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Basics of Mechanical Drawing and Dimensioning. ChE 126 Borrowed mostly from the Fundamentals of Engineering Honors program at Ohio State. How Would You Describe This?. Describe this using only words How effective is it?. Three Basic Types of Technical Drawings. Freehand sketches - PowerPoint PPT Presentation
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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