第1章几何作图

Example: Drawing of slope ( 1∶8, upon point 0 5mm left 100mm).
过O点左100mm、上5 mm之点作斜度为 1∶8的斜线。
1∶8
5 10
0
80
100
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30 10
H d
Slope and taper 斜度和锥度
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2）The procedure is as follows 加深描粗步骤 ①First thick lines and then thin lines: One should first draw continuous thick lines, then draw dashed thin lines, long dashed dotted thin lines and continuous thin lines.
2) Given the distance across corners, draw a regular polygon (n = 7).
已知其外接圆直径,作正多边形（n =7）。
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Slope and taper 斜度和锥度
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Hale Waihona Puke 1∶ n1.Slope 斜度
H
slope (斜度)= tanα= H / L
在A4图纸上,按2:1 的比例画出下面图形,粗实线宽度 为0.8mm，尺寸数字为3.5号。 （画图方法）
Title block (标题栏)
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Equilateral polygon 正多边形
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1) Construct regular hexagon (DIA 40mm=A/C of HEX).
标注时要注意符号斜线方向与锥度方向一致。
Example: Drawing of taper 1∶7 ( H = 30 mm, = 40 mm ).
已知 H = 30 mm, = 40 mm, 求作锥度为 1∶7的图形。
1∶7
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40 70
Arc connection 圆弧连接
(1)
画法二 (2)
60°
相切
Step off the radius round it to give six equally spaced points,Join these points to form the hexagon.
以外接圆半径R 等分圆周为6 点,连
接各点即得正六边形。
Draw tangents to this circle with a 60° set square to produce the hexagon. 画出内接圆,用60°三角板画正六边形
L
The slope symbol (符号): 30 1∶n
When dimensioning, the oblique direction of the slope symbol should be in accordance with the actual slope direction.
(标注时要注意符号斜线方向与斜度方向一致)
accurate, clear and clean.
图线细淡、准确、清晰，图面整洁。
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Techniques for drawing 2D objects 平面图形的画法
（3） Finalizing the drawing 加深描粗
1） Before producing the final drawing, one should check the sketches carefully, correct all mistakes, and erase all unnecessary curve segments. 加深描粗前，要检查底稿，修正错误，擦去多余图线。
Equilateral polygon 正多边形
2
1. Regular hexagons 正六边形的画法
1) Construct regular hexagon (DIA 40mm=A/C of HEX).
作正六边形(其外接圆直径d 为40 mm=正六边形对角距)。
2) Construct two regular hexagons (DIA 40mm=A/C or A/F of HEX
Geo几metr何ic Co作nstr图uction
Equilateral polygon
正多边形
Slope and taper
斜度和锥度
Arc connection
圆弧连接
Techniques for drawing 2D objects 平面图形的画法
Exercise
练习题
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Example: 1. Acute angle 锐角 2.Obtuse angle 钝角
3.Right angle 直角
2. Arc connection between two pieces of arcs. 用圆弧连接两个已知圆弧。
Example: 1.Externally 外切
2.Internally 内切
draw all known curve segments, then intermediate segments, and finally draw connection segments.
画作图基准线确定图形位置,依次画出已知线段和连接线段。
2）Requirements 要求 Use extra thin lines and the sketches should be
作两个正六边形(其外/内接圆直径d 为40 mm=正六边形对角/边距)。
2. Equilateral polygon 正n 边形的画法
1) Given the distance across corners, draw a positive pentagon (n = 5).
已知其外接圆直径,作正五边形（n =5）。
2) Define the scale, select the size of drawing sheet, and fix the drawing sheet on the drawing board.
确定比例，选定图幅，固定图纸。
3) Draw the border lines and produce the title box.
5
The so-called arc connection is often used for smooth connection between lines and circles using arcs.
所谓圆弧连接，是指由一圆弧光滑地连接相邻两线段（或圆弧）的作图方法。
Construct principle: The key in tangency principle is to find the center of the arc and the tangent position of the corresponding lines, line and arc, and arcs respectively.
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Equilateral polygon 正多边形
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1) Given the distance across corners, draw a positive pentagon (n = 5).
同类图线粗细浓淡一致, 连接光滑, 字体工整, 图面整洁。
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Exercise 练习题
Mark the following drawing on A4 sheet , scale 2:1， continues thick line 0.8mm，dimension size 3.5.
General drawing procedures 绘图的一般步骤 （1）Preparation 准备工作
1) Analysis dimensions and curve segments and plan for the drawing procedures.
分析图形的线段及分析尺寸，拟定作图步骤。
3. Arc connection between one line and another piece of arc. 用圆弧连接已知直线和已知圆弧。
Example:
1.Externally 外切
2. Internally 内切
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7
Techniques for drawing 2D objects 平面图形的画法
圆弧与圆弧连接(外切)
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O内
Internal arc connection between two pieces of arcs
圆弧与圆弧连接(内切)
Arc connection 圆弧连接
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There are three cases, i.e. 圆弧连接有三种基本形式
1. Arc connection between two lines. 用圆弧连接两条已知直线。
画出图框和标题栏。
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Techniques for drawing 2D objects 平面图形的画法
（2） Rough sketches 绘制底稿
1）Procedure for rough sketches 画底稿步骤 First draw datum lines for drawing positioning, then
作正六边形, (其外接圆直径d为40mm=正六边形对角距)
Steps 作图步骤：