1. Tolerancing Engr 135

2. Tolerance Theory
Tolerances are used to control the variation that exists on all manufactured parts.
The amount that each part is allowed to vary in size and shape depends on the end use of the part.
How would the tolerances of parts for a children’s bicycle compare to the tolerances of parts for a supersonic jet aircraft?

3. Tolerance Values 4.252 4.248 The dimension for a part is given as:
4.250 ±0.002
What is the upper limit (largest value) allowable for the part?
What is the lower limit (smallest value) allowable for the part?
The upper and lower allowable sizes are called limit dimensions.
4.252
4.248

4. Tolerancing and Design
Tolerancing enables an engineer to design parts that are interchangeable, or parts that may be replaced.
For example, you expect to be able to purchase new brushed aluminum wheels for your car and have them be an identical replacement of your factory rims.

5. Interchangeability
Tolerances are assigned to the dimensions of parts that are mated together. This allows for the interchangeability of parts with like parts.
We are not only concerned with the size of a part but also the variation in the size of a part.

6. Manufacturing Parts
Tolerances are necessary because it is impossible to manufacture parts without some degree of variation.
We want to be able to manufacture parts in different locations and different time and still be able to put them together in a functional assembly. (For example, Boeing 787)

7. Tolerancing Standards
ANSI/AMSE
American National Standards Institute
American Society of Mechanical Engineers
ISO
International Standards Organization

8. Manufacturing Tolerances
Why are manufacturing tolerances important for LEGOs?
LEGO reports their tolerance in some cases to be mm

9. Wikipedia on LEGOs
Bricks, beams, axles, mini figures, and all other elements in the Lego system are manufactured to an exacting degree of tolerance. When snapped together, pieces must have just the right amount of "clutch power"; they must stay together until pulled apart. They cannot be too easy to pull apart, or the resulting constructions would be unstable; they also cannot be too difficult to pull apart, since the disassembly of one creation in order to build another is part of the Lego appeal. In order for pieces to have just the right "clutch power", Lego elements are manufactured within a tolerance…

10. Tolerance Types Limit Dimensions Plus-Minus Dimensions
Page or Block Tolerances

11. Limit Dimensions
Limit Dimensions are the maximum and minimum size a part can be and still be a functional part.
The largest number is always place first or on top.

12. Plus or Minus Dimensions
Plus or minus dimensions give a basic size and the variation that can occur around that basic size.

13. Page or Block Dimensions
A page tolerance is actually a general note that applies to all dimensions not covered by some other tolerancing type.
These are usually found in the general notes or in the title block of a drawing.