Basics of Mechanical Drawing and Dimensioning
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Transcript of Basics of Mechanical Drawing and Dimensioning
Basics of Mechanical Drawing and Dimensioning
ChE 126
Borrowed mostly from the Fundamentals of Engineering Honors program at Ohio State
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How Would You Describe This?
• Describe this using only words• How effective is it?
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• Freehand sketches
• Instrument drawings
• Computer drawings and models
Three Basic Types of Technical Drawings
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Introduction to Projections
• Present 3-D objects with 2-D media• Two Basic Categories
Orthographic Pictorial
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Orthographic Projection
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Defining the SixPrincipal Views
orOrthographic
Views
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• Hidden Lines – represent features that cannot be seen in the current view
• Centerlines – represent symmetry and mark the center of circles, the axes of cylinders, and the axes of symmetrical parts, such as bolts
Hidden and Center Lines in Orthographic Projections
• Object Lines – represent visible features for an object
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For Example:
1. Visible
2. Hidden3. Center
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Step 1 – Lightly Block Three Views
Use very light lines for drawing in
the construction
lines
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Step 2 – Lightly Block Major Features
Use very light lines for
drawing in the construction
lines
• Holes• Arcs• Cutouts
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Step 3 – Add Final Lines
Use very light lines for drawing in
the construction
lines
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Completed Sketch
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Dimensioning
• Orthographic and isometric views define the shape and general features of the object
• Dimensioning adds information that specifies
– Size of the object
– Location of features (e.g. holes)
– Characteristics of features (e.g. depth and diameter of hole)
• Dimensions also communicate the tolerance (or accuracy) required
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Units of Measure
• Length– English: Inches, unless
otherwise stated• Up to 72"• Feet and inches over 72"
– SI: millimeter, mm
• Angle– degrees, minutes, seconds
Angle Dimensions
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Dimensioning Basic Shapes – Assumptions
• Perpendicularity
• Symmetry
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Dimensioning Basic Shapes
• Rectangular Prism
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Dimensioning Shows:
ALWAYS give DIAMETER " " for full circles (360 degrees) and RADIUS "R" for arcs (less than 360
degrees)
A) Size B) Location and Orientation
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General Guidelines: Clarity is the Goal
• Dimension Outside of View
Avoid Good Practice
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General Dimensioning Guidelines
• Start with basic outside dimensions of the object– Height– Width– Depth
• Add dimension for location and size of removed features
• Add general and specific notes – such as tolerances
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Practice Problem
How many Dimensionsare needed?
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Practice Problem
How many Dimensionsare needed?
Answer: 8