To "dimension" working drawings is to place measurements upon the parts represented, to enable the workman to proceed without measuring the drawing itself.

These dimensions should be placed so as not to interfere with nor crowd the lines of the drawing, nor yet interfere with one another.

Arrow-heads are used at the extreme points of measurement, the figures are generally inserted midway between the arrows; a dot and dash line reaches from the figure to the arrow-heads, as shown below.

Arrow-heads and figures should be drawn free-hand with a common writing pen.

Usually dimensions are given in inches, up to 24 inches, as it is found less confusing; for instance, if written ' ' it may be mistaken for II"; if written 13" no mistake could be made.

Again, 'o' may be mistaken for 10"; if written 12" it would not; in addition to being more distinct, it occupies less space on the drawing. In large measurements there is more room for the figures, and, therefore, they can be spaced further apart-in feet and inches.

All figures should be made of a fairly large size. Vertical dimensions should read from the right hand, thus, as shown:

Measurements of importance, such as the diameter of a circle, the pitch or distance apart of rivets and bolts, etc., should be marked in figures on the drawing. When rough or unfinished work is mixed with

Ddiam. of shaft, 24 inches.
L-length of bearing, 34 inches.
T-thickness of collar, inch.

D-diam. of collar, 3 incl.es.

Generally it is preferable to give the diameters of turned and bored work on a section, instead of an end drawn separately; confusion is sometimes caused by a number of radial dimensions,

Fig. 242 and fig. 243 are introduced to show the principal measurements required in practical work, and the usual way in which such dimensions are marked when ordering parts of machinery.

Fig. 242 is a pedestal, or metal frame; three views are shown, the center figure being an elevation, the lower figure is the plan of the base, the upper figure is a view of the top, on which is bolted the bearing block, it being on the outside of the center figure. The essential measurements are marked by letters. His the vertical height from base to the seat of bearing block L being the length, and W the width of the base; P is the length between checks, and B the width of seat for bearing block; C is the distance from center to center of the holding down bolt holes, and T is the depth of the holes in the base; K is the distance from center to center of the bolt holes in the top for bearing block.

Fig. 243 is a hanger, or metal bracket, and shows the center figure or elevation, the plan of the top and the plan of the seat for bearing block, which is bolted on the interior of the center figure. His the vertical distance from the top to the seat for bearing block; the other measurements required are marked by letters similar to figure 242.

ures.

Now, one of the important matters in connection. with dimensioning a drawing is the location of the figOne rule, whose utility cannot be gainsaid, is that they should be so located that they can be altered. or erased without damage to the lines of the drawing, as changes may be necessitated either by original errors in writing down the figures or by changes in the design being found desirable during the construction of the machine.

To produce an effect, drawings are shaded; that is, shadow lines about twice the width of the regular line are drawn according to a recognized rule, which always represents the same peculiarity of form in the

same way.

In working drawings light lines only are permitted; shade lines are wider than the working lines, and in reading scale measurements` the extra thickness of line would make a difference.

Instead of representing the shadow as it is really cast by the object, the edges which cast the shadow are determined, and all the views are treated as if the light came from behind and from the left, downwards, at an angle of 45° to the horizontal line, as shown by the arrows in figs. 245 to 248.

The lower and right-hand outlines of projecting parts will cast shadows, and the student should make them of extra width.

Fig. 245.

Fig. 246.

Fig. 247.

Fig. 248.