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Preparation of the Materials Stone Cutting

bed, surface and bottom

PREPARATION OF THE MATERIALS. STONE CUTTING.

Dressing the Stones. The stonecutter examines the rough blocks as they come from the quarry in order to determine whether the blocks will work to better advantage as a header, a stretcher, or a cornerstone. Having decided for which purpose the stone is suited, he prepares to dress the bottom bed. The stone is placed with bottom bed up, all the rough projections are removed with the hammer and pitching tool, and approximately straight lines are pitched off around its edges; then a chisel draft is cut on all the edges. These drafts are brought to the same plane as nearly as practicable by the use of two straight edges having parallel sides and equal widths, and the enclosed rough portion is then dressed down with the pitching tool or point to the plane of the drafts. The entire bed is then pointed down to a surface true to the straight edge when applied in any direc tion—crosswise, lengthwise, and diagonally.

Lines are then marked on this dressed surface parallel and per pendicular to the face of the stone, enclosing as large a rectangle as the stone will admit of being worked to, or of such dimensions as may be directed by the plan.

The faces and sides are pitched off to these lines. A chisel draft is then cut along all four edges of the face, and the face either dressed as required, or left rock faced. The sides are then pointed down to true surfaces at right angles to the bed. The stone is turned over bottom bed down, and the top bed dressed in the same manner as the bottom. It is important that the top bed be exactly parallel to the bottom bed in order that the stone may be of uniform thickness.

Stones having the beds inclined to each other, as skewbacks, or stones having the sides inclined to the beds, arc dressed by using a bevelled straight edge set to the required inclination.

Arch stones have two plane surfaces inclined to each other; these are called the beds. The upper surface or extrados is usually left rough; the lower surface or intrados is cut to the curve of the arch. This surface and the beds are true by the use of a wooden or metal templet which is made according to the drawings furnished by the engineer or architect.