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General Tolerance and Hole Fit

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Presentation on theme: "General Tolerance and Hole Fit"— Presentation transcript:

1 General Tolerance and Hole Fit
Instructors Name Course Number Copyright - Planchard 2012

2 Tolerance Standards The two most common Tolerance Standard agencies are: American National Standards Institute (ANSI) / (ASME) International Standards Organization (ISO) Copyright - Planchard 2012

3 Tolerance - General Precision is the degree of accuracy required during manufacturing. It is unfeasible to produce any dimension to an absolute measurement. Discrepancy must be allowed or provided in the manufacturing process. Copyright - Planchard 2012

4 Tolerance – General (Cont:)
Higher Precision: On a drawing may ensure better quality of a product, but by doing so can and likely will increase the cost of the part. Could make it cost prohibited in being competitive with similar products. Copyright - Planchard 2012

5 Tolerance - General (Cont:)
Example: Consider a design that contains cast components. A cast part usually has two types of surfaces: 1.) Mating surfaces 2.) Non-mating surfaces Copyright - Planchard 2012

6 Tolerance - General (Cont:)
Mating surfaces act together with other surfaces, typically machined to a specified finish. Mating surfaces typical require higher precision on all corresponding dimensions. Copyright - Planchard 2012

7 Tolerance - General (Cont:)
Non-mating surfaces are usually left in the original rough-cast form. No significant connection with other surfaces. Copyright - Planchard 2012

8 Tolerance - General (Cont:)
Tolerance - Method of specifying the degree of precision. Tolerance in simple terms is the amount of size variation permitted and provides a useful means to achieve the precision necessary in a design. Copyright - Planchard 2012

9 Tolerance - General (Cont:)
Tolerancing ensure interchangeability in manufacturing. Companies can manufacture parts in various locations while maintaining the proper functionality and design intent. Copyright - Planchard 2012

10 Tolerance - General (Cont:)
Each dimension is allowed to vary within a specified amount. In assigning as large a tolerance as possible, without interfering with the functionality or design intent of a part, the production costs can be reduced; product can be competitive in the real world. Copyright - Planchard 2012

11 Tolerance - General (Cont:)
The smaller the tolerance range specified, the more expensive it is to manufacture. There is always a trade off in design. Can you name a few? Copyright - Planchard 2012

12 Tolerance - Drawings Drawings
The dimensions given on a drawing indicate the accuracy limits to manufacture the part. These limits are called tolerances and are given in decimal notation. Copyright - Planchard 2012

13 Tolerance - Drawings (Cont:)
Tolerances can be specified in various unit systems, but for ANSI, specifications are in English (IPS) and Metric (MMGS). Copyright - Planchard 2012

14 Tolerance - Drawings (Cont:)
Tolerances on decimal dimensions, are normally expressed in terms of one, two, three, or more decimal places. Can be provided on a drawing in several ways. One of the common methods of specifying a tolerance that applies on all dimensions is to use a note in the Title block. Copyright - Planchard 2012

15 Tolerance - Drawings (Cont:)
Title Block General tolerances are typically provided in the Title Block. The general tolerances are applied to the dimensions in which tolerances are not given in the drawing view. Copyright - Planchard 2012

16 Tolerance - Drawings (Cont:)
Local Tolerance vs. General Tolerance “Title block” A Local Tolerance note indicates a special situation which is not covered by the General Title box. A Local Tolerance is located in the drawing view (with the dimension) or out side the Title box. Copyright - Planchard 2012

17 Tolerance - Drawings (Cont:)
The three most common Local Tolerance types are: Limit Bilateral Unilateral Copyright - Planchard 2012

18 Tolerance - Drawings (Cont:)
Limit - When a dimension has its high (upper) and low (Lower) limits stated. In a limit tolerance, the high value is placed on top, and the low value is placed on the bottom as illustrated. Nominal Size When both limits are placed on one line, the low limit precedes the high limit. The tolerance for the dimension illustrated above is the total amount of variation permitted or .002in Copyright - Planchard 2012

19 Tolerance - Drawings (Cont:)
Limit - In the angle example - the dimension may vary between 60 ºand 59º45'. Note: Each degree is one three hundred and sixtieth of a circle (1/360). The degree (º) may be divided into smaller units called minutes ('). There are 60 minutes in each degree. Each minute may be divided into smaller units called seconds ("). There are 60 seconds in each minute. To simplify the dimensioning of angles, symbols are used to indicate degrees, minutes and second. Copyright - Planchard 2012

20 Tolerance - Drawings (Cont:)
Bilateral - Variation of size is in both directions. The dimensions may vary from a larger size (+) to a smaller size (-) than the basic dimension (nominal size). The basic 2.44" dimension as illustrated with a bilateral tolerance of +-.01" is acceptable within a range of 2.45" and 2.43". Nominal Size Copyright - Planchard 2012

21 Tolerance - Drawings (Cont:)
Unilateral - Variation of size in a single direction - either (+) or (-). The examples of Unilateral tolerances shown below indicate that the first part meets standards of accuracy when the nominal or target dimension varies in one direction only and is between 3.000" and 3.025". Nominal Size Copyright - Planchard 2012

22 Tolerance Nomenclature
Nominal Size: is the size used for general identification – not exact size. Actual Size: is the measured dimension. A shaft of nominal diameter 10 mm may be measured to be an actual size of mm. Copyright - Planchard 2012

23 Tolerance Nomenclature (Cont:)
Allowance - The minimum clearance space or maximum interference intended between two mating parts under the Maximum Material Condition (MMC). Basic dimension / Basic size - The theoretical size from which limits of size are derived. It is the size from which limits are determined for the size or location of a feature in a design. Copyright - Planchard 2012

24 Tolerance Nomenclature (Cont:)
Fit - The general term used to defined the tightness or looseness between two components. Least Material Condition (LMC) - The size of the part when it consists of the least material. Maximum Material Condition (MMC) - The size of the part when it consists of the most material. Copyright - Planchard 2012

25 Tolerance Nomenclature (Cont:)
Tolerance - The total permissible variation of a size. The tolerance is the difference between the limits Copyright - Planchard 2012

26 Other Tolerance Types in SolidWorks
To indicate min or max dimensions desired where other elements of design determine the other unspecified limit. Copyright - Planchard 2012

27 Tolerance Accumulation
The tolerance between two features of a part depends on the number of controlling dimensions and the dimensioning method. Copyright - Planchard 2012

28 Tolerance - Accumulation (Cont:)
The distance can be controlled by a single dimension or multiple dimensions. Copyright - Planchard 2012

29 Tolerance - Accumulation - Chain Dimensioning method
The maximum variation between two features is equal to the sum of the tolerances placed on the controlling dimensions. In this case (Chain Dimensioning method). Copyright - Planchard 2012

30 Tolerance - Accumulation - Chain Dimensioning method
What is the tolerance accumulation of this object between the two illustrated surfaces (A & B) using the Chain Dimensioning method? Copyright - Planchard 2012

31 Tolerance - Accumulation - Baseline Dimensioning method
What is the tolerance accumulation of this object between the two illustrated surfaces (A & B) using the Baseline Dimensioning method? Copyright - Planchard 2012

32 Tolerance - Accumulation (Cont:)
If the accuracy of the distance between surface A and B is important, which dimensioning method should we apply? WHY? Copyright - Planchard 2012

33 Fit - Hole Tolerance In the figure below, the tightest fit between the two parts will be when the largest shaft is fit inside the smallest hole. The Interference (Press) Fit between the two parts can be calculated as: Minimum Clearance (Allowance) = (MMC Hole) (MMC Shaft) = = -0.02in Maximum Material Condition (MMC) Copyright - Planchard 2012

34 Fit - Hole Tolerance (Cont:)
The loosest fit between the two parts will be when the smallest shaft dimension is fit inside the largest hole dimension. The maximum clearance between the two parts can be calculated as: Maximum Clearance (Allowance) = (0.50hole) - (0.47shaft) = 0.03in Maximum Material Condition (MMC) Copyright - Planchard 2012

35 Shaft - Hole Tolerance View the table below.
Nominal/Basic Size: is the size used for general identification – not exact size. Copyright - Planchard 2012

36 Tolerance - Definition
Maximum Material Condition (MMC): The MMC is the size of the part when it consists of the most material. Least Material Condition (LMC): The LMC is the size of the part when it consists of the least material. To fill in the below table. Note for the hole it is the lower number! Copyright - Planchard 2012

37 Fits Between Mating Parts
Fit is the general term used to signify the range of tightness in the design of mating parts. In ANSI/ASME Y 14.5M, four general types of fits are designated for mating parts: Clearance Fit Interference Fit Transition Fit Line Fit Copyright - Planchard 2012

38 Types of Fits Clearance Fit Interference (Press) Fit
Always a space for the fit. Min. Clearance > 0 Interference (Press) Fit Never a space. Max. Clearance  0 Lock and Key Door and Door frame Hinge pin Pin in a bicycle chain Copyright - Planchard 2012

39 Types of Fits (Cont:) Transition Fit Line Fit
Depending on the sizes (shaft and hole) there may be a space or not. Max. Clearance > 0 Min. Clearance < 0 Line Fit A space or a contact (hole diameter = shaft diameter) Min. Clearance = 0 Copyright - Planchard 2012

40 Geometric Dimensioning and Tolerancing
Geometric Dimensioning and Tolerancing is used to specify the shape of features. Things like: Straightness Flatness Circularity Cylindricity Angularity Profiles Perpendicularity Parallelism Concentricity And More... Geometric Tolerances are shown on a drawing with a feature control frame. Copyright - Planchard 2012

41 General Dimensional Tolerance
Think of Tolerance as defining a perfect form envelope that the real produced part must fit inside in order to be acceptable. This is why we need GD&T to address feature issues. Dimension tolerance does not say anything about the shape of the part! GDT controls the shape and the initial design intent. Variation of the feature Copyright - Planchard 2012

42 Hole Types, Symbols and Datums
Three perpendicular planes! Note: Datum A, B, & C. Copyright - Planchard 2012

43 Metric Drawing with GD&T
Datum Symbol Note: The Surface symbol and the datum Symbol! Copyright - Planchard 2012

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