Instrument Drawing and
Lettering Techniques
Instrument Drawing
Instrument Drawing
Objectives in Drawing
1.
Accuracy
2.
Speed
3.
Legibility
4.
Neatness
Typical Drawing Equipment
Instrument Drawing
Drawing Boards
The left edge and right edge of a
drawing board has a true straight
edge.
For right-handed people, the lefthand edge of the board is called the
working edge because the T-square
head slides against it.
For left-handed people, the righthand 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
CONSTRUCTION LINES
LEAD GRADE
3H, 4H, 6H
LINE WEIGHT
THIN, LIGHT
VISIBLE OBJECT LINES
H, F, HB
THICK, DARK
HIDDEN LINES
2H, H
THIN, DARK
CENTER LINES
2H, H
THIN, DARK
DIMENSION LINES
2H, H
THIN, DARK
EXTENSION LINES
2H, H
THIN, DARK
LEADER LINES
2H, H
THIN, DARK
H, F, HB
THICK, DARK
2H, H
THIN, DARK
H, F, HB
THIN, DARK
CUTTING PLANE LINES
PHANTOM LINES
LETTERING
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, and
architects’ 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 the
center 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.
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Lettering Technique
Lettering Techniques
Most engineering lettering is single-stroke
Gothic font. Lettering is drawn freehand and
are drawn within light horizontal guidelines.
Typically lettering is 1/8” high.
All lettering uses upper case letters. Lower
case letters are rarely used in technical
drawings.
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 to right, vertical
strokes are drawn from top to bottom, and
curved strokes are drawn downward.
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Lettering Technique
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