Fig. 132.Fig. 132.
Shadows From a Solid Body.—We can understand this better by examining Fig. 129, which shows a vertical board, and a beam of light (A) passing downwardly beyond the upper margin of the board. Under these conditions the upper margin of the board appears darker to the vision, by contrast, than the lower part. It should also be understood that, in general, the nearer the object the lighter it is, so that as the upper edge of the board is farthest from the eye the heavy shading there will at least give the appearance of distance to that edge.
But suppose that instead of having the surface of the board flat, it should be concaved, as in Fig. 130, it is obvious that the hollow, or the concaved, portion of the board must intensify the shadows or the darkness at the upper edge. This explains why the heavy shading in Fig. 126 is at that upper margin.
Flat Effects.—If the board is flat it may be shaded, as shown in Fig. 131, in which the lines are all of the same thickness, and are spaced farther and farther apart at regularly increasing intervals.
Fig. 133.Fig. 134.Fig. 133.Fig. 134.
Fig. 133.
Fig. 134.
The Direction of Light.—Now, in drawing, we must observe another thing. Not only does the light always come from above, but it comes also from the left side. I show in Fig. 132 two squares, one within the other. All the lines are of the same thickness. Can you determine by means of such a drawing what the inner square represents? Is it a block, or raised surface, or is it a depression?
Raised Surfaces.—Fig. 133 shows it in the form of a block, simply by thickening the lower and the right-hand lines.
Depressed Surfaces.—If, by chance, you should make the upper and the left-hand lines heavy, as in Fig. 134, it would, undoubtedly, appear depressed, and would need no further explanation.
Full Shading,—But, in order to furnish an additional example of the effect of shading, suppose we shade the surface of the large square, as shown in Fig. 135, and you will at once see that not only is the effect emphasized, but it all the more clearly expresses what you want to show. In like manner, in Fig. 136, we shade only the space within the inner square, and it is only too obvious how shadows give us surface conformation.
Fig. 135.Fig. 136.Fig. 135.Fig. 136.
Fig. 135.
Fig. 136.
Illustrating Cube Shading.—In Fig. 137 I show merely nine lines joined together, all lines being of equal thickness.
As thus drawn it may represent, for instance,a cube, or it may show simply a square base (A) with two sides (B, B) of equal dimensions.
Shading Effects.—Now, to examine it properly so as to observe what the draughtsman wishes to express, look at Fig. 138, in which the three diverging lines (A, B, C) are increased in thickness, and the cube appears plainly. On the other hand, in Fig. 139, the thickening of the lines (D, E, F) shows an entirely different structure.
Fig. 137.Fig. 137.
Fig. 138.Fig. 139.Fig. 138.Fig. 139.
Fig. 138.
Fig. 139.
It must be remembered, therefore, that to show raised surfaces the general direction is to shade heavily the lower horizontal and the right vertical lines. (See Fig. 133.)
Heavy Lines.—But there is an exception to this rule. See two examples (Fig. 140). Here two parallellines appear close together to form the edge nearest the eye. In such cases the second, or upper, line is heaviest. On vertical lines, as in Fig. 141, the second line from the right is heaviest. These examples show plain geometrical lines, and those from Figs. 138 to 141, inclusive, are in perspective.
Fig. 140.Fig. 141.Fig. 140.Fig. 141.
Fig. 140.
Fig. 141.
Perspective.—A perspective is a most deceptive figure, and a cube, for instance, may be drawn so that the various lines will differ in length, and also be equidistant from each other. Or all the lines may be of the same length and have the distances between them vary. Supposing we have two cubes, one located above the other, separated, say, two feet or more from each other. It is obvious that the lines of the two cubes will not be the same to a camera, because, if they were photographed, they would appear exactly as they are, so far as their positions are concerned, and not as they appear. But the cubes do appear to the eyeas having six equal sides. The camera shows that they do not have six equal sides so far as measurement is concerned. You will see, therefore, that the position of the eye, relative to the cube, is what determines the angle, orthe relativeangles of all the lines.
Fig. 142.Fig. 142.
Fig. 143.Fig. 143.
A True Perspective of a Cube.—Fig. 142 shows a true perspective—that is, it is true from the measurement standpoint. It is what is called anisometricalview, or a figure in which all the lines not only are of equal length, but the parallel lines areall spaced apart the same distances from each other.
Isometric Cube.—I enclose this cube within a circle, as in Fig. 143. To form this cube the circle (A) is drawn and bisected with a vertical line (B). This forms the starting point for stepping off the six points (C) in the circle, using the dividers without resetting, after you have made the circle. Then connect each of the points (C) by straight lines (D). These lines are called chords. From the center draw two lines (E) at an angle and one line (F) vertically. These are the radial lines. You will see from the foregoing that the chords (D) form the outline of the cube—or the lines farthest from the eye, and the radial lines (E, F) are the nearest to the eye. In this position we are looking at the block at a true diagonal—that is, from a corner at one side to the extreme corner on the opposite side.
Fig. 144.Fig. 144.
Let us contrast this, and particularly Fig. 142,with the cube which is placed higher up, viewed from the same standpoint.
Flattened Perspective.—Fig. 144 shows the new perspective, in which the three vertical lines (A, A, A) are of equal length, and the six angularly disposed lines (B, C) are of equal length, but shorter than the lines A. The only change which has been made is to shorten the distance across the corner from D to D, but the vertical lines (A) are the same in length as the corresponding lines in Fig. 143. Notwithstanding this change the cubes in both figures appear to be of the same size, as, in fact, they really are.
Fig. 145.Fig. 145.
In forming a perspective, therefore, it would be a good idea for the boy to have a cube of wood always at hand, which, if laid down on a horizontal support, alongside, or within range of the object tobe drawn, will serve as a guide to the perspective.
Technical Designations.—As all geometrical lines have designations, I have incorporated such figures as will be most serviceable to the boy, each figure being accompanied by its proper definition.
Fig. 146.Fig. 147.Fig. 146.Fig. 147.
Fig. 146.
Fig. 147.
Before passing to that subject I can better show some of the simple forms by means of suitable diagrams.
Referring to Fig. 145, let us direct our attention to the body (G), formed by the line (D) across the circle. This body is called a segment. A chord (D) and a curve comprise a segment.
Sector and Segment.—Now examine the shape of the body formed by two of the radial lines (E, E) and that part of the circle which extends from one radial line to the other. The body thus formed is a sector, and it is made by two radiating lines and a curved line. Learn to distinguish readily, in your mind, the difference between the two figures.
Terms of Angles.—The relation of the lines to each other, the manner in which they are joined together, and their comparative angles, all have special terms and meanings. Thus, referring to the isometric cube, in Fig. 145, the angle formed at the center by the lines (B, E) is different from the angle formed at the margin by the lines (E, F). The angle formed by B, E is called an exterior angle; and that formed by E, F is an interior angle. If you will draw a line (G) from the center to the circle line, so it intersects it at C, the lines B, D, G form an equilateral or isosceles triangle; if you draw a chord (A) from C to C, the lines H, E, F will form an obtuse triangle, and B, F, H a right-angled triangle.
Circles and Curves.—Circles, and, in fact, all forms of curved work, are the most difficult for beginners. The simplest figure is the circle, which, if it represents a raised surface, is provided with a heavy line on the lower right-hand side, as in Fig. 146; but the proper artistic expression is shown in Fig. 147, in which the lower right-hand side is shaded in rings running only a part of the way around, gradually diminishing in length, and spaced farther and farther apart as you approach the center, thus giving the appearance of a sphere.
Fig. 148.Fig. 148.
Irregular Curves.—But the irregular curves require the most care to form properly. Let us tryfirst the elliptical curve (Fig. 148). The proper thing is, first, to draw a line (A), which is called the "major axis." On this axis we mark for our guidance two points (B, B). With the dividers find a point (C) exactly midway, and draw a cross line (D). This is called the "minor axis." If we choose to do so we may indicate two points (E, E) on the minor axis, which, in this case, for convenience, are so spaced that the distance along the major axis, between B, B, is twice the length across the minor axis (D), along E, E. Now find one-quarter of the distance from B to C, as at F, and with a compass pencil make a half circle (G). If, now, you will set the compass point on the center mark (C), and the pencil point of the compass on B, and measure along the minor axis (D) on bothsides of the major axis, you will make two points, as at H. These points are your centers for scribing the long sides of the ellipse. Before proceeding to strike the curved lines (J), draw a diagonal line (K) from H to each marking point (F). Do this on both sides of the major axis, and produce these lines so they cross the curved lines (G). When you ink in your ellipse do not allow the circle pen to cross the lines (K), and you will have a mechanical ellipse.
Ellipses and Ovals.—It is not necessary to measure the centering points (F) at certain specified distances from the intersection of the horizontal and vertical lines. We may take any point along the major axis, as shown, for instance, in Fig. 149. Let B be this point, taken at random. Then describe the half circle (C). We may, also, arbitrarily, take any point, as, for instance, D on the minor axis E, and by drawing the diagonal lines (F) we find marks on the circle (C), which are the meeting lines for the large curve (H), with the small curve (C). In this case we have formed an ovate or an oval form. Experience will soon make perfect in following out these directions.
Focal Points.—The focal point of a circle is its center, and is called thefocus. But an ellipse has two focal points, calledfoci, represented by F, F in Fig. 148, and by B, B in Fig. 149.
Aproduced lineis one which extends out beyond the marking point. Thus in Fig. 148 that part of the line K between F and G represents the produced portion of line K.
Fig. 149.Fig. 149.
Spirals.—There is no more difficult figure to make with a bow or a circle pen than a spiral. In Fig. 150 a horizontal and a vertical line (A, B), respectively, are drawn, and at their intersection a small circle (C) is formed. This now provides for four centering points for the circle pen, on the two lines (A, B). Intermediate these points indicate a second set of marks halfway between the marks on the lines. If you will now set the point of the compass at, say, the mark 3, and the pencil point of the compass at D, and make a curved mark one-eighth of the way around, say, to the radial line (E), then put the point of thecompass to 4, and extend the pencil point of the compass so it coincides with the curved line just drawn, and then again make another curve, one-eighth of a complete circle, and so on around the entire circle of marking points, successively, you will produce a spiral, which, although not absolutely accurate, is the nearest approach with a circle pen. To make this neatly requires care and patience.
Fig. 150.Fig. 150.
Perpendicular and Vertical.—A few words now as to terms. The boy is often confused in determining the difference betweenperpendicularandvertical. There is a pronounced difference. Vertical means up and down. It is on a line in the direction a ball takes when it falls straight toward the center of the earth. The wordperpendicular, as usually employed in astronomy, means the same thing, but in geometry, or in drafting, or in its use in the arts it means that a perpendicularline is at right angles to some other line. Suppose you put a square upon a roof so that one leg of the square extends up and down on the roof, and the other leg projects outwardly from the roof. In this case the projecting leg isperpendicularto the roof. Never use the wordverticalin this connection.
Signs to Indicate Measurements.—The small circle (°) is always used to designatedegree. Thus 10° means ten degrees.
Feet are indicated by the single mark '; and two closely allied marks " are for inches. Thus five feet ten inches should be written 5' 10". A large cross (×) indicates the word "by," and in expressing the term six feet by three feet two inches, it should be written 6' × 3'2".
The foregoing figures give some of the fundamentals necessary to be acquired, and it may be said that if the boy will learn the principles involved in the drawings he will have no difficulty in producing intelligible work; but as this is not a treatise on drawing we cannot go into the more refined phases of the subject.
Definitions.—The following figures show the various geometrical forms and their definitions:
Fig. 151.-Fig. 165.
151.Abscissa.—The point in a curve, A, which is referred to by certain lines, such as B, which extend out from an axis, X, or the ordinate line Z.
152.Angle.—The inclosed space near the point where two lines meet.
153.Apothegm.—The perpendicular line A from the center to one side of a regular polygon. It represents the radial line of a polygon the same as the radius represents half the diameter of a circle.
154.ApsidesorApsis.—One of two points, A, A, of an orbit, oval or ellipse farthest from the axis, or the two small dots.
155.Chord.—A right line, as A, uniting the extremities of the arc of a circle or a curve.
156.Convolute(see alsoInvolute).—Usually employed to designate a wave or folds in opposite directions. A double involute.
157.Conic Section.—Having the form of or resembling a cone. Formed by cutting off a cone at any angle. See line A.
158.Conoid.—Anything that has a form resembling that of a cone.
159.Cycloid.—A curve, A, generated by a point, B, in the plane of a circle or wheel, C, when the wheel is rolled along a straight line.
160.Ellipsoid.—A solid, all plane sections of which are ellipses or circles.
161.Epicycloid.—A curve, A, traced by a point, B, in the circumference of a wheel, C, which rolls on the convex side of a fixed circle, D.
162.Evolute.—A curve, A, from which another curve, like B, on each of the inner ends of the lines C is made. D is a spool, and the lines C represent a thread at different positions. The thread has a marker, E, so that when the thread is wound on the spool the marker E makes the evolute line A.
163.Focus.—The center, A, of a circle; also one of the two centering points, B, of an ellipse or an oval.
164.Gnome.—The space included between the boundary lines of two similar parallelograms, the one within the other, with an angle in common.
165.Hyperbola.—A curve, A, formed by the section of a cone. If the cone is cut off vertically on the dotted line, A, the curve is a hyperbola. SeeParabola.
Fig. 167.-Fig. 184.
167.Hypothenuse.—The side, A, of a right-angled triangle which is opposite to the right angle B, C. A, regular triangle; C, irregular triangle.
168.Incidence.—The angle, A, which is the same angle as, for instance, a ray of light, B, which falls on a mirror, C. The line D is the perpendicular.
169.Isosceles Triangle.—Having two sides or legs, A, A, that are equal.
170.Parabola.—One of the conic sections formed by cutting of a cone so that the cut line, A, is not vertical. SeeHyperbolawhere the cut line is vertical.
171.Parallelogram.—A right-lined quadrilateral figure, whose opposite sides, A, A, or B, B, are parallel and consequently equal.
172.Pelecoid.—A figure, somewhat hatchet-shaped, bounded by a semicircle, A, and two inverted quadrants, and equal to a square, C.
173.Polygons.—Many-sided and many with angles.
174.Pyramid.—A solid structure generally with a square base and having its sides meeting in an apex or peak. The peak is the vertex.
175.Quadrant.—The quarter of a circle or of the circumference of a circle. A horizontal line, A, and a vertical line, B, make the four quadrants, like C.
176.Quadrilateral.—A plane figure having four sides, and consequently four angles. Any figure formed by four lines.
177.Rhomb.—An equilateral parallelogram or a quadrilateral figure whose sides are equal and the opposite sides, B, B, parallel.
178.Sector.—A part, A, of a circle formed by two radial lines, B, B, and bounded at the end by a curve.
179.Segment.—A part, A, cut from a circle by a straight line, B. The straight line, B, is the chord or thesegmental line.
180.Sinusoid.—A wave-like form. It may be regular or irregular.
181.Tangent.—A line, A, running out from the curve at right angles from a radial line.
182.Tetrahedron.—A solid figure enclosed or bounded by four triangles, like A or B. A plain pyramid is bounded by five triangles.
183.Vertex.—The meeting point, A, of two or more lines.
184.Volute.—A spiral scroll, used largely in architecture, which forms one of the chief features of the Ionic capital.
Moldings.—The use of moldings was early resorted to by the nations of antiquity, and we marvel to-day at many of the beautiful designs which the Phœnecians, the Greeks and the Romans produced. If you analyze the lines used you will be surprised to learn how few are the designs which go to make up the wonderful columns, spires, minarets and domes which are represented in the various types of architecture.
The Basis of Moldings.—Suppose we take the base type of moldings, and see how simple they are and then, by using these forms, try to build up or ornament some article of furniture, as an example of their utility.
The Simplest Molding.—In Fig. 185 we show a molding of the most elementary character known, being simply in the form of a band (A) placed below the cap. Such a molding gives to the article on which it is placed three distinct lines, C, D and E, If you stop to consider you will note that the molding, while it may add to the strength of the article, is primarily of servicebecause the lines and surfaces produce shadows, and therefore become valuable in an artistic sense.
The Astragal.—Fig. 186 shows the ankle-bone molding, technically called theAstragal. This form is round, and properly placed produces a good effect, as it throws the darkest shadow of any form of molding.
Fig. 185.Fig. 188.Fig. 185.Fig. 186.
Fig. 185.
Fig. 186.
Fig. 187.Fig. 188.Fig. 187.Fig. 188.
Fig. 187.
Fig. 188.
The Cavetto.—Fig. 187 is the cavetto, or round type. Its proper use gives a delicate outline, but it is principally applied with some other form of molding.
The Ovolo.—Fig. 188, called the ovolo, is a quarter round molding with the lobe (A) projecting downwardly. It is distinguished fromthe astragal because it casts less of a shadow above and below.
The Torus.—Fig. 189, known as the torus, is a modified form of the ovolo, but the lobe (A) projects out horizontally instead of downwardly.
The Apophyges(Pronounced apof-i-ges).—Fig. 190 is also called thescape, and is a concaved type of molding, being a hollowed curvature used on columns where its form causes a merging of the shaft with the fillet.
Fig. 189.Fig. 190.Fig. 189. Torus.Fig. 190. Apophyge.Fig. 28.Fig. 192.Fig. 191. Cymatium.Fig. 192. Ogee-Recta.
Fig. 189. Torus.
Fig. 190. Apophyge.
Fig. 191. Cymatium.
Fig. 192. Ogee-Recta.
The Cymatium.—Fig. 191 is the cymatium (derived from the word cyme), meaning wave-like. This form must be in two curves, one inwardly and one outwardly.
The Ogee.—Fig. 192, called the ogee, is the most useful of all moldings, for two reasons: First, it may have the concaved surface uppermost, in which form it is called ogee recta—that is, rightside up; or it may be inverted, as in Fig. 193, with the concaved surface below, and is then called ogee reversa. Contrast these two views and you will note what a difference the mere inversion of the strip makes in the appearance. Second, because the ogee has in it, in a combined form, the outlines of nearly all the other types. The only advantage there is in using the other types is because you may thereby build up and space your work better than by using only one simple form.
Fig. 193. Ogee-Reversa.Fig. 193. Ogee-Reversa.
Fig. 194. Bead or Reedy.Fig. 194. Bead or Reedy.
You will notice that the ogee is somewhat like the cymatium, the difference being that the concaved part is not so pronounced as in the ogee, and the convexed portion bulges much further than in the ogee. It is capable of use with other moldings, and may be reversed with just as good effect as the ogee.
The Reedy.—Fig. 194 represents the reedy, or the bead—that is, it is made up of reeds. It is a type of molding which should not be used with any other pronounced type of molding.
The Casement(Fig. 195).—In this we have a form of molding used almost exclusively at the base of structures, such as columns, porticoes and like work.
Fig. 195. Casement.Fig. 195. Casement.
Now, before proceeding to use these moldings, let us examine a Roman-Doric column, one of the most famous types of architecture produced. We shall see how the ancients combined moldings to produce grace, lights and shadows and artistic effects.
The Roman-Doric Column.—In Fig. 196 is shown a Roman-Doric column, in which the cymatium, the ovolo, cavetto, astragal and the ogee are used, together with the fillets, bases and caps, and it is interesting to study this because of its beautiful proportions.
Fig. 196.Fig. 196.
The pedestal and base are equal in vertical dimensions to the entablature and capital. The entablature is but slightly narrower than the pedestal;and the length of the column is, approximately, four times the height of the pedestal. The base of the shaft, while larger diametrically than the capital, is really shorter measured vertically. There is a reason for this. The eye must travel a greater distance to reach the upper end of the shaft, and is also at a greater angle to that part of the shaft, hence it appears shorter, while it is in reality longer. For this reason a capital must be longer or taller than the base of a shaft, and it is also smaller in diameter.
It will be well to study the column not only on account of the wonderful blending of the various forms of moldings, but because it will impress you with a sense of proportions, and give you an idea of how simple lines may be employed to great advantage in all your work.
Lessons from the Doric Column.—As an example, suppose we take a plain cabinet, and endeavor to embellish it with the types of molding described, and you will see to what elaboration the operation may be carried.
Applying Molding.—Let Fig. 197 represent the front, top and bottom of our cabinet; and the first thing we shall do is to add a base (A) and a cap (B). Now, commencing at the top, suppose we utilize the simplest form of molding, the band.
This we may make of any desired width, asshown in Fig. 198. On this band we can apply the ogee type (Fig. 199) right side up.
But for variation we may decide to use the ogee reversed, as in Fig. 200. This will afford us something else to think about and will call upon our powers of initiative in order to finish off the lower margin or edge of the ogee reversa.
Fig. 197.Fig. 197.
Fig. 198.Fig. 199.Fig. 198.Fig. 199.
Fig. 198.
Fig. 199.
If we take the ogee recta, as shown in Fig. 201, we may use the cavetto, or the ovolo (Fig. 202); but if we use the ogee reversa we must use a convex molding like the cavetto at one base, anda convex molding, like the torus or the ovolo, at the other base.
In the latter (Fig. 202) four different moldings are used with the ogee as the principal structure.
Base Embellishments.—In like manner (Fig. 204) the base may have the casement type first attached in the corner, and then the ovolo, or the astragal added, as in Fig. 203.
Fig. 200.Fig. 201.Fig. 202.Fig. 200.Fig. 201.Fig. 202.
Fig. 200.
Fig. 201.
Fig. 202.
Straight-faced Moldings.—Now let us carry the principle still further, and, instead of using various type of moldings, we will employ nothing but straight strips of wood. This treatment will soon indicate to you that the true mechanic or artisan is he who can take advantage of whatever he finds at hand.
Let us take the same cabinet front (Fig. 205), and below the cap (A) place a narrow strip (B), the lower corner of which has been chamfered off, as at C. Below the strip B is a thinner strip (D), vertically disposed, and about two-thirds its width. The lower corner of this is also chamfered, as atF. To finish, apply a small strip (G) in the corner, and you have an embellished top that has the appearance, from a short distance, of being made up of molding.
Plain Molded Base.—The base may be treated in the same manner. The main strip (4) has its upper corner chamfered off, as at I, and on this is nailed a thin, narrow finishing strip (J). The upper part or molded top, in this case, has eleven distinct lines, and the base has six lines. By experimenting you may soon put together the most available kinds of molding strips.
Fig. 203.Fig. 204.Fig. 203.Fig. 204.
Fig. 203.
Fig. 204.
Diversified Uses.—For a great overhang you may use the cavetto, or the apophyges, and below that the astragal or the torus; and for the base the casement is the most serviceable molding, and it may be finished off with the ovolo or the cymatium.
Pages of examples might be cited to show the variety and the diversification available with different types.
Shadows Cast by Moldings.—Always bear in mind that a curved surface makes a blended shadow. A straight, flat or plain surface does not, and it is for that reason the concaved and the convexed surfaces, brought out by moldings, become so important.
Fig. 205.Fig. 205.
A little study and experimenting will soon teach you how a convex, a concave or a flat surface, and a corner or corners should be arranged relatively to each other; how much one should project beyond the other; and what the proportional widths of the different molding bands should be. An entire volume would scarcely exhaust this subject.
In the chapter on How Work is Laid Out, an example was given of the particular manner pursued in laying out mortises and tenons, and also dovetailed work. I deem it advisable to add some details to the subject, as well as to direct attention to some features which do not properly belong to the laying out of work.
Where Mortises Should Be Used.—Most important of all is a general idea of places and conditions under which mortises should be resorted to. There are four ways in which different members may be secured to each other. First, by mortises and tenons; second, by a lap-and-butt; third, by scarfing; and, fourth, by tonguing and grooving.
Depth of Mortises.—When a certain article is to be made, the first consideration is, how the joint or joints shall be made. The general rule for using the tenon and mortise is where two parts are joined wherein the grains of the twomembers run at right angles to each other, as in the following figure.
Rule for Mortises.—Fig. 206 shows such an example. You will notice this in doors particularly, as an example of work.
Fig. 206.Fig. 206.
Fig. 207.Fig. 207.
The next consideration is, shall the mortises be cut entirely through the piece? This is answered by the query as to whether or not the end of the tenon will be exposed; and usually, if a smooth finish is required, the mortise should not go through the member. In a door, however, the tenons are exposed at the edges of the door, and are, therefore, seen, so that we must apply some other rule. The one universally adopted is, that where, as in a door stile, it is broad and comparatively thin, or where the member having the mortisein its edge is much thinner than its width, the mortise should go through from edge to edge.
The reason for this lies in the inability to sink the mortises through the stile (A, Fig. 207) perfectly true, and usually the job is turned out something like the illustration shows. The side of the rail (B) must be straight with the side of the stile. If the work is done by machinery it results in accuracy unattainable in hand work.
Fig. 208.Fig. 208.
True Mortise Work.—The essense of good joining work is the ability to sink the chisel true with the side of the member. More uneven work is produced by haste than by inability. The tendencyof all beginners is to strike the chisel too hard, in order the more quickly to get down to the bottom of the mortise. Hence, bad work follows.
Steps in Cutting Mortises.—Examine Fig. 208, which, for convenience, gives six successive steps in making the mortise. The marksa,bdesignate the limits, or the length, of the mortise. The chisel (C) is not started at the marking line (A), but at least an eighth of an inch from it. The first cut, as at B, gives a starting point for the next cut or placement of the chisel. When the second cut (B) has thus been made, the chisel should be turned around, as in dotted lined, position C, thereby making a finish cut down to the bottom of the mortise, linee, so that when the fourth cut has been made along linef, we are ready for the fifth cut, position C; then the sixth cut, position D, which leaves the mortise as shown at E. Then turn the chisel to the position shown at F, and cut down the last end of the mortise square, as shown in G, and clean out the mortise well before making the finishing cuts on the marking lines (a,b). The particular reason for cleaning out the mortise before making the finish cuts is, that the corners of the mortise are used as fulcrums for the chisels, and the eighth of an inch stock still remaining protects the corners.
Things to Avoid in Mortising.—You must be careful to refrain from undercutting as your chisel goes down at the linesa,b, because if you commit this error you will make a bad joint.
As much care should be exercised in producing the tenon, although the most common error is apt to occur in making the shoulder. This should be a trifle undercut.
Fig. 209.Fig. 209.
See the lines (A, Fig. 209), which illustrate this.
Lap-and-Butt Joint.—The lap-and-butt is the form of uniting members which is most generally used to splice together timbers, where they join each other end to end.
Fig. 210.Fig. 210.
Bolts are used to secure the laps.
But the lap-and-butt form is also used in doors and in other cabinet work. It is of great service in paneling.
A rabbet is formed to receive the edge of the panel, and a molding is then secured to the other side on the panel, to hold the latter in place.
Scarfing.—This method of securing members together is the most rigid, and when properly performed makes the joint the strongest part of the timber. Each member (A, Fig. 212) has a step diagonally cut (B), the two steps being on different planes, so they form a hook joint, as at C, and as each point or terminal has a blunt end, the members are so constructed as to withstand a longitudinal strain in either direction. The overlapping plates (D) and the bolts (E) hold the joint rigidly.