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# 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. How Would You Describe This?. Describe this using only words How effective is it?. Three Basic Types of Technical Drawings. Freehand sketches

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## Basics of Mechanical Drawing and Dimensioning

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1. Basics of Mechanical Drawing and Dimensioning ChE 126 Borrowed mostly from the Fundamentals of Engineering Honors program at Ohio State

2. How Would You Describe This? • Describe this using only words • How effective is it?

3. Three Basic Types of Technical Drawings • Freehand sketches • Instrument drawings • Computer drawings and models

4. Introduction to Projections • Present 3-D objects with 2-D media • Two Basic Categories OrthographicPictorial

5. Orthographic Projection

6. Defining the SixPrincipal ViewsorOrthographic Views

7. 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

8. For Example: 1. Visible 2. Hidden 3. Center

9. Use very light lines for drawing in the construction lines Step 1 – Lightly Block Three Views

10. Step 2 – Lightly Block Major Features • Holes • Arcs • Cutouts Use very light lines for drawing in the construction lines

11. Step 3 – Add Final Lines Use very light lines for drawing in the construction lines

12. Completed Sketch

13. 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

14. Units of Measure Angle Dimensions • Length • English: Inches, unless otherwise stated • Up to 72" • Feet and inches over 72" • SI: millimeter, mm • Angle • degrees, minutes, seconds

15. Dimensioning Basic Shapes – Assumptions • Perpendicularity • Symmetry

16. Dimensioning Basic Shapes • Rectangular Prism

17. ALWAYS give DIAMETER " " for full circles (360 degrees) and RADIUS "R" for arcs (less than 360 degrees) Dimensioning Shows: A) Size B) Location and Orientation

18. General Guidelines: Clarity is the Goal • Dimension Outside of View Avoid Good Practice

19. 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

20. Practice Problem How many Dimensions are needed?

21. Practice Problem How many Dimensions are needed? Answer: 8

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