# Freehand Sketching - CAS

Standard Practice for Engineering Drawings Introduction to Mechanical Engineering Fall 2004 Created by: P.M. Larochelle Standard Sheets For layout designations, title blocks, revision blocks, and list of materials blocks see the

front inside cover of the text. Sheet size selection: For simple parts use small sheets For complex parts use large sheets Standard Sheets ANSI (US) (in) ISO (International)

(mm) A (8.5x11.0) A4 (210x297) B (11.0x17.0) A3 (297x420) C (17.0x22.0) A2 (420x594)

D (22.0x34.0) A1 (594x841) E (34.0x44.0) A0 (841x1189) Title Blocks Title Blocks record important info regarding

the drawing: Part name & number Names of the persons that: created, modified, and approved the drawing Dates that the drawing was created & revised Company Name

The scale of the drawing Etc. Title Blocks Scale The scale of the drawing is the ratio of the size of the object as drawn to the actual size. The scale you chose depends upon both the size of the object and the sheet size. When practical it is always preferable to

show parts and assemblies at full scale (I.e. actual size). Scale Scales are denoted by two numbers separated by a colon e.g. 1:10 On the left is the length on the drawing On the right is the actual length on the object

Always use integer scales Use 3:2 instead of 1.5:1 Scale Some

scales can be denoted by text 1:1 = FULL SCALE = FULL SIZE 1:2 = HALF SCALE = HALF SIZE 2:1 = DOUBLE = 2x Standard Scales ANSI (US) ISO (International) 1:1

1:1 1:2 1:2 1:4 1:5 1:8

1:10 1:10 1:20 Geometry A working knowledge of the fundamental principles and terminology of geometry is essential to create engineering drawings.

We will now review the basic concepts and geometric elements commonly encountered in engineering drawing. Points A point represents a location. It has zero dimensions; no length, width, or depth. A point is always defined by the intersection of two line segments- never by a dot.

Lines Euclid defined a line as that which has length without breadth. In Euclids time and for many hundreds of years thereafter any element- straight or curved that had no breadth was called a line (e.g. french curves, splines, etc.). Today, we define a line as being straight. A line represents a point and a direction. It has one dimension- length; it has no width or depth.

Lines A line has infinite length whereas a line segment is a line of finite length. In technical drawing we are always concerned with line segments. Therefore we abbreviate the term line segment to line. The term line in technical drawing always refers to a line segment. Lines Parallel

lines are pairs of lines that share the same direction but different points. Perpendicular lines are pairs of lines that share the same point but have orthogonal directions. In sketches you may denote two perpendicular lines with a box at their intersection- but never in drawings. Angles

An angle is formed by two intersecting lines. The common unit of measure for angles is the degree. There are 360 degrees in a full circle, 60 minutes in a degree, and 60 seconds in a minute. Example: 37o2610 is read as 37 degrees, 26 minutes, and 10 seconds. Alternatively, angles can be denoted by decimal degrees. Example 37.43611 (degrees).

Angles Supplementary angles sum to 180 (degrees). Complementary angles sum to 90 (degrees). An acute angle measures less than 90 (degrees). An obtuse angle measures more than 90 (degrees). Triangles A

triangle is a planar figure bounded by three line segments. The sum of the interior angles in a triangle is 180 (degrees). Polygons A polygon is any planar figure bounded by

straight lines- a triangle is a 3-sided polygon. If the polygon has equal angles and sides then it is a regular polygon. Circles A circle is a planar figure formed by the set of all points equidistant from a given point. The circumference is the distance around the circle. The radius is the distance from the points on the circle to the given point.

Solids Three-dimensional solids bounded by plane surfaces are called polyhedra. The plane surfaces that define a polyhedra are called faces. If the faces are regular polygons then the solid is called a regular polyhedra. Solids

References Chapters 3&4 of Modern Graphics Communication by Giesecke, Mitchell, Spencer, Hill, Dygdon, Novak, and Lockhard, 3rd edition. Prentice-Hall, 2004. Technical Drawing by Giesecke, Mitchell, Spencer, Hill, Dygdon, and Novak, 9th edition. Macmillan, 1991.

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