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the head, as at B, Fig. 4. The stiles of the top lights are grooved for the glass, not rebated. The dotted lines in Fig. 8 indicate position of trusses, the outer four being king post trusses.

Circle-011-Circ.Ie Entrance Doors and Frame.—This» is an example of projection that will require careful and painstaking work on the part of the student if he is to succeed. The author is not aware that this particular form of circle- 011-circle work has hitherto been dealt with in books, though doubtless now it will become common enough. It is perhaps also the reason that arcliitccts rarely design door frames in this manner, as it is difficult to get the work properly done. This is not the place to enter into the practical details of construction, the remarks here being comined to the methods of producing the drawings and obtaining the moulds. There is a full description in " Modern Practical Joinery " of how these frames are to be constructed when based upon the solid known as tliecuneoid, and generally those instructions would apply equally to the frame, etc., now to be described. The head of this frame, also of the soffit lining and the architrave, is based upon the cone, as indicated in the small sketch, Fig. 7—that is, the edge of the frame and face of the lining radiate equally at the crown and springings.

The plan should be first drawn ; and should not present much difficulty at this stage ; a centre line should be drawn and produced info the elevation, and the centre of the plan curves located upon it, by producing the splayed reveals until they intersect at A . This forms the apex of a cone (or, to be exact, a semi-cone), in which the surface of the parts composing the head lie, and becomes the common ccntre for describing the various curves in the plan. Having iinished the plan so far as the members of the frame, etc., are concerned, the elevation may be projected therefrom.

The opening in the wall should first be drawn, and it should be noted that, although the head is shown as a semicircle on the flat, it is not so actually, the true contour being

78 PROJECTING CURVED SECTIONS

elliptic. What is actually drawn in the elevation is a projection upon a plane standing on the line B-B. The dotted projectors indicate where the various lines in the elevation are obtained from in the plan, and no difficulty should be experienced in tracing these; and we can now proceed with the sectional elevation. Fig. 3, which is the really difficult part of this example.

To obtain the Vertical Section Draw the ground line, mark point C', and project it to the head. This point represents the highest point of the reveal in the brickwork, as indicated by the dotted projector c'-c"; intersect this by a horizontal projector from the crown of the arch / as shown. Next consider that the section we are drawing is a view obtained by looking in the direction of the arrow on Fig. 1, at a plane passing through the line C-/1'; if then we draw projectors perpendicular to C-A' from the various members and transfer these to the ground line in Fig. 4, as points 1', 2', 3', 4', 5', etc., the location of the various edges will be obtained for projecting into elevation up to the springing line, where the curves commence ; and we next have to plot points in these. Let us take the sight line of the opening as a starting point. Divide the elevation of this line into as mrny parts as convenient, as at a, h, e, d. /. Draw horizontal projectors from these points across the section, also drop projectors from them into the plan, cutting the line of the arch therein in points a', 6', e', d', /', project the intersection points to C-A' as shown by the chain lines ; then transfer them to the ground line in Fig. 3, as at a'", V", e"\ etc., and raise perpendiculars to intersect the horizontals from the original points a, b, e, etc. These intersections give the points a", U1, e2, d2, through which to draw the curved edge of the arch soffit in sectional elevation. They will be easily followed by inspecting the drawing. The arrises of the frame, the lining and the architrave are obtained in like manner, by producing the projectors in the plan, to cut the desired line, then projecting these points to the line of section and transferring them to Fig. 4, where they are to be inter-

Circle-on-Circle Entre

Circle-on-Circle Entre

Fig. I. Plans. Fig. 2. Outside Elevation. Fig. 3. Inside Elevation. Fig. 6. Method of obtaining Face Mould. Fig. 7 Constructional l)iagr

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