projected open, and as at this stage the clear opening will he shown, commence the door by projecting the top and bottom edges from the inner angle of the opening. Eventually the lower line will disappear, being hidden by the back face, but it is necessary to first draw it to obtain the size of the door and the thickness.
Set off along the top line, the width as shown in the opening, and draw in the rebate, projecting the back edge I in. beyond the rebate line just obtained. Go back to point A and set off the thickness, when the inner face may be completed. The filling in of the minor details should offer no difficulty. The position of the shelf is located upon the dotted line representing the inner edge of the case as at a, projecting back the thickness of the door to find the plane of the edge of the shelf.
An enlarged detail of the joint between the end and top of the case is shown in Fig. 2. The bottom rail is stub tenoned into the ends and the shelf is housed in fg in.
The Quoin of a 14 in. Brick Wall in single Flemish Bond is shown on page gi, with three courses of footings resting on the surface of the concrete foundations. The drawing further illustrates the technical terms, " toothing," " racking back " and " carrying up the quoin " ; the first being the method of connecting to a cross wall, the second the method of suspending the work in successive set-backs right across the thickness, for the purpose of bonding the continuation of the wall. Some difference of opinion exists among bricklayers as to the best way to lay the bricks, frog up or down, but undoubtedly in all ordinary cases it is better workmanship to lay wit lit he frog upwards, as, placed thus, it is sure to get filled with mortar. The bottom course must in all cases have the frogs uppermost, and the top course the frogs downwards.
Carrying up the quoin is the building up to the two ends of a wall in advance of the remainder for the purpose of lining the courses to keep them level. Quoin is the corner or
94 PROJECTING A GANTRY
salient angle of a wall, also any partic ular stone or brick composing it.
The Builder's Gantry page; 93w!is a structure used in large towns, where there is much tralfic, for the purpose of carrying the scaffolding, used in erecting the walls of buildings, well above the heads of pedestrians, the scaffold proper starting from the platform shown in the drawing, Which is raised some 10 or 12 ft. above the pavement. It is composed of stout timbers from 7 in. square to it in. square, according to the spacing and load to be carried, secured together with timber dogs. In some few instances where the job is expected to last some years, the standards or uprights are framed and tenoned into the heads and sills. The platform is composed of deals such as are used for floor joists, and they are lightly spiked to the heads. A light sloping guard or " fan " is run around the front and ends to prevent maierial tailing into the street.
To draw the gantry, commence by projecting the rectangle, a- b c-d, shown in dotted lines, at an angle of 30 wit h the horizontal to the left, and another rectangle level with the floor, towards the right ; these two rectangles, placed isometrically, will contain the main structure, and the various dimensions can be scaled off upon the root lines. The chief dimensions are: height, pavement to floor, 11 ft.; width out to out of standanls, 9 ft.; distance between standards in front, 9 ft. ; space between joists, 1 ft. 3 in.; height of handrail, 3 ft.; height of braces, 6 ft. 6 in.
The Draper s Counter shown on page 95, also orilio-graphically on page 70, will test the student's carefulness, and if he does not work accurately to previous instruc tions as to measuring off the details upon the root lines and projecting them into the picture where required, he need not hope to succeed in producing a correct isometric projection. Portions of the top and the front framing are supposed to be cut away so that the interior construction can be seen. It is perhaps scarcely necessary to say that the counter will not be so made, and the parts shown removed will be continued,
96 A DRAPER'S COUNTER
as indicated by the dotted lines. The front of this counter is made of 11 yellow deal; each section is framed in one piece with stiles at the ends rarming to the floor, the intermediate mountings stub tenoning into the rails. The bottom rail finishes about 3 in. below the plinth, which is fixed to blocks or " backings " nailed upon the divisions. The plinth or skirting runs across the door in the return end, and is cut at a bevel in the joints, as shown in Fig. 7, page 70, to pass clear. The top has a considerable overhang in front anil is thickened outside with a moulded lining screwed on ; it is secured by slipping-buttons fitting into grooves in the tilting pieces and screwed underneath ; this is to prevent splitting, which such a wide board would be liable to do if fixed immovably.
The carcase is constructed by forming tenons upon the top ends of the divisions in a notch cut to receive the back rail, and at the lower end they are housed or grooved to receive the f in. bottom, which is secured by gluing angle blocks beneath, the intermediate rails forming divisions for the drawers, double tenoned into the divisions at each end, and the runners are single tenoned into them for | in., also housed --¡\ in. into the uprights. As a rule, dust boards are not provided in these counters ; if they were required they would be inserted in grooves similar to those in the til'ing pieces.
To draw this example start at A-A, which represents the salient angle of the front framing or mitre marked M in Fig. 1, page 70. Set off on this the height to the under side of the top, and project the dotted lines to left and right, forming the root lines, and, working from the plan on page 70. space out the dimensions of the divisions, thickness of the front, etc. It would be both wearisome to read and probably useless to give instructions for placing every detail in the picture, as words would give no clearer description than the drawing itself.
Circles and Curves—When a circle is projected isometrically it becomes an ellipse, or, to state the facts with
98 CIRCI.ES IN ISOMETRIC
more exactness of expression, an ellipse in an isometric projection represents a circle in either plan or elevation, and, from the association of ideas consequent upon the observation of natural phenomena, the mind invariably assumes that a circle is represented when the ellipse is rendered isoinetrieally. Therefore it follows that if we desire to suggest an elliptic solid isometrically the only way in which we can differentiate it from a cylinder is to label it.
The readiest method of rendering the circle isometrically is, as advised for projecting polygons, to enclose it within a square, and to draw projectors from various points in the curve to the sides of the square, then to redraw the square in the form of a rhombus, by projecting its sides at an angle of 30° with the horizontal, thereafter transferring the projected points from the sides of the square to the correspond ing sides of the rhombus, and then drawing from these ¡joints lines parallel with the root lines, locating the points in the curve upon them from the original drawing and tracing the elliptic curve through these. The method is shown on page 97. Fig. 1 is the circle to be shown isometrically. Proceed to enclose it within the square a-l-c- d, whose sides are made to touch the circle. Draw the diagonals a--c. and b-d, also the transverse diameters 1-3 and 2-4. These lines will locate eight points in the curve; if more are required, any number of intermediate points may be plotted by projectors perpendicular to the sides as shown at 0, x, y. Fig. 2 shows the square in isometric projection when it becomes a rhombus. The various perpendiculars are transferred from Fig. 1 to Fig. 2, where they are similarly numbered and their lengths marked—i.e. the distance from the adjacent side of the square that the original curve passes through them— and the curve can then be drawn through these points. Fig. 3 shows the method of placing the circle in the vertical plane. If this is projected in the usual manner from the T square held horizontal, the set square; of 6o° should be used to project the sides of the containing square a- b-c -d, and the diagonal b- d becomes the major axis of the ellipse. If
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