Pencil

The pencils are used for preparing the drawings on the drawing sheet, to draw different lines, shapes, symbols and to write texts in engineering drawing. The accuracy and the appearance of the drawing depend upon the quality of pencil used. Different grades of pencils are available depending upon the hardness of the lid. Pencils of various grades can be easily recognised by the letters marked on the body of the pencil. The pencils are generally graded as H, F, B and HB. H represents hardness; F represents Firm, B represents Softness and HB represents intermediate between hard and soft. The general designation of a pencil is associated with alpha-numeric symbols such as 2H, 3H, HB, B, 2B, 3B, etc. Fig.1 shows various grades of pencils. Drawing pencils are graded as 7B, 6B,…, HB, H, 2H, . . . in the increasing order of their hardness and decreasing order of their blackness. Generally, drawings are made with 2H pencils and finished with H or HB pencils.

Fig. 1: Pencil Grades

Pencils of Different Grades

Pencils are graded according to the hardness or softness of the lead. Selection of proper grade pencil or lead is important for quality drawing. One has to be careful in selecting a lead because very hard lead might penetrate the drawing, on the other hand, soft lead may smear. Quality and type of drawing paper is an important factor in selecting lead. One other importance consideration is the importance of line to be drawn. Inferior lines (like border lines, guide lines, construction lines and any other auxiliary lines needed to be erased later) are drawn using harder pencil. Comparatively softer grade pencil is used for drawing superior items (like object line, texts, symbols etc.).

Table 1 Pencil Usage Guideline for Different Line Types

Sl. No.	Task	Lead
1	Construction Lines	3H, 2H
2	Guide Lines	3H, 2H
3	Lettering	H, F, HB
4	Dimension Lines	2H, H
5	Leader Line	2H, H
6	Hidden Lines	2H, H
7	Cross Hatching Lines	2H, H
8	Centre Lines	2H, H
9	Phantom Lines	2H, H
10	Stitch Lines	2H, H
11	Long Break Lines	2H, H
12	Visible Lines	H, F, HB
13	Cutting Plane Lines	H, F, HB
14	Extension Lines	2H, H
15	Freehand Break Lines	H, F, HB

In drawing, standard pencils (lead encased in wood) and semi-automatic pencils are made use. Pencil leads are made of graphite with kaoline (clay) of varying proportion to get the desired grades. More the kaoline higher the hardness. The hardest pencil is 9H grade and softest pencil is 7B grade. Softer lead pencils are used to produce thicker and darker line work, but they wear out quickly. Medium grade of H, 2H are used for general line work as well as for lettering. Harder grade leads produce lighter and thinner lines. Most construction line work is done with 4H, 5H and 6H pencil leads, producing thin but also sufficiently dark by exerting pressure. Depending upon the individual's touch and the style of writing, the right pencil may be selected. In general H, HB and 2H are used.

General Selection

• HB- For freehand works, sketching.
• H- For outlines, visible lines, finishing, dimensioning, lettering, arrows etc.
• 2H - For drawing construction lines, dimensions lines, section lines, and center lines.
• 3H, 4H- For drawing minute details
• B- For shading

Great care should be taken in mending the pencil and sharpening the lead, as the uniformity in thickness of lines depends largely on this. To prepare the pencil lead for drawing work, the wood around the lead from the end, other than that on which the grade is marked, is removed with a pen-knife, leaving about 10 mm of lead projecting out. The conical point is used in sketch work and for lettering etc. The lead may be sharpened into different forms.

i) Conical point

ii) Chisel edge

iii) Bevel edge

iv) Cylindrical edge

With the chisel edge, long thin lines of uniform thickness can be easily drawn and hence, it is suitable for drawing work. The chisel edge is prepared by rubbing the lead on a sand-paper block, making it flat, first on one side and then on the other by turning the pencil through a half circle. For making the conical end the pencil should be rotated between the thumb and fingers, while rubbing the lead. The pencil lead should occasionally be rubbed on the sand-paper block (while doing the drawing work) to maintain the sharpness of the chisel edge or the pointed end. Instead of wooden pencils, Mechanical clutch pencils with a different lead size (lead dia 0.3, 0.5, 0.7 or 0.9 mm) and grade like H, 2H, HB etc., are also available. They are easy to handle as there is no reduction of holding length pencil leads can be replaced, as per required grade of hardness. They produce lines of uniform width without sharpening.

For any drawing on drawing paper or tracing paper, lines should be black, particularly drawings which are to be reproduced. For this purpose, the pencil chosen must be soft enough to produce jet black lines as well as hard enough not to smudge easily. The point should not crumble under normal working pressure. The pencils should not be hard and cut grooves on the paper while drawing with normal pressure, Pencils H, 2H or 3H depending upon the paper (quality) and weather conditions are selected. In summer the pencil leads become softer due to rise in temperature, so slightly harder pencils can be made use of softer grade pencils are used on smooth surfaces for lettering and arrow head. During rainy season or when humidity is more, the drawing paper expands and wrinkles form, pencil leads become harder. So softer pencils are to be used. For better line work, i.e., dense black lines, prefer paper which is not having too much teeth (roughness).

Pencils used for drawing are always hexagonal in cross sections as they do not roll easily even when they are placed on slope surfaces. Its cross section helps in rotating the pencil, while drawing lines, to give uniform line thickness.