In Fig. 97 is shown a very common form of drawing board, consisting of a pine wood top with hardwood ledges. The ledges are put on by means of a dovetail, tapering probably one-half inch in the width of the board, so that while allowing entire freedom for seasoning there is no danger of cracking the board, and they may be driven tight as required. Where it is desirable to use screws in the ledges they are passed through slotted holes furnished with a metallic bushing.
Fig. 97. - Drawing Board, with Ledges.
In Fig. 98 is shown a still simpler form of board. which is adapted only for the smallest sizes. Hardwood strips are tongued and grooved onto the ends to prevent warping, as shown in the engraving. By using strips of wood thicker than the board, keeping their upper surfaces flush with the surface of the board, it may be constructed so as to have the advantage of ledges on the under side equivalent to those shown in Fig. 97.
Fig. 98. - Drawing Board, with Tongued and Grooved Cleats.
Fig. 99 shows a construction which, while being somewhat more expensive than the others, is undoubtedly much better. It is made of strips of pine wood, glued together to make the required width. A
Fig. 99. - Bottom View of Drawing Board, with Grooved Back and Cleats Attached with Slotted Holes.
Drawing Tools and Materials. 19 pair of bard-wood cleats is screwed to the back, the screws passing through the cleats in oblong slots with brass bushings, which fit closely under the heads and , yet allow the screws to move freely when drawn by the shrinkage of the board. To overcome the tendency of the surface to warp, a series of grooves are sunk in half the thickness of the board over the entire hack. To make the working edges perfectly smooth, allowing an easy movement with the T-square, a Strip of hard-wood is let into the end of the board. The strip is afterward sawn apart at about every inch, to admit of contraction. In the construction of such boards additional advantage is obtained by putting the heart side of each piece of wood to the surface.
As pattern cutting is nothing if not accurate, it is a matter of the utmost importance that the drawing board or table should be perfectly rectangular. If each angle is a right angle - if its opposite sides are exactly parallel - the T-square may be used at will from any portion of it with satisfactory results. If the board is accurate the drawing will be accurate If the board is not accurate the drawing can only be made accurate at the cost of extra trouble and care. While it is easy to get a board approximately correct by ordinary means, one or two simple tests will serve to point out inaccuracies for correction which by ordinary means would pass unnoticed. For such tests a T-square and an ordinary two-foot steel square that are exactly correct will be required.
Fig. 100. - Testing the Sides of a Drawing Board.
Having made the opposite sides and ends of the board as nearly accurate as possible, place the head of the T-square against one side, as shown in Fig. 100, and with a hard pencil sharpened to a chisel edge, or with the blade of a knife, scribe a fine line across the board. Then carrying the T-square to the opposite side of the board, as shown by the dotted lines, bring the edge of the blade to the line just scribed and see that it exactty coincides throughout its length with the line. Repeat this operation at frequent intervals along the edges of the board, both at the sides and ends. Remove any small inaccuracies on the edges by means of a file or line sand paper folded over a block of wood. Careful work in this manner will produce very satisfactory results.
A means of testing a board with reference to the accuracy of the corners is shown in Fig. 101. A carpenter's try-square or an ordinary steel square used upon the corners does not ordinarily reach far enough in either direction to satisfactorily determine that the adjacent end and side are perpendicular to each other; hence it is desirable to obtain some kind of a test with reference to this point from the middle portions of the edges. With the head of the T-square placed against one side of the board draw a fine line, as indicated by the dotted line in the engraving, and from one end draw a second line in the same manner. If the side and end are at right angles the two lines will coincide with the arms of a square when placed as shown in the engraving. Repeat this operation for each of the corners. The two methods above described for testing drawing boards, especially when used together, cannot fail to enable any one to obtain a board as nearly accurate as it is possible to make it. Modifications of the methods here given, and based upon the same principles, will suggest themselves to any one who will give the matter careful thought.
Fig. 101. - Testing the Corner of a Drawing Board.
Straight-Edges. - In connection with every set of drawing instruments there should be one or more straight-edges. If nothing but pencil or pen lines are to be made upon paper, those of hard-wood or hard rubber will answer very well; but if lines are to be drawn upon metal, steel is the only satisfactory material. The length of the straight-edge must be determined by the work to be done, but a safe rule is to have it somewhere near the length of the table or hoard. Of course this is out of the question in cornice work, where tables are frequently upward of twelve feet in length. In such cases the size of the material to be cut determines this matter. If iron 96 inches long is used, the straight-edge, for convenience, should not be less than 8 1/2 feet. If shorter iron is regularly used, a shorter straight-edge will answer. In cornice work, two and even three different lengths are found advantageous. The longest might be as just described; a second might be about four feet in length and made proportionately lighter, while the smallest might be two feet and still lighter than the four-foot size. Instead of the latter, however, the long arm of the common steel square serves a good purpose.