Up to this point we have: been considering only the so-called board equipment which is made up of the drawing board, the T-square, two triangles, some good scales and some 2H pencils. The only "outside" implement we have discussed is the protractor, but nothing has been said about the set of instruments.

If you look at picture 5 on page 6 you will see a number of instruments in a case. The three instruments on the right are shown enlarged in drawings 7, 8 and 9 below—7 is a small dividers, 8 is a pen bow compass and 9 is a pencil bow compass. The first long instrument at the top left of the case (5) is a ruling pen, the most important of all the draftsman's instruments. It is shown enlarged in drawing 6. The two instruments at the bottom left of the case are a large dividers and a large compass. In 10 we see a combination of dividers, pencil compass and pen compass. The pencil and pen attachments are shown separately. The piece directly below the ruling pen in the case is an extension arm for the compass, for the purpose of making very large circles. Directly below this is a small metal case for extra leads for the pencil compass. Other important equipment shown on the page are the French curves, 17, and the flexible curve, 13.

In order to use these instruments we must become thoroughly acquainted with each. We must not only know what each is used for and how to use it, but we must also know how to keep it in good condition so that it will always be ready to give satisfactory service.

The Ruling Pen

So far everything that you have drawn has been in pencil. You have not inked in anything, and it is assumed that as yet you have not used a ruling pen. It is now important to learn how to rule lines with this apparently simple instrument. Don't be surprised if you are not successful at the very outset. To rule good clean lines requires a great deal of practice. It is something like learning to ride a bicycle. At first you will be "wobbly" and your lines will be uneven and broken, but once you "get the hang of it" you will use a ruling pen without even thinking about it—any more than a bicycle rider thinks about balancing himself or a chauffeur thinks about how to apply the clutch or brake in an automobile.

The first thing to do is to take the ruling pen, Figure 7a, in your left hand and turn the little screw S back and forth several times, noticing how it makes the distance between these two prongs wider or narrower. Now get the two prongs almost to meet, and then fill the pen in the following manner:

Remove the cap from the bottle of India ink and place the tongue of this cap between the two prongs, as shown in the picture. The ink from the cap will partially fill this gap and your pen will be ready for use. DON'T FILL IT TOO FULL! See illustration.

Now hold the pen vertically, sliding it against the T-square, as shown in the left-hand picture. If no line appears, turn the screw slightly and try again. When the ink starts to flow, a steady line will result as you move the pen along the paper. The thickness of this line will depend upon the little screw which determines how far apart the two prongs are. If the prongs are wide apart, the line will be very thick; if close to each other the line will be very thin. You can regulate the thickness of the line to any degree you wish. Here is the first DON'T: don't have the screw too tight because the two prongs will be forced together and no ink will flow; you won't get any line at all. The second DON'T is: don't hold the pen as shown in the right-hand picture because the ink will not come out evenly and you will get a line of varying thickness with an inevitable smudge at the end of it. The third DON'T: don't press down too hard on the pen. It will rule evenly without a lot of pressure. Just draw the pen across the paper as you would a pencil; if you hold the pen correctly (as shown in the left-hand picture) your line should be clear and even throughout.

Practice ruling lines with the pen. Rule a few dozen lines and then turn the screw to get a thicker or thinner line. Rule a few dozen lines and turn the screw again. Do this over and over and over again until you feel that you can draw good clear lines like those shown under the left-hand picture and NOT like those shown under the right-hand picture.

Now turn back to Lesson 3 and ink in the diagrams with your ruling pen. Then carefully ink in the pencil drawings which you made in Lesson 6. YOU CANNOT PRACTICE THE USE OF THE RULING PEN TOO OFTEN. It is a positive MUST to be able to rule clean, clear lines, and the more you practice the better able you will be to do this.

When the pen is not in use, be sure that it is clean. Never put any instrument away without cleaning it thoroughly, for when ink dries on a ruling pen it clogs it, and when you fill it the next time, the dried ink prevents the flow of fresh ink so that your line is sure to be uneven and blotchy.

Summary Of Don'ts

1. DON'T fill the ruling pen too full.

2. DON'T have the prongs tight against each other.

3. DON'T slope the pen away, or toward the edge of the T-square.

4. DON'T use a blotter for lines.

5. DON'T press too hard on the pen.

6. DON'T ever go backward on a line.

7. DON'T let ink dry in the pen.

8. DON'T use a scale for a ruler.

9. DON'T use T-square or triangles for guides in knife cutting.

10. DON'T move the T-square when the line is wet.

11. DON'T put the bow instruments away without widening them and releasing tension on the springs.

12. DON'T draw with the lower edge of your T-square.

13. DON'T leave the ink bottle uncorked.

14. DON'T use the dividers for anything but dividing distances.

The Compass-Curved Lines

All your work so far has been done with two triangles and a T-square. All the lines that you have drawn have been straight lines.

Now we shall discuss the compass and the French curves and curves in general, so that when you have finished reading this section you will be thoroughly familiar with the drawing of circles and curved lines.

The large compass is shown in Figures 8, 9 and 10. It usually comes in the compact unit shown in Figure 8 which pictures a pencil attachment P, a pen attachment R, and an extension arm E, to the main unit which consists of the dividers.

Figure 9 shows the compass with the pencil attachment. The pencil is attached by unscrewing screw A, removing the divider, inserting the pencil unit and tightening screw A. The units pivot about D so that they may be moved to be vertical with the paper as shown. The screw B permits you to make the length of the lead longer or shorter, and the screw C does the same for the needle point. Figure 10 shows the same compass with a pen attachment. In drawing circles it is important to keep the units vertical, as shown in the diagrams. The pictures below the compass show how to use the compass.

The compass will draw circles from l½ inches in radius to about 7 inches. If you want a larger radius you may use the attachment arm E in Figure 8. This lengthens the radius so that circles up to 10 ½ inches in radius may be drawn with the aid of this arm.

In order to measure a radius accurately, place the compass against the ruler (as shown in Figure 9), so that the needle point is at the zero mark and the pencil or pen is at the required radius. The figure shows a pencil compass set for a radius of 1 11/16".

Figure 11 shows the three bow instruments. Figure 11a shows a bow pen compass, lib shows a bow pencil compass, and lie shows the dividers. These three instruments are made adjustable by the screw S. By turning this you can lengthen or shorten the radius of the circle. Circles 1/16" in radius to more than an inch in radius may be drawn with the bow compass. This compass is used for very small arcs such as rounded corners and edges and bottoms of test tubes, etc. It is chiefly used for denoting screws, rivets and small holes in shop drawings.

The dividers are used for trial purposes. If you want to divide a line or a circle into any given number of parts, you usually set your dividers to "about" the size of the unit part and move it step by step. (First one needle point, then the other, somewhat the way you walk.) If the number of divisions comes out evenly —if there is no space left over—well and good; but if there is a left-over space you must readjust the radius of the dividers accordingly and try again. Note that the dividers makes no mark, since the instrument is neither a pen nor a pencil. It simply gives an indication of how the given lines are to be divided equally and must be used by the trial and error method. There is another and more important use for this instrument. If you wish to reproduce a line drawing from another drawing, or a plan from another plan, use the dividers instead of the ruler. It is much more efficient to get. the exact length of a line with the dividers than it is to measure it and reproduce the measurement.

On the opposite page are shown some figures which are given you for practice. Note the difference in the top row of concentric circles. The first series shows a number of circles, all on the same center and all of the same thickness. The second series shows the same thing with varying thickness of lines. The third circle (Figure C), shows the "shading" on a sphere. Note how this is done. The circles are not complete, and they grow less and less complete as they approach the center. They also are wider apart as they approach the center, and they are all very thin lines.

Now look at Figures D and E. They demonstrate how to draw round corners on an oblong, and also how to connect straight lines with small arcs. It is very important to remember that, when you have straight lines connected to small arcs, you must draw the arcs first, as shown in D and E, and then connect the lines to them, as shown in D' and E'. Never draw the straight lines first and the arcs connecting with the lines; you will not be able to show a smooth, even line if you do this.

Figure F shows a number of thin curved lines drawn with the extension arm of the large compass.

Practice drawing all these figures. Do them in pencil first and then ink them in. Use the bow compass on all of them except F. For F you will have to use the extension arm attachment with the large compass. After you have copied these figures, make up some of your own. Draw the concentric circles closer together with the thinner lines. Shade the sphere differently (on the other side), and reverse the thick and thin circles in Figure B, making thick lines in the middle and thin lines on the outside and center portion. This will give you excellent practice in the use of the bow compass. Be critical of your work. If you have a straight line just missing a connection with a small arc, do the work over until the line runs smoothly into the arc.

Figure G will give you good practice in the use of the large compass, and possibly the extension arm attachment. The figure shows two car tracks with a switch and a curve. It is drawn to a scale of 1 inch equals 20 feet; if you examine the switch you will see that the first has a radius of 60 feet, then comes a straight portion, and the other has a radius of 100 feet. You can draw this by drawing a vertical line where the switch commences, measuring off 3 inches on that line. This will be the center of the curve which must be swung until it comes about half-way between the two tracks. Now measure off 50 feet (2½ inches) along the tracks and do the same thing for the other curve, drawing the vertical line in the opposite direction and measuring off 5 inches (100 feet) instead of 3 inches. When you have drawn the two curves, connect them with straight lines, as shown. The large curve starts where the switch ends. Draw a vertical line again and measure off 8 inches (160-foot radius), drawing the curves as shown.

On the next page we see some compound curves, spirals and ellipses. These compound curves and spirals are done with the compass and the bow compass. Note Figure H. It starts off with a radius of 3 inches and swings through an arc of 30 degrees; then the radius is shortened to 2 inches and a new arc is swung through the same angle, after which the radius is again shortened to 1 inch and a new arc is swung. As you can see, this gives a continuous compound curve. Be careful to have these curves connect exactly so they form a smooth, continuous curve. Now draw the two spirals shown in J and K, measuring the centers A, B, C, D, etc., and using them to draw your arcs as shown in Figure H.

Compound curves are extremely important in drafting. They are so frequent that the use of the compass is often impractical, and most draftsmen resort to French curves, or the flexible curve shown in Figure 13 on page 6. The use of the French curve will be explained presently, but in the meantime it will be valuable to you to know how to draw these curves with a compass. A typical example is shown on page 29. Here, at the upper right-hand corner of the page, we see the design of a pitcher in rough sketch. All the information necessary for an accurate drawing of the object is given on that sketch. Study it carefully and note the various radii. (The letter R stands for radius.) Now study the finished drawing which is just half full-size. Measure the radii of the various curves, being sure to double them in order to check the drawing. To take an example: the top of the pitcher has a curve that shows a radius of 11 inches. Measure the radius of this curve on the finished drawing; you will see that it is 5½ inches—just half-size. Check the other measurements on the drawing against the sketch dimensions, and note particularly the use of the compass to draw the compound curves.

Referring again to the page opposite, you will see two ellipses. They are not true ellipses but are near enough for practical purposes. They are made as follows: Draw a horizontal line xx and a vertical line yy. At the intersection point O, draw a circle cutting line xx in A and B. With A and B as centers, draw two circles, as shown. The center circle or the two intersecting circles also cut the line yy in C and D. With these points as centers draw the upper and lower arcs, connecting the circle on A with the circle on B. The resulting figure will resemble an ellipse. Other methods of drawing ellipses are given in a later section.

The French Curve

In mechanical drawing we have just as many curved lines as straight lines, and a vast percentage of curves are compound and not true arcs of circles. Since it is obviously impractical to use a compass and bow compass every time we come across a curve of this kind, we resort to an instrument known as the French curve.

The draftsman usually draws compound curves in pencil by marking a series of points on the curve and connecting them lightly with a thin pencil line. When this operation is finished, the French curve is "fitted" to the pencil curve, as shown in the curve at the upper right-hand corner of the opposite page. When the correct "fit" is obtained, the curve is inked in with the ruling pen. The other two large illustrations on the page show this same method of "fitting" the French curve to the required pencil curve or series of points.

There are many different kinds of French curves, some of which are shown inside the box page 31. They all require practice and skill in executing, so that it is suggested that, right now, you plot a number of points on your paper and practice using your French curve to connect these points in a continuous curve, first with your pencil and then with your ruling pen. Remember that the same rule applies to the French curve as applies to the T-square and tringles: DON'T move the curve while the line is wet, and DON'T slope the pen toward or away from the curve. Be particularly careful at the various connecting points where you change from one curve to another.

If you can't find a perfect fit for a curve, turn the French curve over and try again. The typical French curve shown outside the box will fit almost any curve you can plot. It is just a question of trial and error before you get it right.

If you have a symmetrical curve like an ellipse or a parabola, it is well to make a light pencil mark on your French curve between the two ends of a curve that fits. As the French curve is transparent, you will see these two marks when you turn the curve over and apply it to the other half of your symmetrical curve. This is particularly true for the ellipse, which is a very important curve because all circles, when viewed at a slant, become ellipses.

The Ellipse

Take an ordinary drinking glass and look directly at it from above. The edge will appear to be a circle. Now, if you hold the glass off a little way and view it on the slant, slightly below the eye level, the top edge becomes an ellipse. This is true of any cylinder; the ellipse varies from a circle when viewed from the top, to a straight line when viewed exactly at the eye level. This is demonstrated in Figure 12, page 30.

The true ellipse is very difficult to draw correctly. The only easy method of drawing perfectly smooth inked-in ellipses is with the aid of the ellipsograph, a very expensive instrument which is not manufactured at the present time. The most practical method of drawing an ellipse is the two-circle, French curve method shown in Figure 13a. Suppose you are required to draw an ellipse with a major axis of 3 inches and a minor axis of 1 inch. How would you go about doing it?

Draw a circle whose diameter is 1 inch, and, with the same center, draw another circle whose diameter is 3 inches. Now draw any lines through the common center of these two circles. You may draw as many as you wish, but the number shown here will do. These straight lines intersect the two circles. Where they cut the small circle, draw horizontal lines; where they cut the large circle, draw vertical lines. Where the horizontal and vertical lines intersect, make tiny pencil crosses, for these points are on the required ellipse. Now, very lightly, draw the curve in pencil, connecting all these cross marks, as shown in Figure 13a. You will have a rough pencil sketch of the required ellipse; it is now up to you to take your French curve and very carefully ink in this penciled ellipse. This will not be easy at first, but after a great deal of practice, you should be able to do it fairly well. Figure 13b shows the French curve being applied to the pencil sketch of the ellipse; Figure 13c shows the finished inked-in ellipse whose major axis is 3 inches and whose minor axis is 1 inch.

The method described will enable you to draw any ellipse. All you need to do is to draw two circles on a common center, the small circle with a diameter equal to the minor axis of the required ellipse and the large circle with a diameter equal to the major axis of the required ellipse. Then draw lines through the center; where these lines cut the small circle, draw horizontal lines; where they cut the large circle draw vertical lines. The intersection points of these lines will always be on the required ellipse.

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