The Technique of FURNITURE MAKING

Entasis

Tapered shafts or columns with straight sides give the optical illusion of curving inwards, therefore classical architecture gave a slight outward swelling (entasis) to counteract the tendency, and to convey an impression of the weight-bearing function of the column. Various methods are used of which 349 gives one of the simplest and most satisfactory, for the curve must be subtle or the effect becomes exaggerated. The height of the column AB is first drawn, also the top EF and bottom diameters CD. Semicircles with centres A and

349 Entasis

radii AC and BE are then drawn, and perpendiculars erected from the smaller semicircle to cut the larger semicircle at 3. The arc C3 is then divided and from points 1, 2 perpendiculars are erected to cut corresponding divisions in the height of the column, yielding points through which the curve CE can be drawn.

Arches

Various forms of arch are shown in 350:1 together with the geometric construction. The points from which the curve of the arch springs are known as the springing-line, the exterior curve the extrados and the interior curve the intrados.

Tracery

Gothic tracery used as infilling or 'foliation' in window arches, etc., and still called for in traditional church-work, is based on geometric principle, and 350:2 gives various examples with their constructions. Where there is a demand for this type of work, local church examples should be examined.

Repeat patterns

Practically all decorative patterns, whether carved, moulded, inlaid or applied, have a geometric basis, and are in essence composed of curved or straight lines repeated in regular sequence. Even representations of fruit, flowers, shells, etc. are stylized to fit within circles, squares and diamonds, etc. Once the principle has been established it is relatively simple to break down the pattern into its component parts, and thus establish the structure on which it is built up.