Review of Fits and Tolerances AutoCAD 3D Multiview

1. Review of Fits and TolerancesAutoCAD 3D Multiview Lecture 21 Autumn Quarter

2. Review – Definition of Tolerance • Tolerance is the total amount a dimension may vary. It is the difference between the maximum and minimum limits. • There is no such thing as an "exact size". • Tolerance is key to interchangeable parts. Autumn Quarter

3. Direct limits and tolerance values Can be: Limits: Upper limit – 3.53 Lower limit – 3.49 Unilateral – vary in only one direction 3.49 0 -.0X +.0X - 0 Bilateral – vary larger or smaller (may or may not be same amount) 3.50 +.05 -.01, +.10 -.20 +/- 0.05 +.04 0 +.03 -.01 Autumn Quarter

4. Important Terms – Single Part • Nominal Size – general size (1/2”) • Basic Size – theoretical size used as starting point (.500”) • Actual Size – measured (.501”) • Limits – maximum and minimum sizes shown by tolerances • Tolerance – total allowable variance in dimensions (upper – lower limit) Autumn Quarter

5. Important Terms – Multiple Parts • Allowance – the minimum clearance or maximum interference between parts • Fit – degree of tightness between two parts • Clearance Fit – tolerance of mating parts always leave a space • Interference Fit – tolerance of mating parts always interfere • Transition Fit – sometimes interfere, sometimes clear • Tolerance – total allowable variance in dimensions (upper – lower limit) Autumn Quarter

6. Tolerance of B Tolerance: Clearance or Interference Part B Tolerance of A Part A Review – Fitting Two Parts Autumn Quarter

7. CLEARANCE FIT Allowance = + .003 Review – Shaft and Hole Fits Clearance Interference Autumn Quarter

8. CLEARANCE FIT+ .003 Review – Shaft and Hole Fits Transition Autumn Quarter

9. Standard Precision Fits: English Units • Running and sliding fits (RC) • Clearance locational fits (LC) • Transition locational fits (LT) • Interference locational fits (LN) • Force and shrink fits (FN) See Tables in the Appendix (pp. A11-A23) Autumn Quarter

10. Review – Basic Hole System • Clearance = Hole – Shaft • Cmax = Hmax – Smin • Cmin = Hmin – Smax Both Cmax and Cmin > 0 --- Clearance fit Both Cmax and Cmin < 0 --- Interference fit Cmax > 0 and Cmin < 0 --- Transition fit • Allowance = Hmin - Smax (i.e., Cmin) GOOD TO KNOW Autumn Quarter

11. Review – Basic Hole System • System Tolerance = Cmax - Cmin • Sometimes called Clearance Tolerance • Also, System Tolerance = Σ Ti • So, System Tolerance, or Ts, can be written as: Ts = Cmax - Cmin = Σ Ti • Thus, you always have a check value Autumn Quarter

12. Multiview Drawings From 3D Models • A major advantage of creating a 3D model of a part is that the separate views do not need to be created in 2D. • The views can be created in Paper Space from the 3D Model Autumn Quarter

13. What views would be necessary to describe this part? What Dimensions will you need in these views? Multiview Layout of V-Block Autumn Quarter

14. An Auxiliary view of this surface will be needed… would this be easy to draw in 2D? Once modeled in 3D, creating the view is quick and easy Auxiliary Views Autumn Quarter

15. Notes on Lesson 8 • Pay close attention to the use of the Properties button • This is a powerful tool that can be used to modify all objects created • Note the method shown for setting the scale and aligning the views. It is more complex than what we have done in the past, but a good method when dealing with many views. Autumn Quarter

16. Notes on Lesson 8 • Another command used in this lesson is ‘SOLPROF’ • This command creates a 2D profile from the 3D model – with options for showing hidden lines and object lines correctly. • Be sure to closely follow the steps to set the correct options Autumn Quarter

17. Assignments • Dwg 41 – TOL–3B – Fits & Tolerances • Calculate the missing tolerances for the given sets of parts. • Use the tables for preferred limits and fits for cylindrical parts. • Dwg 42 – AC3D Lesson 8 • Multiview Drawings From 3D Models Autumn Quarter