Where two mouldings of unequal width intersect on one plane then the junction is a bevelled mitre as distinct from a true mitre of 45° (see Mitre, scribed and scarf joints, Chapter 20); but where two mouldings of equal width intersect then the mitre lines on each must be the same length, therefore the angles must be equal, or, as commonly stated, the mitre must halve the overall angle. Figure 351:4 shows the correct mitre line of two pieces of equal width meeting at an angle, and the dotted lines the effect of unequal angled cuts, where the cut (A) is longer than the cut in the opposite member. This halving of the overall angle is not possible in raking moulds in cornices, pediments, etc. as the side or return mould must have a right-


352 Proportional reduction and enlargement (2)

angled cut, and the raking or face mould an inclined cut vertical to the side of the carcass or door framing, as shown in the dotted line at A (352:4).

It is necessary, therefore, to alter the section of either the side mould or the raking mould so that they correspond, and 352:5 shows the method. As the raking mould is normally to a fixed section this is drawn in first and the profile added as A. Lines are then drawn through salient points parallel with the slope, and from the points of intersection other lines at right angles to the slope. From point X draw a true horizontal XZ equal in length to XY which is the thickness of the face mould, and on the centre X describe arcs as shown, dropping verticals from XZ to meet the lines drawn parallel to the rake. The points of intersection will then enable the profile of the return mould to be drawn in B. To ascertain the profile of the top return mould (C) it is only necessary to transfer XY with its plotted points to the horizontal plane and drop verticals to give points of intersection as with B. If the raking mould is curved (352:6), the arbitrary lines through the salient points of the profile A must be drawn at right angles to the bed of the mould, and should not follow the axis of the sweep.

Curved mouldings

The junction of a curved and straight moulding, or of two curved mouldings of dissimilar sweep or direction, is not in a straight line, therefore either the profile of one must be altered or the mitre line itself must be curved. Obviously the latter method is always simpler and the drawing below shows the procedure. Arbitrary lines are drawn either from the salient points of the profile 353A or, if the moulding is composed of one large member only, at any convenient spacings, and the curve is then drawn through the points of intersection.

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