This section is from the book "Modern Buildings, Their Planning, Construction And Equipment Vol1", by G. A. T. Middleton. Also available from Amazon: Modern Buildings.
(Contributed by W. Hooker)
The Science of Masonry and Stone-Cutting will be treated at length in another Volume of this work, but it is thought advisable to introduce here a few remarks of an elementary character, in order to render this Volume complete in itself.
The first step of the mason's foreman on receiving the Designs for the work is to calculate, by means of fully detailed drawings, the shapes and sizes of the various stones, with their measurements, for transmission to the quarry. This is effected by means of rules, set-squares, scales, compasses, etc., as detailed out in the following paragraphs. A list of the more common tools and levels, etc. will be also found in continuation.
The straight edge, usually of pear or other closegrained wood, is, as its name implies, of a perfectly straight face and of convenient length.
Set-squares of 45, 60 and 75 degrees are useful. Needless to say, the above should be carefully tested for accuracy.
Compasses, large and small; and also beam-compasses or pointers clamped to a hard-wood lath, and capable of being adjusted to any convenient length.
The usual scales, proportionals, and French curves, as well as a protractor, for setting: off angles.
Most masons make their own sweeps, generally of clean deal or other suitable wood planed down thin into strips and carefully trued up, nailed together with a tie of the same material as the angle, and fixed at the intersection of the crossings. The guide points are ascertained by calculation. The pencil or . steel scribe is held firmly in the angle formed by the crossings, and by a lateral movement (the sweep being kept hard against the pins) a curve of the desired shape is formed (see Fig. 216).
It is presumed that the rudiments of geometry are known. At the same time, a few solutions of useful problems may not be out of place.
To divide a line into any number of equal parts, as, for instance, to divide AB into six equal parts (see Fig. 217). Draw AC at any convenient angle with AB, and mark off six equal parts with the dividers as 1, 2, 3. 4. 5. 6. Draw BD, making angle Abd = Bac, and from B mark off equal parts as before. Join 6-A, 5-1, 4-2, 3-3, etc., cutting AB in 1', 2', 3', 4', 5'. AB is divided into six equal parts. There are other methods of solving this problem.
To divide a line CD proportionally to the divisions on a greater or less lineAB. Let AB be a greater line than CD, and let it be divided unequally in points 1, 2, 3, 4. Draw CD, and at C draw angle Dcf, making the line CF = AB. Mark off on CF the points 1, 2, 3, and 4 equal to 1, 2, 3, 4 on AB. Join FD, and from points 1, 2, 3, 4 draw lines parallel to FD, cutting CD in 1', 2', 3', 4'; CD will be proportionally divided to AB as required.
To set out a line in proportionate parts, i.e. diminishing in regular ratio. Let the line AB be required to be divided into twelve parts, diminishing towards the top. Take any convenient point C, and join AC, BC, making an angle of 35 or 40 degrees. Set off on a straight edge twelve equal parts, the total length being less than AB. Range this askew across the lines AC, BC until the extreme points o and 12 coincide with the lines, and prick off the divisions 1, 2, 3, 4, etc. as shown. Draw radiating lines from C through the points 1, 2, 3, 4, etc., and produced to AB. The points of contact 1, 2', 3', 4', etc. on line AB will mark the divisions required.
When any two converging lines are given whose point of junction is inaccessible, to draw a line that would bisect the angle which would be formed by the converging lines. Let AB and CD be the two converging lines. Take the point E on AB and draw any line EF, cutting CD in F. From F draw FG cutting AB in G, and making the angle Dfg = angle Bef. Bisect angle Efg by the line FH. Bisect FH in J, and draw KL at right angles to FH. KL if produced will bisect the angle formed by the converging lines.
The above are problems which are useful in setting out. The method of drawing arches, ellipses, and parts of conic sections, with their developments and projections, will be described in a subsequent Volume. Tools. - The tools of a mason are: Various sorts of chisels for dressing the stone, of different widths and sections, from the fine pointed chisel to the broad tool for droving- or finishing, generally ranging from 1/4 inch in width up to 3 or 4 inches; mason's picks for scappling; spalling hammers for rough dressing; wedges of iron or steel; feathers or slips of iron of a concave section; lewises and other devices for lifting and handling the stone; dividers for gauging the work; metal straight edges, angles, and bevels. The latter (bevels) are very important, as upon their accuracy depends the finished work. Bevels are of several varieties, and are generally set out by the mason to suit the particular work in hand.
Fig. 217. Problem IV.
Straight bevels require no explanation.
Twisting bevels are of various angles, and are set out from full-sized drawings made to scale for the particular stone requiring them.
Winding strips are bevels (see Fig. 218) for gauging the surface when required to twist (i.e. out of winding).
Dihedral bevels are required for setting out the angles formed by the junction of two plane faces. Templates are required for setting out the curves of soffit and extrados of an arch stones, and are struck to centres, or from the curves from which they are generated. Spirit-levels are necessary for setting up and trueing the work. Standards or rods divided into equal parts are used for marking off the courses of the stonework.