Drafting Materials. Mstrunzents. The drafting instruments required are: A drawing board, T-square, triangles of various kinds as noted below, pencils, scales, erasers and erasing shields, a set of drawing instruments, a large linen cover, and half sleeves.
The drawing board should be made of soft pine with battens upon the back in order to prevent the warping of the board. Since few drawings in structural engineering are larger than 24X 36 inches, it is not necessary to have the drafting board larger than 26X3S inches. A drafting board should not lie close to a table, but should be raised from the table by small legs placed at its upper edge as indicated in Fig. 2.
The T-square should be about 40 inches in length and should be of good quality with an amber edge upon each side. The amber edge is of great advantage since it will allow the draftsman to see lines below that one which he is drawing and, therefore, prevent him from overrunning by drawing one line past its limiting point. Such a T-square may be procured for about 62.25.
The triangles should be of amber or celluloid, and should con sist of the following: One 4.5-degree triangle with 10- or 12-inch sides; one smaller, say with 6-inch sides; two 60-degree triangles with 10-inch sides; and two with 4-inch sides. One or more of these triangles should have the beam and coping bevels fixed upon it as in Fig. 3; this will have to be done by the draftsman, since no such triangles are on the market.
The pencils used by the draftsman should be such as will make clear and black lines upon paper in case the drawing is to be traced. If the drawing is not to be traced, a harder pencil will suffice. In case a drawing is made directly upon tracing cloth, a soft pencil should be used and it should be kept sharpened. This will neces sitate frequent rubbing over the sand paper pad which every drafts man should have close at hand in order to keep a good point upon his pencil. The pencil recommended for detailing where a tracing is to be made is "Koh-I-Noor, 3 FI," although some draftsmen prefer 4 H or 5 H. The latter are, in the writer's opinion, to be recommended for detailing where a tracing is not required from the original. In case drafting is done directly upon tracing cloth, a 2 H pencil is the correct one to use.
A red pencil should be kept for marking upon blue prints and a blue pencil for making checks on tracings. Never use a red pencil
upon tracing cloth, since it will not be easy to erase, v hereas the blue-pencil mark may he washed di with gasoline or erased with a pencil eraser.
The scales required are the architect's and the engineer's. The former has certain divisions upon it and each of these divisions is divided into twelve parts which indicate inches, and these parts are in turn divided into halves or quarters or other small divisions denoting the fraction of the inch. The architect's scale which best serves the purpose is the one which has the 2-inch, 11-inch, 1-inch z inch, inch, 8-inch, i-inch, h-inch, and scale. A special scale for the making of drawings to a large size or for the making of layouts is a great convenience. Such a scale is on the market and is divided so that half of an inch is equal to one inch. This scale should be in the outfit of all checkers. The engineer's scale is one on which the inches are divided into certain decimal divisions. The best scale for this is that which has its edges divided into 10, 20, 40, 50, and GO parts of an inch. This scale is of use only in laying off bevels and natural functions of angles or in draw ing outlines upon which details will be constructed with the use of the architect's scales. The tendency of young engineers to use the engineer's scale, allowing a certain decimal to equal a certain fraction of an inch, is to be discouraged Lecause of the liability of error, and a severe penalty imposed for a second offense. Care should be taken in the use of scales such as the architect's which have different scales on the same edge in order not to get the feet which belong to the wrong scale.
A small paper clamp should be attached to the scale a short distance from the center opposite the end where the scale which the draftsman is using is situated. This will prevent the scale from being turned over, hence avoiding any other scale, but the one the is using at the time, turning up. Also when the draftsman picks up the scale by the paper clamp, the end on which the scale he is using is situated will tilt downward and at once indicate to him which end he should place in position to measure what he wishes. Fig. 4 shows one of these clamps in position for the scale as indicated.