Pp Chapter 3

7/30/2019 Pp Chapter 3

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Instrument Drawing and

Lettering Techniques

Instrument Drawing



Instrument Drawing

Typical Drawing Equipment

Objectives in Drawing

1. Accuracy

2. Speed

3. Legibility

4. Neatness



Instrument Drawing

Drawing Boards

The left edge and right edge of a

drawing board has a true straight

edge.

For right-handed people, the left-

hand edge of the board is called the

working edge because the T-squarehead slides against it.

For left-handed people, the right-

hand edge of the board is called the

working edge because the T-square

head slides against it.

T-Squares

The T-square is made of a long strip

called the blade, fastened at right

angles to a shorter piece called the

head.



Instrument Drawing

The drawing paper should be placed

close to the working edge of the

board to reduce any error resulting

from the bending of the blade of the

T-square.

The paper should also be placed

close enough to the upper edge of

the board to permit space at the

bottom of the sheet for using the

T-square.

Drafting tape is used to fasten the

drawing paper to the drawing board.



Instrument Drawing

Drawing Pencils

High-quality drawing pencils should be used in technical drawing, never ordinary writing pencils.

Many makes of mechanical pencils are available together with refill leads in all grades. Choose a

mechanical pencil that feels comfortable in your hand.



Instrument Drawing

Drawing Leads

The first consideration in the selection of a grade of lead is the type of line work required. For

light construction lines and guide lines for lettering use a hard lead. For all other line work, the

lines should be BLACK. The lead chosen should be soft enough to produce jet black lines but

hard enough not to smudge.

HARD MEDIUM SOFT

9H 8H 7H 6H 5H 4H 3H 2H H F HB B 2B 3B 4B 5B 6B 7B

Hard leads are used where extreme

accuracy is required. Generally

these leads are used for construction

lines.

Medium leads are used for general

purpose line work in technical

drawing.

Soft leads are used for various kinds

of art work. These leads are too soft

to be useful in mechanical drafting.



Instrument Drawing

Drawing Lead Applications

TASK LEAD GRADE LINE WEIGHT

CONSTRUCTION LINES 3H, 4H, 6H THIN, LIGHT

VISIBLE OBJECT LINES H, F, HB THICK, DARK

HIDDEN LINES 2H, H THIN, DARK

CENTER LINES 2H, H THIN, DARKDIMENSION LINES 2H, H THIN, DARK

EXTENSION LINES 2H, H THIN, DARK

LEADER LINES 2H, H THIN, DARK

CUTTING PLANE LINES H, F, HB THICK, DARK

PHANTOM LINES 2H, H THIN, DARK

LETTERING H, F, HB THIN, DARK



Instrument Drawing

Drawing Horizontal and Vertical Lines

To draw a horizontal line, press the head of the

T-square against the working edge of the board

with your left hand. Lean the pencil in the

direction of the line at an angle of approximately

60º and draw the line from left to right. While

drawing the line, rotate the pencil to distribute

the wear uniformly on the lead to maintain a

symmetrical point.

To draw a vertical line, press the head of the T-square

against the working edge of the board with your left hand

and place a triangle against the blade of the T-square.Lean the pencil in the direction of the line at an angle of

approximately 60º and draw the line upward, rotating the

pencil to distribute the wear uniformly on the lead to

maintain a symmetrical point.



Instrument Drawing

Triangles

Most inclined lines are drawn at standard

angles using the 45º x 45º triangle and

the 30º x 60º triangle.

In addition to drawing angles of 90º, 45º,

30º, and 60º, triangles can be combined

to draw angles of 15º increments.



Instrument Drawing

Scales

Scales are instruments used in making

technical drawings full size or at a given

reduction or enlargement.

Types of scales include metric scales,

engineers’ scales, decimal scales,

mechanical engineers’ scales, andarchitects’ scales.

Scales are usually made of plastic or

boxwood and are either triangular of flat in

shape.



Instrument Drawing

Giant Bow Sets

Giant bow sets contain various combinations

of instruments.

Giant Bow Compass

The giant (large) bow compass has a center

wheel and can be adjusted simply by opening or

closing the legs of the compass while turning thecenter wheel.



Instrument Drawing

Using a Giant Bow Compass

1. Set off the required radius on one of the center

lines.

2. Place the needle point at the exact intersection of

the center lines.

3. Adjust the compass to the required radius

4. Lean the compass in the direction that you are

going to draw the circle. Draw the circle in a

clockwise direction while rotating the handle

between the thumb and forefinger.



Instrument Drawing

Sharpening the compass lead

A properly sharpened compass point is formed by

rubbing the lead on the sandpaper pad.

A properly sharpened

compass point consists of a

single elliptical face.

A properly adjusted compass

The needlepoint extends about

halfway into the paper when the lead

touches the paper.



Instrument Drawing

Pencil Drawing Techniques

A quality drawing is characterized by crisp black line work and lettering.

All finished pencil lines should be very dark. Construction lines should be made very light so

that they need not be erased when the drawing is completed.

Contrast in pencil lines should vary in the widths of the lines. Visible object lines should

contrast strongly with the thin lines of the drawing.

.



Lettering Technique

Lettering Techniques

Most engineering lettering is single-stroke

Gothic font. Lettering is drawn freehand

and are drawn within light horizontal

guidelines.

All lettering uses upper case letters. Lower

case letters are rarely used in technicaldrawings.

There are three aspects of good lettering:

proportions and forms of the letters,

composition and spacing, and practice.

There are six fundamental drawing strokes

and their directions in basic lettering.

Horizontal strokes are drawn from left toright, vertical strokes are drawn from top to

bottom, and curved strokes are drawn

downward.

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