Mechanical and Free-Hand Drawing - Drawing Instruments - Drawing Scales - Plans - Elevations and Sections - Working Drawings of a Building - Free-Hand Sketches of Details.

Drawing Appliances - Board And T-Square. The principal appliances required by the pupil in the preparation of drawings used in building construction are (1.) The drawing board; (2.) The "T" square; (3.) "Set" squares and curves; (4.) Rulers. (1.) The drawing board is, for common purposes, well enough made of fir or pine; but for superior boards, a mahogany, bay wood, sycamore, or plane tree wood makes a capital board. The wood, of whatever kind, should be thoroughly seasoned, as damp or unseasoned wood is sure to warp when made up into the drawing board; and the preservation of a perfectly flat surface is for this, it need scarcely be said, a desideratum. The shape of the board is rectangular, that is, having a greater length than breadth. It may be made of any dimensions deemed advisable; where a wide range of drawing work is to be carried out, including detail drawings, as well as smaller plans and sections, it is useful to have several sizes of boards. For the work for beginners a useful one will be two feet long by sixteen to eighteen inches broad. The body of the board should be provided with cross pieces at each end, grooved at their edges, into which pass the tongues formed at the ends of the body or main surface of the board; the object of these cross pieces is to prevent the body from warping. In large drawing boards, the back is provided with a series of cross pieces having the same object in view. (2.) The " T-square " - This is so called from being composed of a thin blade or flat ruler, varying in breadth from one inch and a half up to three or four inches, according to the length of the square, and from three-sixteenths up to five-sixteenths of an inch in thickness. To one end of this the " head " or " butt" is secured at right angles, the two pieces thus assuming the form of a cross or " T," hence the name. In some forms of " T-square," the blade is fastened in the centre of the head or butt, so that on each side of the blade there is a recess formed, so that when the inner edge of the head is drawn along the edge of the drawing board, the blade will slide along the surface of the board at right angles to the head. In other forms of "T-square" the blade is secured to the upper side of the head, the sliding recess or rebate being thus below the blade. Another form of "T-square" is that in which the head is made in two thicknesses, lying flat one upon another, and connected together with a central thumb screw. The blade of the square is secured to the upper of these two pieces, and by means of the screw the lower half of the head can be adjusted to form any desired angle with the upper half of the head. The result of this arrangement is, that by sliding the lower half of the head along the edge of the board, the blade of the square will slide along the surface at the corresponding angle to which the head was adjusted. This form of " T-square " is very useful when a number of lines parallel to one another, but not at right angles to, or parallel with the edge of the board, are required to be drawn. When this form of adjustable "T-square" is used for ordinary drawing, when the head of the square is desired to be at right angles to the blade, it is necessary to see that the thumb screw is screwed tightly up to prevent the lower half of the head from separating and getting out of line with the upper half of the head. The use of the " T-square " in the drawing of lines on the paper secured on the surface of the board, will be now explained. Suppose the head of the square to be sliding along the lower edge of the long side of the board (which in practice is always placed next the draughtsman, or nearest the outside edge of the table upon which the board is placed while the drawing operations are going on), the blade at right angles to it is sliding along the surface of the paper, with its edges parallel to the ends, so that all lines drawn along the edges of the blade of the square will be at right angles to the side of the board; and all these lines, at whatever distances they may be from each other, will be parallel to one another. By shifting the square so that the head will now slide along the right-hand end of the board, the blade will slide along the surface of the paper with its edges parallel to the sides of the board, so that lines drawn along the upper edge, while they will be all parallel to one another, at whatever distances they may be drawn from each other, will be at right angles to the lines drawn when the blade was in the previous position, as before explained. When long lines are required to be drawn upon the surface of the paper or on the board, at right angles to each other, this shifting of the square so that its head shall slide along the lower edge and right hand edge of the board is necessary; but when short lines are required to be drawn at right angles to any line or lines drawn along the edge of the square when in any position, they may be drawn without shifting the position of the " T-square " by using (3.) the " set square" This is made of a thin piece of hard wood, the edges of which are made perfectly smooth and square - that is, at right angles to the surface; the form is usually a " right-angled triangle " - that is, at which the hypothenuse is at an angle of 45° to the base. By sliding the base of this along, and keeping it in close contact - which can easily be done with a little practice - with the edge of the " T-square " lying in accurate position on the board, all lines drawn along the " perpendicular " of the " set square " will be at right angles to the lines drawn along the edge of the " T-square," so that these lines can be drawn without shifting the " T-square." When this " right-angled triangle " form of " set square " is used, all lines drawn along its hypothenuse will be at an angle of 45° to those lines drawn along the edge of the " T-square," the base of the " set square" sliding as before along the edge of the " T-square." Other forms of " set squares " are used; a very commonly used one having the hypothenuse line forming an angle of 60° with the base line, this form being useful in putting down isometrical drawings (see Technical Drawing p. 7.) " Curves" are pieces of thin hard wood, the edges of which are cut to various curved lines, the interior surface having also cut out from it portions, the edges of which also form various curved lines. These are useful for drawing curves not easily or conveniently described by the compasses, or which form part of eccentric curves not describable by compasses. Those are to be had in great variety. (4.) "Rulers" are made of two kinds - " ordinary " and " parallel." " Ordinary rulers " made of hard wood are flat, and of various lengths and breadths, and are useful for drawing lines between points to which the " T square " is not conveniently applicable. One of the edges of the ruler is often made with a bevel, but we prefer both edges to be square to the face. The edge of a " set square " affords a good ruling surface, if long enough. " Parallel rulers," as their name indicates, are for drawing lines parallel to one another, to which the ordinary " T square " is not applicable, or not conveniently so. They are of two kinds - the old fashioned, consisting of two blades, connected by brass links; and the single ruler, with wheels or rollers at each end. This is the modern form of the instrument; and when the draughtsman becomes accustomed to its use, it is very much quicker in its operation than the double-bladed parallel ruler. But a beginner is apt to make mistakes in its use, hence by some the old-fashioned ruler is preferred.