This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
In all which has preceded, the drawing has been laid out along the lines of the axes. But besides these are some conventional methods by which the drawing of profiles in section or in elevation can be facilitated. Let us take for example a fragment of the Doric order - one from the Parthenon, Fig. 9. To reproduce this drawing one should measure the different projections by referring them to one single vertical line. In this case the axis of the column would not furnish a convenient axis for measurement, as with exception of the column, it determines nothing. It is best to proceed just as in measuring an existing order, that is, by dropping a plumb line from the overhanging cornice and measuring the distance from that plumb line to the various members. But this vertical line from the outer member of the cornice will be only useful for laying out the profile and in locating the axis of the column; axes should be drawn in every other possible case. For instance, place the column on the axis A; the triglyphs, on B; the metopes, on C; the head of the lion, on D, etc. To obtain the heights draw the principal divisions in first; the total height of the capital, the total height of the architrave, the complete frieze, the complete cornice; then draw in each detail in height within these first divisions.
The channels of the triglyphs, the guttae, etc., are all drawn in on their own axes. As for the channels of the column, these can only be drawn by projecting them. Do not copy them from the drawing, but draw out a plan, dividing the circumference into twenty parts or whatever number the design calls for, and project these divisions up to the elevation.
Study the model carefully before copying it; thus, in this example a close examination will show that the architrave is slightly sloping while the frieze is not. If the student has the opportunity to see mouldings similar to those which he is drawing, he should study them carefully. It cannot be too often repeated that architectural drawing should not confine itself to exercise for the hand; there should be the opportunity for real study of whatever is drawn.
Limiting Lines. In geometry, we have learned what the abscissa and the ordinate are; i.e., the elements of reference by which a point is referred to a system of fixed rectilinear co-ordinate axes. For every part of a design of which the elements are not geometrical lines, such as a right line or circle, the method of abscissa and ordinate is used, as in laying out profiles of mouldings or curved ornaments such as eggs in the egg and dart motive. Take for example a baluster, Fig. 10; it is evident that it should be drawn in relation to its axis. The student will mark the general divisions, A B the die, B C the base, C D the shaft, D E the capital, after which the secondary lines of the mouldings should be drawn in. Between C and D, however, the profile of the shaft may vary very much and the student will not be able to copy it except by laying off horizontal divisions. For that purpose, draw the limiting lines of its greatest width mm, mark its point of application M, and repeat this operation on the drawing. In the same manner lay off the line n n, and the point N, which gives the smallest diameter of the shaft, and do not mark these points by a single point with the pencil, but be careful to draw the limiting (in this case vertical) lines at every point, and do not erase them until after you have inked in the drawing. These lines will be a safe guide and will enable one to make an exact and clean drawing.
Fig. 9. Capital and Entablature from the Parthenon.
As another example take the fragment of the cornice with different ornaments, taken from the Temple of Concord, at Rome, Fig. 11. The construction lines marked on the drawing, and which should be kept in pencil until the drawing is completed, show especially well the method previously explained.
Finally, to produce an architectural drawing with precision demands primarily a rational method and methodical habits. The design gains by its facility, but the method can only be a general one In its application, an intelligent draftsman will recognize each time what should be the logical sequence in carrying out the drawing. And still, all of this will be only the mechanism of the design; it is necessary to put into it taste and sentiment. For all of this there is only one precept - it is by practice that one becomes a good workman. Oblique Projections. It happens often that in an elevation or section architectural motives are represented obliquely in relation to the principal plane of projection. Thus in a circular building a series of similar windows are in elevation at different angles, consequently the widths differ, but the heights do not.
Fig. 10. Baluster.
It is necessary to become familiar with these conditions of drawing which occur frequently. It is here above all that geometry will be very useful, for that study includes the planes of projection and planes of development.
While there is some little difficulty, there is also much profit to be gained in projecting an architectural motive at an angle. In order to project a motive at an angle correctly, one must understand the motive thoroughly. An architectural arrangement drawn out in direct elevation only, will not tell the whole story, but if drawn in oblique projection a thorough understanding of the arrangement is gained.
Fig. 11. Entablature from the Temple of Concord, Rome.
It is recommended, therefore, as a very useful exercise to draw out in oblique projections, designs that are made in direct elevation; it is a good exercise in design, but above all it is an excellent preparation for architecture, compelling the designer to analyze his model and to see it as a whole; to understand its projections and to comprehend the position of the different details. The designer realizes that he is working on the real building rather than in simple imagination, and so will soon see of how much advantage these exercises will be to him.