thickness at the other end of the vise to keep it square, as in Fig. 120, p. 82. In this case, (Fig. 120,) the extra piece also supports the piece being worked upon.

The vise is also of great use in carrying on many other processes, but a good workman does not use it to the exclusion of the saw-horse and bench-hook.

Horses are of great use both for the rough sawing of material and in supporting large pieces during the process of construction. The common form is shown in Fig. 170, but a more convenient form for sawing has an open top, as in Fig. 171.

Fig. 170. Saw-Horse.

Fig. 171. Saw-Horse.

The picture-frame-vise, Fig. 172, is a very convenient tool for making mitered joints, as in picture-frames. The vise holds two sides firmly so that after gluing they may be either nailed together or a spline inserted in a saw cut previously made. See Fig. 268, No. 55, p. 181. If the last joint in a picture-frame does not quite match, a kerf may be sawn at the junction of the two pieces, which can then be drawn close together.

Fig. 172. Picture-Frame-Vise.

Handscrews, Fig. 173, consist of four parts, the shoulder jaw and the screw jaw, made of maple, and the end spindle and the middle spindle, made of hickory. The parts when broken can be bought separately. Handscrews vary in size from those with jaws four inches long to those with jaws twenty-two inches long. The best kind are oiled so that glue will not adhere to them. In adjusting the jaws, if the handle of the middle spindle is held in one hand, and the handle of the end spindle in the other hand, and both are revolved together, the jaws may be closed or opened evenly, Fig. 174. In use care must be taken to keep the jaws parallel, in order to obtain the greatest pressure and to prevent the spindles from being broken. It is always important to have the jaws press on the work evenly. To secure this, the middle spindle should be tightened first, and then the end spindle. Handscrews are convenient for a great variety of uses, as clamping up glued pieces, holding pieces together temporarily for boring, Fig. 247, p. 152, holding work at any desired angle in the vise, as for chamfering or beveling, Fig. 175, etc.

Fig. 173. Handscrew.

Fig. 174. Adjusting Handscrew.

Fig. 175. Using a Handscrew to hold a Board at an Angle.

Clamps are made of both wood and iron, the most satisfactory for speed, strength, and durability are steel-bar carpenter clamps, Fig. 176. They vary in length from 1½ ft. to 8 ft. The separate parts are the steel bar A, the cast-iron frame B, the tip C into which fits the screw D, on the other end of which is the crank E, and the slide F with its dog G, which engages in the notches on the bar. Any part, if broken, can be replaced separately.

Fig. 176. Steel-Bar Carpenter's Clamp. a. Steel Bar. b. Frame. c. Tip. d. Screw. e. Crank. f. Slide. g. Dog.

Iron Handscrews, also called C clamps and carriage-makers' clamps. Fig. 177, are useful in certain kinds of work, as in gluing in special places and in wood-carving. All iron clamps need blocks of soft wood to be placed between them and the finished work.

Fig. 177. Iron Handscrew, (Carriage-Maker's Clamp).

Pinch-dogs, Fig. 178, are a convenient device for drawing together two pieces of wood, when injury to the surfaces in which they are driven does not matter. They vary in size from ¾" to 2¾". For ordinary purposes the smallest size is sufficient. For especially fine work, double-pointed tacks, properly filed, are convenient.

Fig. 178. Pinch-Dog.

The bench-hook, Fig. 179, is a simple device for holding firmly small pieces of work when they are being sawn, chisled, etc. It also saves the bench from being marred. The angles should be kept exactly square.

Fig. 179. Bench-Hook.

The miter-box, Fig. 180, is a similar device with the addition of a guide for the saw. The iron miter-box, Fig. 181, with the saw adjustable to various angles, insures accurate work.

Fig. 180. Miter-Box.

Fig. 181. Iron Miter-Box.

Such tools as pliers, Fig. 182, pincers, Fig. 183, and nippers, Fig. 184, made for gripping iron, are often useful in the woodworking shop. So are various sorts of wrenches; as fixed, socketed, adjustable, monkey- and pipe-wrenches.

B. Tools for holding other tools

The brace or bit-stock, Fig. 185, holds all sorts of boring tools as well as screwdrivers, dowel-pointers, etc. The simple brace or bit-stock consists of a chuck, a handle, and a knob, and is sufficient for ordinary use; but the ratchet-brace enables the user to bore near to surfaces or corners where a complete sweep cannot be made. It is also useful where sufficient power can be applied only at one part of the sweep. By means of pawls which engage in the ratchet-wheel, the bit can be turned in either direction at the will of the user. The size of the brace is indicated by the "sweep," that is, the diameter of the circle thru which the swinging handle turns. To insert a bit or other tool, Fig. 186, grasp firmly with one hand the sleeve of the chuck pointing it upward, and revolve the handle with the other hand, unscrewing the sleeve until the jaws open enough to admit the whole tang of the bit. Then reverse the motion and the bit will be held tightly in place. Various hand-, breast-, bench-, bow-drills and automatic drills are of use in doing quick work and for boring small holes, Fig. 187.

Fig. 185. Ratchet-Brace.

Fig. 186. Inserting a Bit in Stock.

Fig. 187. Hand-Drill.

The screwdriver, Fig. 188, is a sort of holding tool for turning, and so driving screws. Various devices have been tried to prevent the twisting in the handle. This is now practically assured in various makes. The other important matter in a screwdriver is that the point be of the right temper, so as neither to bend nor to break. If the corners break they can be reground, but care should be taken not to make the angle too obtuse or the driver will slip out of the slot in the screw-head. The bevel should have a long taper. A shop should be equipped with different sizes of screwdrivers to fit the different sizes of screws. Screwdrivers vary in size, the shank ranging in length from 2½" to 18". A long screwdriver is more powerful than a short one, for the screwdriver is rarely exactly in line with the axis of the screw, but the handle revolves in a circle. This means an increased leverage, so that the longer the screwdriver, the greater the leverage.

For heavy work, screwdriver-bits, Fig. 189, in a bit-stock are useful, and for quick work, the spiral screwdriver, Fig. 190, and for small work, the ratchet-screwdriver.

7. MEASURING AND MARKING TOOLS

It is a long step from the time when one inch meant the width of the thumb, and one foot meant the length of the foot, to the measuring of distances and of angles which vary almost infinitesimally. No such accuracy is necessary in measuring wood as in measuring metal, but still there is a considerable variety of tools for this purpose.

For measuring distances, the rule, Fig. 191, is the one in most common use. It is usually made of boxwood. For convenience it is hinged so as to fold. A rule is called "two-fold" when it is made of two pieces, "four-fold" when made of four pieces, etc. When measuring or marking from it, it can be used more accurately by turning it on edge, so that the lines of the graduations may come directly against the work. The one in most common use in school shops, is a two-foot, two-fold rule. Some instructors prefer to have pupils use a four-fold rule, because that is the form commonly used in the woodworking trades. Steel bench-rules, Fig. 192, are satisfactory in school work because unbreakable and because they do not disappear so rapidly as pocket rules. They need to be burnished occasionally.

Fig. 191. Two-Foot Rule. Two Fold.

Fig. 192. Steel Bench-Rule.

The steel square, Figs. 193, 194, 196, 197, is useful, not only as a straight-edge and try-square, but also for a number of graduations and tables which are stamped on it. There are various forms, but the one in most common use consists of a blade or "body" 24" × 2" and a "tongue," 16" × 1½", at right angles to each other. Sargent's trade number for this form is 100. It includes graduations in hundredths, thirty-seconds, sixteenths, twelfths, tenths, and eighths of an inch, also a brace-measure, an eight-square measure, and the Essex board-measure. Another style, instead of an Essex board-measure, and the hundredths graduation has a rafter-table. The side upon which the name of the maker is stamped, is called the "face," and the reverse side the "back."

The brace-measure is to be found along the center of the back of the tongue, Fig. 193. It is used thus: the two equal numbers set one above the other represent the sides of a square, and the single number to their right, represents in inches and decimals, the diagonal of that square.

For determining the length of the long side (hypothenuse) of a right angle triangle, when the other two given sides are not equal, the foot rule, or another steel square may be laid diagonally across the blade and arm, and applied directly to the proper graduations thereon, and the distance between them measured on the rule. If the distance to be measured is in feet, use the ¹⁄12" graduations on the back of the square.

Fig. 193. Back of Steel Square, Brace Measure.

Fig. 194. Face of Steel Square, Octagon, "Eight-Square," Scale.

To use the octagonal (or 8-square) scale, Fig. 194, which is along the center of the face of the tongue, with the dividers, take the number of spaces in the scale to correspond with the number of inches the piece of wood is square, and lay this distance off from the center point, on each edge of the board. Connect the points thus obtained, diagonally across the corners, and a nearly exact octagon will be had. E.g., on a board 12" square, Fig. 195, find A.B.C.D., the centers of each edge. Now with the dividers take 12 spaces from the 8-square scale. Lay off this distance on each side as A' A" from A, B' B" from B, etc. Now connect A" with B', B" with C', C" with D', D" with A', and the octagon is obtained.

Fig. 195. Method of Using the Eight-Square Scale on the Steel-Square.

In making a square piece of timber octagonal, the same method is used on the butt, sawed true. When the distance from one center is laid off, the marking-gage may be set to the distance from the point thus obtained to the corner of the timber, and the piece gaged from all four corners both ways. Cutting off the outside arrises to the gaged lines leaves an octagonal stick.

The board-measure is stamped on the back of the blade of the square, Fig. 196. The figure 12 on the outer edge of the blade is the starting point for all calculations. It represents a 1" board, 12" wide, and the smaller figures under it indicate the length of boards in feet. Thus a board 12" wide, and 8' long measures 8 square feet and so on down the column. To use it, for boards other than 12" wide:—find the length of the board in feet, under the 12" marked on the outer edge of the blade, then run right or left along that line to the width of the board in inches. The number under the width in inches on the line showing the length in feet, gives the board feet for lumber 1" thick.

For example, to measure a board 14' long, and 11" wide,—under the figure 12, find 14 (length of the board); to the left of this, under 11 is the number 12.10; 12' 10" is the board-measure of the board in question. Since a board 12' long would have as many board feet in it as it is inches wide, the B. M. is omitted for 12' boards. Likewise a board 6' long would have ½ the number of board feet that it is inches wide. If the board is shorter than the lowest figure given (8) it can be found by dividing its double by 2.; e. g., to measure a board 5' long and 9" wide, take 10 under the 12, run to the left of the number under 9, which is 7' 6"; ½ of this would be 3' 9", the number of board feet in the board.