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.
The bricks have now to be cut to the shape of the template, the operation of cutting being performed in the following manner: The bricks are bedded and faced in the manner shown for plain gauged work. The top bevel is then taken from the template with a bevel square, and the head of the brick is scribed to this bevel with a tin saw, as shown at A, Fig. 185. The ends of this scribed bevel are squared and scribed across the bed and cutting side of the brick, and the head is rubbed down to these lines. A wooden lengthening box is then made 8 inches in length, as shown at B, Fig. 185, and the bevelled head of the brick is placed tightly against the end of the box, and the end of the brick is cut off with a bow saw run down the open end of the box as shown. This gives the soffit bevel to the bricks. Boxes are usually made to take two bricks at a time.
The arch ring under consideration is 1 foot in depth, while the brick dealt with is only 8 inches deep, and must therefore be made up by 4 inches. To do this a 4 1/2-inch bat is taken, and is "bedded," "faced," and "bevelled" and cut off to 4 inches in length in a lengthening box. The 8-inch lengthening box already made will do for this purpose if a fillet of wood be nailed to its bottom 4 inches from the open end.
A radiating box C (Fig. 185) is now constructed, the sides of which, above the bottom, are shaped exactly like the template, and are placed with the cutting marks exactly opposite one another. The 8 and 4-inch bricks are then laid bed downwards in this box, and cut with the bow saw worked along the edges, and trimmed with a file.
Radiating boxes are usually made about 10 inches wide, so that two bricks may be cut at a time - one for the right hand, the other for the left-hand side of the arch.
The bricks are next laid upon a chopping-block (D, Fig. 185), and the frogs connected up and a cement channel cut in the upper end, the tool employed for cutting being a scutch (Fig. 174), which is formed of an old flat file sharpened at the end and fixed into a stock. If there be no frogs in the bricks the beds are cut out for cement joggles.
All the voussoirs of the arch are framed in a similar manner, and the arch is set over a centre.
Lime putty similar and similarly applied to the bricks as in plain gauged work is used for the joints, the grout channels being filled up with cement mortar when all the voussoirs are in position. The brick is then placed in position and lightly tapped to make it take a proper bearing.
Gauged arches should be built up from both sides, the key being inserted last, after which all the joints are thoroughly grouted up with cement and the putty trimmed flush with the face of the bricks.
To mould the soffit of a brick arch the above operations are only affected so far as the lengthening box is concerned. The two pieces of wood for forming the sides of the box are taken and screwed together, and the one end cut to the shape of the desired moulding. They are then separated and fixed exactly opposite one another at the sides of the lengthening box (E, Fig. 173). The bedded, faced, and bevelled bricks are placed in this box as before, and the ends are cut off to the shape of the moulding and trimmed, the straight parts with a file and the curved parts with a piece of gas barrel.
The setting out and cutting of segmental arches is precisely the same as for semicircular arches, but a small difference arises here in the cutting of the skewback. To cut the skewback accurately a wooden reverse called a Gun is made as shown in Fig. 176, the angle cab being equal to the angle formed by the jamb and the skewback, as obtained from the full size setting out. The gun is used in the following manner: The bricks from which the skewbacks are to be formed are laid dry in their places. The limb of the gun L is laid along the face of the jamb with the point a adjusted to the springing point of the intrados of the arch. The bricks are then scribed to the line ab removed and cut.
In flat arches (see Fig. 176) the method of setting out is somewhat different. The extrados and intrados are set out as before, the intrados being divided into the same number as the extrados. The only difference in cutting is that the bevels of each brick are different.
The skewbacks of flat arches are usually inclined to one another at an angle of 60 degrees, but a stronger arch is obtained if the skewbacks expand 1 inch for every foot in the width of opening.
All arches sag a little when the centres are removed, and sagging in the case of a flat arch is most unsightly, for which reason it is usual to give so called flat arches a rise of 1/8 inch for every foot of span.