Part 26

In practice, the flat side of the drawing-pen is laid against the tee-square or ruler; the taper of the blade of the pen is sufficient to throw the point enough away from the edge to prevent blotting; the pen is drawn from left to right and from the bottom to the top of the board.

This is shown in fig. 237, intended to represent “short work” with the drawing-pen. The wrist is shown resting upon the blade of the square.

In a similar figure, 238, the position of the hand holding the pen indicates the best relative posture for inking long lines. In one of these illustrations the work is executed principally by the wrist--in the other by the arms and fingers working together.

The pen should be held with even pressure against the straight-edge or curve. If the pressure varies, the blades will spring and the width of the line will change. The blades should be of such length that both will bear equally upon the paper when the pen is inclined slightly, so as to bring the inner blade near the straight-edge; the angle of the pen should not be changed while drawing any line.

When the inking is finished, the whole drawing may be cleaned by rubbing it with bread which is not greasy or so fresh as to stick to the paper. If the paper is much soiled it may be necessary to use an eraser. A soft pencil eraser should be used and great care taken that the ink lines are not lightened and broken by it.

To avoid the necessity of using an eraser upon a finished drawing, instruments and paper must be kept free from dust and dirt. The triangles and T-square should be cleaned often, by rubbing them vigorously upon rough, clean paper.

Pounce is a powder used to prevent blotting in rewriting over erasures; it is held in a bag or small box with a perforated lid for convenience in sprinkling on paper; when used it should be distributed evenly with a piece of chamois, and the surplus or loose particles removed before applying the ink.

A drawing is made to be read, and the skill in inking, as in “free-hand” and in penciling, does not consist so much in the fineness of the lines as in their clearness.

Lettering Drawings.

Lettering is an important part of making drawings, the object aimed at being to identify any portion by reference letter or letters; thus in fig. 239 the line A C describes the line extending from

Any information which cannot be expressed in the drawing is always expressed by lettering, and it is desirable to confine the lettering of drawings to one or two standard alphabets that are plain and distinct, and the principles of which are easily acquired. These conditions are fulfilled in the Gothic fonts shown on page 173.

Both letters and figures must be carefully made and of uniform proportion; it is well to “lay out” these by regular measurement before permanently inking them. Letters should not be less than one-eighth of an inch in height and penciled carefully before inking.

On page 173 are printed two forms of numerals and letters of the alphabet; it is recommended that these be used both for practice in free-hand and for regular office work.

For easy reference, letters should not be crowded nor allowed to interfere with one another; they should be drawn neatly, avoiding all lines of the drawing; plain letters are always used on mechanical drawings, whether for title, scale, reference, etc.

Arrow-heads, figures and letters should be in black, and made with a writing pen. A pen with a ball point is preferable, giving an equal thickness of line, no matter in which direction the stroke is made.

Neat, well-lettered drawings go far towards establishing a high standing for the aspiring draughtsman. All lettering should be done free-hand, first with the pencil, sharpened to a fine round point, and afterwards written in ink. For this purpose common writing pens are best to be used; fig. 240 represents the several numbers of the approved Gillott’s pens adapted to this purpose.

In lettering, it is well, for a guide for size and location, to draw, with a round-pointed pencil, two horizontal lines just the height the letters are to be; the letters are also best made with careful use of the instruments, rather than free-hand.

In order to letter systematically, it is a good plan to start with the middle letter of the inscription and work in both directions; making too prominent letters should be avoided, plain and distinct letters being most desirable.

Finally, with an ordinary writing pen, trace over the penciling in ink; the pencil guide lines being erased after the letters are inked in completes the operation.

An important matter in connection with lettering a drawing is the location of the letters; these should be so placed as not to interfere with the lines of the drawing and should clearly point out the part intended to be described. When single letters are used, they should be inked in before the shade or section lines are drawn.

Fig. 241 is an example introduced to show the method of lettering a descriptive mechanical drawing.

The figure shows a “blow-off valve” of approved design drawn in section; the letters designate the several parts; the reading to accompany the lettering is as follows:

=A=--Inlet communicating with annular passage (C) to admit steam, which blows off scale and sediment from seat (E) before disc (L) comes in contact with same.

=B=--Plug to permit passage of rod to clean out blow-off pipe.

=C=--Annular steam passage around casing (D) and communicating with inlet (A).

=D=--Removable bronze casing, in which plug (L) fits snugly.

=E=--Removable bronze seat ring, which also holds casing (D) in place.

=J=--Slot in casing (D) arranged to discharge sheet of steam from C, which, blowing across seat (E), cleans off scale and sediment before contact with disc (L).