In every branch of drafting and mechanical drawing lines are standardized. A particular kind of line always means a certain thing, regardless of whether it is straight or curved or pencilled or inked. These lines are shown below, together with their application in a simple drawing. Line A is a medium-heavy solid line, always denoting the visible outline of any object.

Line B is a medium-heavy dotted line (very small dashes), always denoting invisible outlines—parts behind other parts.

Line C is a medium-heavy long-and-dash line, always denoting the center line of a drawing. Frequently you will see half of the drawing finished and a note: "symmetrical about this center line."

Line D is a very light line extended from the main drawing for the purposes pf enclosing some dimension. It must never touch the main drawing, but it must come very close, as shown.

Line E is a very light line, broken in the center, with small arrowheads at each end to show a dimension. The dimension is given in the space in the center. The correct and incorrect way of making the arrowheads is shown below the lines.

Line F is a heavy, long and two dash-line to indicate sections. Wherever this line appears on a drawing, it shows that a section of the drawing at that part is given somewhere else.

Only the first two lines may be curved, although line E, when giving the dimensions of a circular arc, may also be curved. It is very important to know these six lines thoroughly because all your future work will include them.

ORDER OF WORKING-INKING IN A DRAWING

Next to accuracy and neatness, orderliness is the most important requisite of a good draftsman. You must learn to do things in the most efficient order, because if you don't, you are sure to waste a lot of valuable time and you may get yourself into serious trouble. In all your drawing, the following order must be followed:

PENCIL

1. Be sure that your instruments are clean—no dirt or ink on the triangles, protractor, T-square or French curves. Be sure that the ruling pens are clean and that your drawing board is free from any pencil sharpening or dust.

2. Either tape or thumb-tack your paper on your board; then draw an inch margin all around the paper.

3. Find the center of your paper horizontally and vertically, and make a small cross with your pencil at this point.

4. Figure out the most convenient scale for your drawing. Then decide how you are going to place the drawing on the paper with relation to the center mark.

5. Draw a very light horizontal line near the bottom of your paper; use this line for all horizontal measurements.

6. Draw a very light vertical line to the left of your paper; use this line for all vertical measurements.

7. All measurements must be extended by very light pencil lines by means of the T-square and the triangles.

8. When drawing circles and arcs, be sure that the needle point of the compass does not go too deeply into the paper.

INK

9. Ink all small circles and arcs with bow pen compass.

10. Ink all large circles and arcs with compass.

11. Ink all dotted circles and arcs.

12. Ink all compound or irregular curves with French curve.

13. Ink all horizontal full lines.

14. Ink all vertical full lines.

15. Ink all full lines at angles to horizontal.

16. Ink all dotted lines.

17. Ink center lines.

18. Ink in very fine lines and all extension lines.

19. Ink in very fine lines and all dimension lines.

20. Add small arrowheads to all dimension lines.

21. Letter in all dimensions and other lettering.

22. Ink in section lines, if any.

23. Ink in border with very heavy line.

LAYOUT OF DRAWINGS

In addition to the rules for penciling and inking given previously, the draftsman must have a definite system of layout. On the next two pages we show typical examples of the various steps taken in the layout of a drawing. Opposite we see a drawing of a punched-out plate with all dimensions given; in the six boxes beneath it we see the various steps used in the preparation of this drawing.

The first thing to do is to find the center of your paper. You do this by drawing two very light diagonals from the opposite corners of the paper. Where these diagonals meet will be the center of the paper; a light cross should be made at this point, as shown in Box 1. Since the outside dimensions of this plate are 4" x 6", and the scale is half-size, we measure l½ inches on either side of the cross horizontally, and 1 inch on either side of the cross vertically; we then block in the rectangle shown in Box 2.

The next thing to do is to put in the center marks of the four round corners. As you can readily see, these corners are arcs, and the radius is given as ¾ of an inch. This means that in the half-size drawing these center marks must be a of an inch in from the horizontal and vertical lines, as indicated in Box 3. The two center circles are also to be put in, together with the rectangular slit. If you look at Box 3, you will see these six centers penciled in and ready to be inked. In Box 4 we see the side pieces blocked in. We also observe that the arcs of these circles are now inked in. You can see the four heavy corner arcs and the two middle circular arcs.

When you have completed inking in the circular arcs, the next thing to do is to ink all horizontal lines, as shown in Box 5. After this is done, ink in the vertical lines and erase all pencil lines. The result is the completed drawing shown in Box 6.

On page 44 we see a drawing of a wrench. In it you will note two hexagonal cuts, the left cut being larger than the right one, and the centers being separated by a distance of four inches. The outside of this wrench is circular and the various radii are all given on the drawing. Here again, find the center of the paper as you did before, and lay off the two center marks of the circles to the right and left of this center, as shown in Box 1. Box 2 shows the location of the connecting arcs of the two circles. Lines are drawn from the centers at 45 degrees to two vertical lines ¾ of an inch apart. Where these 45-degree lines intersect the vertical lines we have the centers of the four arcs. These four arcs should now be inked in as indicated.

In Box 3 we see the completion of the circular arcs, using the two centers given in Box 1. We have now inked in most of the outline of this tool. In Box 4, two smaller circles are drawn from these two centers, and are marked off in six equal parts by means of the 30-60-degree triangle. These marks determine the hexagons which are shown inked in in Box 5. After these hexagons have been inked in, the two horizontal connecting lines are then inked, and all pencil lines are erased to give the final completed drawing of the tool, Box 6. This drawing, of course, is half-size.

As you draw, be sure to remember that all pencil lines must be extremely light so that they may be easily erased. You must also make sure that your order of inking follows exactly the order given on page 42, and that all lines conform with the standards set forth on page 41.

At the completion of each drawing, ink in a heavy border line around the entire drawing, leaving an outside margin of about 1 inch.

DIMENSIONING

So far, we have said nothing about dimension lines. This is because, as you will soon discover, dimensioning is a subject all by itself. We have, however, mentioned the arrowheads and the thickness of dimension lines. You know by now that dimension lines must be kept very faint, as shown in line D on page 41.

The main object of dimensioning is clarity.
 
And nothing must be sacrificed for clarity. For this reason dimensioning is more a matter of common sense and good judgment than it is a matter of rule and regulation.

There are a number of guiding principles for dimension lines which are based primarily on experience. These principles must be observed wherever possible. For instance, horizontal and sloping dimensions should always read from left to right; vertical dimensions must read from bottom to top. This simply means that all vertical dimensions must be read from the right side of the paper instead of the left. Figure 24 gives the incorrect way of dimensioning, Figure 25 the correct way.

Wherever possible, all dimensions must be kept outside the main drawing. An exception to this rule is permitted only when added simplicity and ease of reading are gained by placing them inside the drawing. Where a number of horizontal dimensions are given, they should be staggered, as shown in Figure 26.

Always break a dimension line in the middle to allow for the dimension figure. The one and only exception to this rule occurs when a part of the drawing projects down, and interferes with the figures. Of course, in this particular case, the dimension figure must be placed to one side (Figure 27). Dimensions of circles should always be given from the centers of the circles, and the diameter of the circle should be written in small lettering along the circumference (as, D — 5 inches; Fig. 30). In giving parts of circles, or circular arcs, the radius rather than the diameter is frequently given. Thus we have R = ¼-inch. This is often indicated by an arrow radius.

A number of dimensions in a horizontal row may either be continuous or staggered; the usual method is a continuous line, as shown in Figure 29.

Never crowd dimensions. If a given space is too small for a given dimension, show the arrowheads and a curved line bearing the given dimension, as in Figure 28. The dimensions of an angle should always be shown in the form of a curved arc, as in Figure 31.

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