Dimensioning and Tolerancing

Dimensioning&Tolerancing : 

Ken Youssefi Mechanical & Aerospace Engineering Dept., SJSU 1 Dimensioning&Tolerancing

Dimensioning : 

Ken Youssefi Mechanical & Aerospace Engineering Dept., SJSU 2 Dimensioning Size dimensions 2D drawings (shop drawings) must show proper dimensions to fabricate parts

Dimensioning Terminology : 

Ken Youssefi Mechanical & Aerospace Engineering Dept., SJSU 3 Dimensioning Terminology 1.25

Slide 4: 

Ken Youssefi Mechanical & Aerospace Engineering Dept., SJSU 4 Pull down menu Dimension Style

Slide 5: 

Ken Youssefi Mechanical & Aerospace Engineering Dept., SJSU 5

Accuracy : 

Ken Youssefi Mechanical & Aerospace Engineering Dept., SJSU 6 Accuracy 1.25 indicates ± .01 variation is acceptable (1.24 to 1.26) Requires twice as much time to machine. Use fractional dimensions when accuracy is not important, 2 ¼ , 5 ½ ,….. Architectural dimensioning: use combination of feet and inches, 7’ – 3

Placement of Dimensions : 

Ken Youssefi Mechanical & Aerospace Engineering Dept., SJSU 7 Placement of Dimensions

Do’s & Don’t’s of Dimensioning : 

Ken Youssefi Mechanical & Aerospace Engineering Dept., SJSU 8 Do’s & Don’t’s of Dimensioning

Do’s & Don’t’s of Dimensioning : 

Ken Youssefi Mechanical & Aerospace Engineering Dept., SJSU 9 Do’s & Don’t’s of Dimensioning

Dimensioning : 

Ken Youssefi Mechanical & Aerospace Engineering Dept., SJSU 10 Dimensioning

Avoid Over-Dimensioning : 

Ken Youssefi Mechanical & Aerospace Engineering Dept., SJSU 11 Avoid Over-Dimensioning

Avoid Over-Dimensioning : 

Ken Youssefi Mechanical & Aerospace Engineering Dept., SJSU 12 Avoid Over-Dimensioning Θ = tan-1(12.7/7.1) = 60.8o

Basic Dimensioning Style : 

Ken Youssefi Mechanical & Aerospace Engineering Dept., SJSU 13 Basic Dimensioning Style Continue dimensioning

Tolerancing : 

Ken Youssefi Mechanical & Aerospace Engineering Dept., SJSU 14 Tolerancing Parts made by different companies have to be interchangeable. Mating parts have to fit precisely. Tolerancing is the technique of dimensioning parts within a desired range of variation. Why tolerancing?

Size Tolerancing : 

Ken Youssefi Mechanical & Aerospace Engineering Dept., SJSU 15 Size Tolerancing

Mating Parts : 

Ken Youssefi Mechanical & Aerospace Engineering Dept., SJSU 16 Mating Parts

Type of Fits for Mating Parts : 

Ken Youssefi Mechanical & Aerospace Engineering Dept., SJSU 17 Type of Fits for Mating Parts Clearance Fit – Results in a space between the mating parts. Interference Fit – Results in an interference between two parts (no space). It requires force to assemble parts (force fit). Transition Fit – May results in either interference or clearance fit.

Example – Clearance Fit : 

Ken Youssefi Mechanical & Aerospace Engineering Dept., SJSU 18 Example – Clearance Fit

ANSI Tables for Fits : 

Ken Youssefi Mechanical & Aerospace Engineering Dept., SJSU 19 ANSI Tables for Fits Clearance fits (running and sliding) – RC1 to RC9 0.75 +1.2 +0.0 -.8 -1.6 Class RC 4

ANSI Tables for Fits : 

Ken Youssefi Mechanical & Aerospace Engineering Dept., SJSU 20 ANSI Tables for Fits Clearance fits (Locational) – LC1 to LC11

ANSI Tables for Fits : 

Ken Youssefi Mechanical & Aerospace Engineering Dept., SJSU 21 ANSI Tables for Fits Interference fits (Force and Shrink fits) – FN1 to FN5 0.75 +.8 +0.0 +1.9 +1.4

Geometric Tolerancing : 

Ken Youssefi Mechanical & Aerospace Engineering Dept., SJSU 22 Geometric Tolerancing Geometric Dimensioning and Tolerancing (GDT) GDT defines the features of a part more efficiently than just the size. It also defines the standards for verifying the specified size and form. ANSI Y14.5-1994

Geometric Tolerancing : 

Ken Youssefi Mechanical & Aerospace Engineering Dept., SJSU 23 Geometric Tolerancing Geometric tolerancing is a system that specifies the form, profile, orientation, and location of part’s features using the ANSI standards.

Geometric Tolerancing - Examples : 

Ken Youssefi Mechanical & Aerospace Engineering Dept., SJSU 24 Geometric Tolerancing - Examples Form tolerancing Flatness

Geometric Tolerancing - Examples : 

Ken Youssefi Mechanical & Aerospace Engineering Dept., SJSU 25 Geometric Tolerancing - Examples Orientation tolerancing Perpendicularity

Geometric Tolerancing - Examples : 

Ken Youssefi Mechanical & Aerospace Engineering Dept., SJSU 26 Geometric Tolerancing - Examples Location tolerancing Concentricity

Slide 27: 

Ken Youssefi Mechanical & Aerospace Engineering Dept., SJSU 27 Exam 1 – Friday Oct. 6, 9-10 (E-341) Type of problems 3D views - given the three standard views, draw an oblique or isometric views. 2D views - given an isometric view of an object, draw the three standard views (front, top and right side). Missing line problems - given standard views of an object with some features missing, draw the missing features. All views are drawn freehand, no straight edge. Bring soft pencil and eraser, paper will be provided. Section views – definition and standards. Dimensioning standards and conventions. 3D visualization.