(b) Ink all circles, arcs, irregular curves.
(c) Ink-in horizontal lines with T-square and vertical lines triangle. Work from top to bottom and left to right.
(d) In this order ink-in inclined, dimension, extension and centre lines; arrow heads, figure, notes, title, section lines and border.
Before sending to the shop, a working draw ing must be checked for errors and omission, by an experienced checker.
To be effective the checking should be done systematically and with thorough concentration which allows nothing to distract attention. Observe this method: (1) Be sure that the views completely represent the object to be constructed and that they are properly arranged with respect to each other, according to the third angle method; (2) check all dimensions by scaling, and where advisable also by calcu lation. Dimensions of parts which go together should be compared. Also see that there are no interferences with adjacent parts and that proper clearances have been allowed. This is especially true in connection with mechanical movements, which should be laid out to scale so that the clearances are maintained; (3) the dimensions should be given as required by the shop; that is, the shop not be obliged to add or subtract to obtain any dimensions; (4) the proper finish marks f should be indicated and likewise the character of the finish desig nated; (5) all the necessary specifications of materials should be correctly given; (6) all small details, screws, bolts, pins, keys, rivets, etc., should be standard and where possible stock sizes should be used; (7) the title or rec ord strip should be checked to make sure that it contains in complete yet concise form all necessary details; (8) in connection with any points that have suggested themselves during this checking, the drawing should be reviewed in its entirety; (9) add any explanatory notes which from experience will enhance the effi ciency of the drawing; (10) before placing your Initials in the title space and assuming the re sponsibility for the accuracy of the drawing answer the question, I willing to sign this drawing as checked? Several kinds of one plane projection which result in a conventional picture have been de vised, so that the pictorial effect of perspective drawing is combined with the possibility of measuring directly the principal lines.
The third dimension is shown by turning the object in such a way that three faces are visible. Although these methods of representing objects have pictorial advantages their usefulness has some limitations. The representations are dis torted until the appearance is often unreal and unpleasant. Only certain lines can be measured and the execution requires more time, particu larly if curved lines occur. Nevertheless these methods are often used to great advantage in technical illustrations, patent office drawings, piping lay-outs, etc. The simplest of these sys tems is isometric drawing. If a cube is con sidered to be placed with one of its diagonals perpendicular to a plane, the edges of the cube will make equal angles to the plane of projec tion; and if an orthographic projection of the cube is made on the plane, the projection of the edges will be equal in length. The projections of the three edges which intersect (AB, CB, DB) at B will make an angle of 120 degrees to one another, as shown, Fig. 5. These lines are called isometric axes and are parallel to the directions of the three dimensions of the object The representations of edges which are parallel to these in space will be parallel to the isometric axes and are called isometric lines. In this projection all the lines have been shortened owing to the fact that they make angles to the plane of projection. If this fore shortening is disregarded and the full lengths laid off on the axis, the figure will be slightly larger but of exactly the same shape. This is known as isometric drawing and is used almost exclusively instead of isometric projection. It has the advantage of measuring the lines di rectly with ordinary scale, and the increased size is usually of no consequence. Lines not parallel to one of the isometric axes are called non-isometric lines. Measurements can be made only on isometric lines. If a non-isomet ric line is to be drawn, it must be drawn by reducing it to a system of isometric co-ordi nates. In this way curves of any shape may be constructed.