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