Transcript 工程制图 - sdust.edu.cn

CONTENTS
Introduction
Chapter1 Basic Knowledge of Engineering Drawing
Chapter2 Projection of Points, Lines and Planes
Chapter 3 Solids and Their Intersections
Chapter4 Views and Dimensions of Composite Solids
Chapter5 Axonometric Projection
Chapter6 Representation methods of part
Chapter7 Standard Parts and Commonly Used Parts
Chapter 8 Detail Drawing
Chapter 9 Assembly Drawings
Introduction
1. Subjects and features of this course
Engineering Drawing is an application oriented
subject that introduces the preparation, representation
and reading of engineering drawings.
Engineering Drawing is an important document in
industry for design, manufacture, utilization and
service, often called “ the common technical language
for engineers”.
2. Nature and tasks of this course
(1)To study the basic theory and applications of
orthographic projection and train students with
abilities in design and innovation.
(2)To train students with a balanced skill in hand
drawing, instrument drawing and computer assisted
drawing as well as the ability in reading mechanical
drawings.
(3) To train students with abilities in spatial and
logical thinking, visual imagination,
conceptualization, exploration and innovation.
3.Study Method and Test
(1) more observation, more thinking, more practice
(2) Evaluation: homework-10%, CG-10%，
final examination-80%
(3) exercises：text style, number, on time
Chapter1 Basic Knowledge of
Engineering Drawing
1.1 Related Provision in National Standards
1.2 Drawing Methods
1.3 Techniques for Drawing 2D Objects
1.4 Drawing Skill
1.1 Related Provisions in National
Standards
Engineering drawing is an important documentation used during the process of design and
manufacturing. For the sake of convenience in
communication, all drawings should comply with
the national standards. National standards are
abbreviated as “GB” with a code.
1.1.1 Standard drawing sheets with layout
（GB/T14689--1993）
1. Standard sheets
While producing the drawing, one should usually adopt
the Standard sheets illustrated follow table. If it is necessary, one may also extended sheets of larger size specified
in the Standard.
2. Layout of standard sheets
One must use solid lines to draw the border. There
are two layouts to follow, i.e., with or without space
for book binding.
Border
Border
Title box
Layout of standard sheets (without space for
book binding)
3. Title box
One must draw a title box on each drawing sheet. The
position of the title box should be located on the lower
right corner of the sheet.
1.1.2 Scale (GB/T14690-1993)
1. Definition
The ratio between the dimension on the drawing and
features of actual object is called the scale of the drawing.
For dimensioning, one should always mark the actual dimensions in matter the drawing is enlarged or scaled down.
2. Scale of drawings
1.1.3 Lettering (GB/T14691-1993)
In the drawing, lettering of characters or
numbers must follow the national standards.
1. General regulation
(1) The characters must be whole and clear. The distance between characters must be uniformly distributed,
standing in a line.
(2) The font for Chinese characters should be the “Fang
Song” and the standard simplified Chinese characters should be
used. The height of characters should not be less than 3.5mm and
the width should be2/3 h.
(3) The number of characters is the same as the height
of the characters, such as 1.8, 2.5, 3.5, 5, 7, 14, 20mm.
(4) The font for all characters can be in italic fontor normal/
straight font. The italic font character should be inclined towards
the right with an angel of 75°with respect to horizontal lines.
2. Examples
Chinese characters
Numbers
Letters
Examples
1.1.4 Line styles (GB/T17450—1998)
1. Line styles and their utilization
All line name, styles, line thicknesses and their
application are defined in national standard. There
are eight line styles. When producing the drawing,
the width of thick lines should be 0.18, 0.25, 0.35,
0.5, 0.7, 1.0, 1.4, or 2mm. There are two line
thicknesses, namely thick lines and thin lines. Their
Scale is 2:1.the width of thick lines is based on the
dimension and structure of the drawing.
2. Line styles
Continuous
thick line
b
Dashed
lines
Continuous
thin line
Continuous
thin irregular
line
Thin dashed
dotted line
Continuous thin
straight line
with intermittent zigzags
Thin long dashed
double dotted line
Thick dashed dotted
line
1/3b
1/3b
1/3b
1/3b
1/3b
1/3b
b
To indicate
visible outlines,
Run-out line
To indicate
hidden outlines,
Run-out line
For fictitious outlines, dimensions,
projection hatching and leader line ,etc
Part sectional boundary lines or to
terminate a part view, and for short
break line
Axis lines, summetrical
center lines, etc
To show a break on an
adjacent member to
which a component is
attached
To indicate adjacent parts
alternative and extreme position of
moving parts
To indicate a cutting plane for
sectional views
Run-out line
The intersection line of two surfaces is not clear due
to the fillets of castings. the intersection line is needed
in order to distinguish the various surfaces. The one we
have provided is called run-out line.
3. Further notes for drawing lines
(1) In the same drawing, one should use the same line width for
the same type lines. The length and the distance of dashed lines,
dashed dotted lines, thin long dashed double dotted lines should
also be the same respectively.
(2) The center line should be longer from 2 to 5 mm than the
drawing frame, the head line or end line should be long dot, but
no short dot. And the center of a circle is the intersection point of
long dots.
(3) When it is difficult to draw dot line or double dot line in small
drawing, it can be replaced by continuous thin line.
(4) When two thin dashed lines meet together, the line segments
should meet ( not space ). When a thin dashed line is an extension
of a continuous line, a little space should be kept at the
intersection position.
4. Example of drawing lines
A
D
B
A Visible edges
B Dimension line and
Extension line
B1 Hatching line
A
C Boundary between
view and section
D Hidden edges
E Center line
B1
C
E
C
F
F Imaginary line
1.1.5 Dimensioning
1. Basic rules
(1) The true size of the space part is based on the dimension marked
on the drawing and has nothing to do with the size of the drawing and
the accuracy of the drawing.
(2) There is no need to mark the unit of dimensions if it is “mm”.
One only needs to mark the dimensions if the units are not “mm”,
but some others.
(3) All dimensions marked in the drawing are
dimensions of the final part.
(4) Each dimension of the part should mark on the
drawing only once. It should also be marked on a
drawing that most clearly indicate on the drawing.
2. Dimension construction
Extension line
Dimension line The Dimension figure Arrow head
Extension line beyond2-3mm
(1) Extension line
An extension line is drawn with a continuous thin line and it illustrates the scope of the corresponding dimension. An Extension line
originates from a feature outline, an axis line, or a symmetrical center
line. And the outline, axis line and symmetrical center line can also
be used as extension line .
An Extension line originates
from a feature outline
Spacing between dimension
lines and outline should be
equal and about 6to8mm
An Extension line originates
from a symmetrical center line
(2) Dimension line
A dimension line must be drawn using thin solid line and cannot be replaced by existing lines in the drawing. It can not be in
coincidence with any existing lines or be drawn as extension of
any existing lines.
For linear dimension, the dimension line must be parallel to
line segment being dimensioned.
Right
Wrong
(3) Terminal of dimension line
45°
4b
h
b
Right
Wrong
(4) Dimension text
Dimension text should usually be marked above the dimension
line or in the breaking space of a dimension line.
Right
Wrong
3. Dimension symbols
(1) Linear dimensions
All Linear dimensions should usually be marked heading upwards for
horizontal dimensions, heading towards the left for vertical dimensions, or with an inclination heading upwards for general cases as
shown in (a) and (b).
(2) Angle
All dimension text should be marked with horizontal orientation.
Extension lines should follow the radial direction and the dimension
line should be an arc whose center coincides with the apex point of
the extension lines.
(3) Circle
If the dimension is for the diameter of a circle, one should add
the symbol “Φ” before the dimension figure. The dimension line
should go through the center of the circle.
(4) Arc
For arcs with radius, one should add the symbol “R” before the
dimension figure. The dimension line should meet the center of the
circle.
(5) Big arc
For arcs with large radius, one may draw dimension lines as shown
in the figures and then notes.
(6) Surface of sphere
One should add the symbol “S” before “Ф”or “R”. However, the
symbol “S” may be omitted. If it does not cause any misunderstanding.
(7) Baby size
In case of insufficient space, the arrowhead can be drawn outside the
dimension line or replaced with a small dot. Dimension text can also
be located outside the dimension line or marked with a leader dimension.
(8) The length of an arc
When dimensioning the length of an arc, the dimension line should
run parallel with the arc. The extension lines should run in parallel
with the mid partition radial axis. Dimension text should be placed
above the dimension line and a symbol “︵”should be placed above
the dimension figure.
(9) Square construction
Dimensions for square cross sections should be marked with
symbol “□”or in the form of 14×14.
(10) Half of the part or little larger
Dimension line should be extended beyond the symmetry center
line or broken boundary line. Only one arrowhead is required on the
corresponding side of extension line.
1.2 Drawing Methods
1.2.1 Drawing tool and their utilization
1. Drawing board:
A drawing board is used to fix drawing sheet and produce drawing
on the sheet. The surface of the board should be flat and smooth.
The left side is the lead side and should be straight for guiding
rulers.
2. T-square: A T-square can be directly used to draw horizontal
lines. It can be used to draw vertical lines in combination with a
triangle.
3. Triangle：A Triangle is often used in combination with a Tsquare to draw vertical lines, lines with an inclination angle of 15°,
30°, 45°, 60°or 75°with horizontal lines.
T-square
4. Pencil:
H or 2H— to draw thick lines.
HB or H— to write characters.
HB or B—to draw thick lines.
5. Compass: A compass is used to draw circles and arcs. The leg of the
compass with a step pin should be facing downward and the pencil tip
on the other leg should have similar height to the pin.
6. Divides: Divides are used for transferring distances and for equal
subdivision of lines and circles.
1.2.2 Geometric Construction
1. Equilateral polygon
T- square
T- square
Equilateral polygon
2. Slope and taper
Slope
The Slope is an inclination of one line with respect to another line
or the inclination of one plane with respect to another plane .
Slope=H/L=tanga=1:k
Slope symbol:
Example 1. Draw the follow view on the position
indicated with a scale 1:4.
Dimension of Slope
Taper
The Taper of a cone is defined as the ratio between the
diameter of the bottom circle and the height.
Taper =D/H=1:k
Taper =(D-d)/L1=1:k
Taper symbol:
Example 2. Draw the follow view on the position
indicated with a scale 1:1.
3. Tangency principle
Tangency principle is often used for smooth joining between
lines and circles using arcs.
Three elements of joining ：Center of the arc, Tangent, Radius.
Arc connection between two lines
R
m
Arc connection between two pieces of arcs
External arc
connection
Internal arc
connection
External arc connection between two pieces of arcs
R
Internal arc connection between two pieces of arcs
R
Arc connection between one line and another
piece of arcs
R
4. Drawing methods of ellipse
E
F
A
C
O4
O1
O3
O2
D
B
1.3 Techniques for Drawing 2D Objects
1.3.1 Analysis of known dimensions
Shape dimension: Shape dimension are used to
determine the size of individual elements of the 2D
objects.
Locate dimension: Locate dimension is used to
determine the relative position of individual elements
of the objects.
Datum: Dimension datum
indicates common starting
position of related dimensions.
①Symmetry line;
②Center of a circle;
③the long line.
1.3.2. Analysis of individual segments of the
2D objects.
1. Known segments: Known segments are those with all dimensions
for shape and position.
2. Intermediate segment: segments that have only shape dimensions
and incomplete positioning dimensions are
called Intermediate segment.
3. Connection segment: segments that have only shape dimensions but
without location dimensions are called
connection segment.
1.3.3 General drawing procedures
1. Analyze dimensions and curve segments.
2. Rough sketches
First draw datum lines for drawing positioning, then
draw all known curve segments, then intermediate segments, and finally draw connection segments.
3. Finalizing the drawing.
Before producing the final drawing, one should check
the sketches carefully, correct all mistakes, and erase all unnecessary curve segments.
Procedure for preparing rough sketches (use the
handle as an example)
Finalizing the drawing (use the handle as an example)
Example 3. Draw the follow view on the position
indicated with a scale 1:1.
1.4 Drawing Skill
1.4.1 General drawing procedures
1. Preparation
2. Analyze dimensions and curve segments.
3. Rough sketches
4. Finalizing the drawing.
5. Dimension, Check and fill in the title box
1.4.2 Rough sketches by free hand
The End