Engineering H191 - Drafting / CAD Gateway Engineering Education Coalition Lect 21P. 1Autumn Quarter Review of Fits and Tolerances AutoCAD 3D Multiview Lecture 21

Engineering H191 - Drafting / CAD Gateway Engineering Education Coalition Lect 21P. 2Autumn Quarter 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.

Engineering H191 - Drafting / CAD Gateway Engineering Education Coalition Lect 21P. 3Autumn Quarter Direct limits and tolerance values Can be: Limits: Upper limit – 3.53 Lower limit – 3.49 Unilateral – vary in only one direction X +.0X - 0 Bilateral – vary larger or smaller (may or may not be same amount) , /

Engineering H191 - Drafting / CAD Gateway Engineering Education Coalition Lect 21P. 4Autumn Quarter 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)

Engineering H191 - Drafting / CAD Gateway Engineering Education Coalition Lect 21P. 5Autumn Quarter 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)

Engineering H191 - Drafting / CAD Gateway Engineering Education Coalition Lect 21P. 6Autumn Quarter Review – Fitting Two Parts Part A Tolerance of A Part B Tolerance of BTolerance: Clearance or Interference

Engineering H191 - Drafting / CAD Gateway Engineering Education Coalition Lect 21P. 7Autumn Quarter Review – Shaft and Hole Fits ClearanceInterference CLEARANCE FIT Allowance = +.003

Engineering H191 - Drafting / CAD Gateway Engineering Education Coalition Lect 21P. 8Autumn Quarter Review – Shaft and Hole Fits Transition CLEARANCE FIT +.003

Engineering H191 - Drafting / CAD Gateway Engineering Education Coalition Lect 21P. 9Autumn Quarter 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)

Engineering H191 - Drafting / CAD Gateway Engineering Education Coalition Lect 21P. 10Autumn Quarter Review – Basic Hole System Clearance = Hole – Shaft Cmax = Hmax – Smin Cmin = Hmin – Smax Both Cmax and Cmin > Clearance fit Both Cmax and Cmin < Interference fit Cmax > 0 and Cmin < Transition fit Allowance = Hmin - Smax (i.e., Cmin) GOOD TO KNOW

Engineering H191 - Drafting / CAD Gateway Engineering Education Coalition Lect 21P. 11Autumn Quarter Review – Basic Hole System System Tolerance = C max - C min –Sometimes called Clearance Tolerance Also, System Tolerance = Σ T i So, System Tolerance, or T s, can be written as: T s = C max - C min = Σ T i Thus, you always have a check value

Engineering H191 - Drafting / CAD Gateway Engineering Education Coalition Lect 21P. 12Autumn Quarter 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

Engineering H191 - Drafting / CAD Gateway Engineering Education Coalition Lect 21P. 13Autumn Quarter Multiview Layout of V-Block What views would be necessary to describe this part? What Dimensions will you need in these views?

Engineering H191 - Drafting / CAD Gateway Engineering Education Coalition Lect 21P. 14Autumn Quarter Auxiliary Views 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

Engineering H191 - Drafting / CAD Gateway Engineering Education Coalition Lect 21P. 15Autumn Quarter 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.

Engineering H191 - Drafting / CAD Gateway Engineering Education Coalition Lect 21P. 16Autumn Quarter 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

Engineering H191 - Drafting / CAD Gateway Engineering Education Coalition Lect 21P. 17Autumn Quarter 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