Kitabı oku: «Handwork in Wood», sayfa 10

Fig. 289. The Way a Mitered Joint Opens on Account of Shrinkage.

In window sashes, the dovetail joint, Fig. 267, No. 47, is the common one at the upper end of the lower sash and the lower end of the upper sash, and the mortise-and-tenon joint modified is used at the lower end of the lower and upper end of the upper sash. The glass takes the place of the panel. In blind sashes, the pinned mortise-and-tenon joint, Fig. 267, No. 38, is commonly used.

When panels are joined together to enclose a space, then we have what is properly called cabinet construction. Illustrations are cabinets, bureaus, desks, lockers, chests, etc.

In all these cases, the constructed panels may be treated as separate boards and joined together with dowel pins or splines or dadoed together without any other framework, tho the corners are often reinforced by cleats or blocks glued into them. Sometimes, however, as in chests, Fig. 290, posts are used instead of stiles, and rails are mortised or doweled into them and the panels set into grooves in both posts and rails. In this case the bottom is raised from the floor, and may be dadoed into the bottom rails, or dowelled into them or even supported by strips attached along their lower inside edges. The chest really is a union of both paneled and framed structures.

Fig. 290. Chest Construction.

(4) FRAMED STRUCTURES

The principle of the framed structure is similar to that of the panel construction in that the object is to allow for shrinkage without harm to construction and also to economize materials. Common examples are tables, chairs, work-benches, and frame houses.

The Making of a Table. The standard height of a table is 30". There should be 25" clearance under the rails. This leaves approximately 4" for the width of the rails. Assuming that the table is to be of a simple straight line type with one drawer, the following method of procedure is suggested:

Cut the boards for the top to the approximate length and stick, (see p. 48) and clamp them, so as to season them as well as possible before jointing.

Dress to size the legs and rails. Stand the legs in their proper positions relative to each other, and mark them F R (front right), F L (front left), B R (back right), and B L (back left). Plow out the grooves on the inside of the rails for the fastenings of the top, Fig. 297, D, if they are to be used. Lay out and cut the tenons and mortises for the end rails and back rail.

The proper form of the tenon is one with a wide shoulder above it so that the top of the leg above the mortise will not shear out. The rails should be set near the outside of the leg so that the tenon may be as long as possible and the portion of the leg inside it as strong as possible. A haunched mortise-and-tenon joint, Fig. 267, No. 43 is sometimes used, giving additional lateral stiffness to the rail. The proper proportions are shown in Fig. 291. When cut, these parts should be temporarily assembled to see if they fit.

Fig. 291. A. Cross-Section Thru Back Left Leg and Adjoining Rails of Table. (Plan).

B. Elevation, Showing Wide Shoulder on Tenon of Rail.

Inasmuch as a drawer takes the place of a front rail, the front legs must be tied together in some other way. For this purpose two stringers or drawer rails may be used, their front edges being as far from the face of the legs as are the rails from the side and back. The upper drawer rail may be dovetailed at both ends into the tops of the legs, as shown in Fig. 292. If this takes more room than can well be spared from the depth of the drawer, it may be omitted, but it adds greatly to the stiffness of the table and is an excellent means of fastening on the top by the use of screws passing thru it.

Fig. 292. Table Construction: Upper Drawer Rail of Table Dovetailed into Left Front Leg.

The drawer rail, also called the fore edge, is long enough to partly overlap the side rails, into the lower edges of which it is gained so as to be flush with them, and may be fastened to them with screws, Fig. 293. The construction may be further strengthened by also doweling the end of this stretcher into the legs. If there are two drawers, the partition between them may be doweled or gained into these upper and lower stretchers.

Fig. 293. The Fixing of a Drawer Rail, Seen From Below.

If the legs are to be tapered or otherwise shaped, that should be done next. Then glue and assemble the end rails with their proper legs, taking care to see not only that the joints come up square, but that the legs are in the same plane. Finally assemble the whole, inserting, if necessary, a temporary diagonal brace to insure squareness, Fig. 294. When dry, clean up the joints. For the making of a table drawer, see above, p. 191.

Fig. 294. Brace to Insure Right Angles in Assembling a Framed structure.

To fit the drawer to its place, runners and guides, Fig. 295, must first be fastened in. The runners are in line with the drawer rail, and are glued and nailed or screwed to the side rails between the back of the lower stringer and the back posts. On top of them and in line with the inner face of the legs are the guides running between the front and back posts. Or the runner and guide may be made of one piece properly rabbeted out.

Fig. 295. Drawer Mechanism.

If there are two drawers, a double runner lies between, and is gained into the middles of the back rail and the stringer, and on it is a guide for both drawers, equal in width to the partition between the drawers. The drawers should run easily in their proper places. In order to insure this, the drawer should be slightly narrower than the opening which receives it. A little French chalk, rubbed on the sides and runners, makes the running smoother. Sometimes the opening for a drawer is cut out of the front rail, as in Fig. 296. In this case the drawer runners are supported between the front and back rails, into which they may be gained.

Fig. 296. Opening for Drawer Cut Out of Front Rail of Table.

For the making of the table top see edge-to-edge joint, p. 172. Dress up the top to size, taking special pains with the upper surface. If the grain is crossed, use the veneer-scraper, Fig. 151, p. 92, then sand, first with No. 1, then with No. 00 sandpaper, finish the edges carefully, and attach to the frame.

For fastening the top to the table rails, several methods are used. The top may be screwed to the rails by the screws passing thru the rails themselves either straight up, Fig. 297, A, or diagonally from the inside, B, or thru blocks or angle irons, C, which are screwed to the inside of the rails, or thru buttons, or panel irons, D, which are free to move in a groove cut near the top of the rail. The last method is the best because it allows for the inevitable shrinkage and swelling of the top.

Fig. 297. Methods of attaching Table Top to Rails.

Chairs may be so simplified in form as to be possible for the amateur to construct. The two front legs and the rail and stretcher between them offer little difficulty because the angles are square.

The two back legs, may, for the purpose of simplification, be kept parallel to each other and at right angles to the seat rails between them, as in Fig. 298, A, and not at an angle as in B. The joining of the back will then offer little difficulty. The principal difficulties lie in the facts that for comfort and appearance the back of the chair should incline backward both above and below the seat, and that the back of the seat should be narrower than the front. By keeping at right angles to the floor the part of the back legs which receives the seat rail, the side seat rails will meet the back legs at a right angle in a side view, Fig. 298. The back legs should be slightly shorter than the front legs, as shown in D.

Fig. 298. Chair Construction.

The second difficulty involves the making of inclined mortise-and-tenon joints, A, where the side rails fit into the legs. The making of these can be facilitated by laying out a plan of the full size and taking the desired angles directly from that. It is common to reinforce these joints with corner blocks glued and screwed in place as shown in A. If there are additional rails below the seat rails, the easiest way to fit them in place is first to fit and clamp together the chair with the seat rails only, taking pains to have all angles perfectly true, and then to take the exact measurements for the lower rails directly from the chair. The same method may be used for laying out a stringer between the lower rails.

If it is desired to bow the rails of the back, which are above the seat rail, this can be done by boiling them in water for 30 minutes and then clamping them over a form of the proper shape, with a piece of stiff sheet iron on the outside, as in Fig. 299. They should be thoroly dried in a warm place. Then the tenons may be laid out on the ends parallel to a straight-edge laid along the concave side. The chair bottom may be made of solid wood, either flat or modeled into a "saddle seat;" it may be covered with cane or rush, or it may be upholstered.

Fig. 299. Bending Boards into Shape after Boiling Them.

To upholster a chair seat, a frame should first be made of the shape shown in Fig. 298, C. The strips are about 2" wide and ½" thick with their ends half-lapped. The seat rails are rabbeted ½" deep and ½" wide to receive this frame, which should be ⅛" smaller all around than the place to receive it. The returns at the corners fit around the legs at ⅛" distance from them. This ⅛" provides space for the coverings. After the frame is fitted, it is covered with 3" webbing tacked firmly to the upper side. The webbing which goes back and forth is interwoven with that which goes from right to left. Over this is stretched and tacked (also to the upper side) a piece of unbleached muslin. A second piece of muslin is tacked to the back edge and part way along the side edges, leaving for the time the corners unfinished. In the pocket thus formed horsehair or other stuffing is pushed, care being taken to distribute it evenly and not too thick. When the pocket is filled, the muslin is tacked farther along the sides and more hair put in, until the front is reached, when the muslin is tacked to the front edge. The corners are now drawn in tight, a careful snip with the scissors parting them diagonally so as to lie in well. The partings may be turned down and tacked on the under side of the frame.

Finally the leather or other covering is stretched over the whole as evenly as possible. The corners should be left to the last, then clipped diagonally to the exact inside corner and the partings drawn down and tacked, as was the muslin. The superfluous leather may then be trimmed off, and the seat should fit in its place. Or the seat frame may be omitted, and the coverings tacked directly to the chair rails.

Fig. 300. House Construction.

The balloon-frame house is a typical form of framed construction, Fig. 300. The essential parts of a balloon-frame are:

1. SILL, 4" × 8", which rests on the foundation.

2. BEAMS, 4" × 8", which rest on the cellar posts, 6"×6". (Not shown in illustration.)

3. FLOOR JOISTS, 2" × 8", which rest on the sill and beams.

4. CORNER POSTS, 4" × 6", with 2"×4" studs nailed to them.

5. STUDDING, 2" × 4", which stand 16" between centers.

6. WALL RIBBON, or girt, 1" × 8", which supports the upper story joists.

7. PLATES, two 2" × 4" nailed together, resting on studs.

8. RAFTERS, 2" × 6", which support the roof.

9. TIE-BEAMS, 2" × 6", which prevent the roof from spreading the walls. (Not shown in illustration.)

10. RIDGE-POLE, 2" × 8", against which the rafters butt.

11. BRIDGING, 2" × 2", which stiffens the floor joists.

12. SHEATHING, (1" thick), put on diagonally to brace the building. The rest is covering.

13. FLOORING, (See also Fig. 301.)

In flooring, Fig. 301, the boards are made narrow so as to reduce the size of openings at the joints when they shrink, and also to reduce the tendency to warp. They may be laid side by side as in the cheapest floors, or matched to close the joint. For difference between slash- and comb-grain flooring, see Fig. 55, p. 42.

14. BUILDING PAPER.

15. SIDING OR CLAPBOARDS, (See Fig. 301.) may either overlap without a joint or be rabbeted to fit. The best siding is rabbeted.

16. WATER-TABLE.

17. CORNER-BOARD.

18. FURRING.

19. SHINGLES.

20. LATHING.

21. CEILING, Fig. 301, consists of matched boards having a "bead" to disguise the joint and give a decorative effect.

Fig. 301. Siding, Ceiling, Flooring.

TYPES OF WOODEN STRUCTURES

References¹⁹

Simple Joined Structures.

Benson, pp. 32-37.

Goss, pp. 91-96.

Noyes, School Arts Book, 6: 89, 179.

Wheeler, pp. 86, 219-227, 376.

Sickels, p. 120.

Griffith, pp. 84-104.

Panel and Cabinet Construction.

Goss, pp. 117-118, 148-151.

Compton, pp. 146-151.

Sickels, p. 134.

Wheeler, pp. 366-372.

Framed Structures.

Crawshaw.

Wheeler, pp. 203-206, 238-297.

Sickels, p. 124.

Building Trades Pocketbook, pp. 221, 230.

Coverings.

Sickels, pp. 128-131.

Goss, pp. 141-144.

Chapter IX.
PRINCIPLES OF JOINERY.²⁰

1. Avoid multiplication of errors by making all measurements (as far as possible) from a common starting point, and laying off all angles from the same line or surface. Illustrations of this principle are as follows: Before proceeding with other processes, a working face and working edge and as many other surfaces as will finally appear in the finished piece, should be trued up. At least the working face and working edge are essential to the proper "lay-out" of the piece, whenever measurements are made from an edge.

In laying out a series of measurements, it is important, when possible, that the rule be laid down once for all, and the additions be made on that, rather than that the rule should be moved along for each new member of the series.

In scoring around a board with knife and try-square, the head of the try-square should be held against the working face in scoring both edges, and against the working edge in scoring both faces, and not passed from one surface to another in succession.

In the laying out of a halved joint, Fig. 265, Nos. 15-19, p. 178, the gaging is all done from what will be one of the flush surfaces of the joined pieces. Then, if the gaged line should be slightly more or less than half the thickness of the pieces the closeness of the joint would not be affected.

2. When possible, in laying out a joint, use the method of superposition. Fig. 302. By this is meant the method by which the lay-out of one member is obtained directly from the other by laying (superposing) the latter on the former and marking or scribing the needed dimensions directly, instead of by measurement. It has the advantages of simplicity, speed, and greater probability of fit.

Fig. 302. Marking by Superposition.

Familiar illustrations are in the making of halved joints, Fig. 265, Nos. 15-19, p. 178, dovetail joints, Fig. 267, Nos. 42-45. p. 180, and scarfed or spliced joints, Fig. 264, Nos. 4-7. p. 177.

3. Work systematically. In case the same process is to be repeated on a number of parts, complete this process in all before taking up another process. This is the principle of the division of labor applied to the individual workman.

In laying out duplicate or multiple parts, the proper cross measurements should be carefully laid out on one piece and then transferred with a try-square to the other parts laid accurately beside it. So when a number of like pieces are to be gaged, all the parts requiring the same setting should be gaged before the gage is reset for another gaging. This is a great saving of time and insures accuracy.

In making a number of like parts, if they are not too large much of the work can often be done in one piece before it is cut up. For example, to make a number of slats from a given piece of wood, the piece may first be brought to such dimensions that the length will be correct for the finished pieces and the thickness of the piece be equal to the width of the slats, Fig. 303. The face may then be gaged with a series of lines so that every other space will be equal to the required thickness of each slat, and the alternate spaces be just sufficient for the saw kerf and dressing. The slats may then be ripped apart and dressed to size.

Fig. 303. Making a Number of Like Pieces from a Given Piece.

Or a long strip may be planed to thickness and width and then be sawn up and finished to the proper lengths. For example, in a mitered picture-frame it may be convenient to plane up two pieces, each one long enough to make one long side and one short side.

In fitting up framed structures each part when fitted should be distinctly marked, so that there may be no confusion in assembling.

4. Where practicable secure the same conditions of grain in different elements of joined structures.

Illustrations of this are as follows: The grain of the sides of a box should run continuously around the box, or, in the case of a tall, slim box, the grain of all the sides should run up and down. In either case, the grain in the different sides is parallel. In a rubbed joint, Fig. 269, No. 70, p. 182, to be planed down afterward, in case the grain is not straight, much trouble in planing may be saved if the different pieces are laid so that they can all be planed smooth in the same direction. This may not be possible where the boards are joined so as to match the grain, as in quartered oak, or where the annual rings of slash boards are made to alternate in direction so as to lessen warping, Fig. 280, p. 186.

5. Where possible, allow for shrinkage without prejudice to construction.

The most obvious illustration of this principle is panel construction. In a panel, the frame, which is comparatively narrow, follows the principal dimensions, and hence does not seriously shrink or swell itself. But the panel, which is grooved into the frame can shrink or swell without harm to the general structure.

In a gained joint, as in a case of shelves, Fig. 266, No. 29, p. 179, the gain in the uprights does not extend quite to the front of the shelves, and there is a corresponding slight shoulder at the front end of the shelf, so that if the shelf and support shrink unevenly, no gap will be apparent.

A drawing-board, Fig. 280, p. 186, is so made that it can shrink or swell without losing its flatness. Shingles when properly laid, can shrink or swell without the roof leaking.

6. Where feasible, undercut joined surfaces so as to give clearance on the inside and insure a tight appearance. But glued surfaces should be made to meet flat.

Illustrations of this principle are as follows: The inner end of the socket in a dovetail joint, Fig. 267, No. 48, p. 180, may be undercut slightly so as to insure the pin's falling close into place.

The shoulder of any tenon may be undercut so as to allow the edges of the tenoned piece to close up tight against the mortised piece.

In an end-lap halved joint, Fig. 265, No. 17, p. 178, the edges should meet all around; if they are to be glued together, they should not be undercut or they will not glue well.

In matched flooring, the underside of the boards is slightly narrower than the upper side so that the joint may close on the upper side without fail, Fig. 301, p. 201. The ends of flooring boards are also slightly beveled so as to make a tight fit on the upper side.

7. Select the simplest form of joint and use the smallest number of abutments (bearing surfaces) possible, because the more complicated the joint or the greater the number of bearing surfaces, the less likelihood there is of a sound and inexpensive construction.

Illustrations of this principle are as follows: Usually a single mortise-and-tenon joint is better than a double one because of simplicity, strength and ease of making. Where much surface is required for gluing, a double one may be better.

In a dovetail dado, Fig. 266, No. 28, p. 179, it is usually sufficient to make the dovetail on one side only.

Many very elaborately spliced joints have been devised, which have no practical advantage over the simple ones, Fig. 264, Nos. 4-7, p. 177.

A butt joint, Fig. 264, No. 11, is stronger than a mitered joint, Fig. 268, No. 52, in a box, for the latter is almost sure to shrink apart. Where appearance is important, a ledge and miter joint has the advantage of both, Fig. 268, No. 58.

8. Keep a due proportion of strength between the fastenings (joints) and the pieces fastened: i. e., the construction should neither be frail on the one hand, because the pieces of wood are weakened by too much cutting, nor clumsy, on the other hand, because then the fastenings would be inordinately strong. In other words, the different parts should be equally strong.

Illustrations of this principle are as follows: In a fished joint, Fig. 264, No. 2, the plate should be attached so as to reinforce the splice at the weakest point.

In a scarf joint, Fig. 264, Nos. 5 and 7, the angle should be oblique enough to give the greatest leverage.

In a tusk tenon, Fig. 267, No. 40, the tenon is made but one-sixth the thickness of the timber, whereas the tusk is made much larger.

Where a mortise is to be cut in a timber bearing weight, it should be cut in the neutral axis, where the cutting of fibres will weaken it least.

In the mortise-and-tenon of a table-rail, Fig. 267, No. 43, there should be a wide shoulder above the tenon of the rail so that the top of the leg above the mortise will not shear out. The mortise should be as near the outside of the leg as possible so that the inner corner of the leg may remain strong. The tenon should be strong enough to share the strain with the shoulders.

A dado joint, Fig. 266, No. 25, should not be so deep as to weaken the supporting board.

A tenon should not be so large as to weaken the mortised piece.

Pins or other fastenings, Fig. 267, Nos. 38 and 39, may weaken rather than strengthen a joint if they are so placed or are so large as to shear or crush their way thru the timber.

9. Place each abutting surface in a joint as nearly as possible perpendicular to the pressure which it has to transmit.

Illustrations of this principle are as follows: the angle in a strut joint, Fig. 266, No. 62, should be equally divided between the two beams.

The thrust joint, Fig. 268, No. 63, in a bridge truss, is exactly at right angles to the pressure.

It is on account of this principle that a spliced joint for compression, Fig. 264, No. 4, is different from a spliced joint for tension, No. 5; and that a housed braced joint, Fig. 269, No. 66, is better than a plain braced joint, No. 65.

A joint to resist vertical cross strain is stronger when scarfed vertically than horizontally.

THE PRINCIPLES OF JOINERY

References²¹

Goss, p. 132.

Adams, p. 12.

Rivington, Vol. I, p. 57.