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

Copyright - Planchard 2012

General Tolerance and Hole Fit

Instructors Name

Course Number


Tolerance Standards

• The two most common Tolerance Standard agencies are: – American National Standards Institute

(ANSI) / (ASME) – International Standards Organization (ISO)


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.


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.


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



• Mating surfaces act together with other surfaces, typically machined to a specified finish.

• Mating surfaces typical require higher precision on all corresponding dimensions.



• Non-mating surfaces are usually left in the original rough-cast form.

• No significant connection with other surfaces.



• 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.



• Tolerancing ensure interchangeability in manufacturing.

• Companies can manufacture parts in various locations while maintaining the proper functionality and design intent.



• 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.



• 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?


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.


Tolerance - Drawings (Cont:)

• Tolerances can be specified in various unit systems, but for ANSI, specifications are in English (IPS) and Metric (MMGS).



• 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.



• 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.



• 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.



• The three most common Local Tolerance types are: – Limit– Bilateral– Unilateral



• 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.

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

Nominal Size



• 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 smallerunits called minutes ('). There are 60 minutes in eachdegree. Each minute may be divided into smaller unitscalled seconds ("). There are 60 seconds in eachminute. To simplify the dimensioning of angles, symbolsare used to indicate degrees, minutes and second.



• 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



• 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


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 9.975 mm.


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.



• 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.



• Tolerance - The total permissible variation of a size. The tolerance is the difference between the limits


Other Tolerance Types in SolidWorks

To indicate min or max dimensionsdesired where other elements of design determine the other unspecified limit.


Tolerance Accumulation

• The tolerance between two features of a part depends on the number of controlling dimensions and the dimensioning method.


Tolerance - Accumulation (Cont:)

• The distance can be controlled by a single dimension or multiple dimensions.


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).


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?


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?


Tolerance - Accumulation (Cont:)

• If the accuracy of the distance between surface A and B is important, which dimensioning method should we apply? WHY?


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) = 0.49 - 0.51 = -0.02in

Maximum Material Condition (MMC)


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)


Shaft - Hole Tolerance

• View the table below.

Nominal/Basic Size: is the size used for general identification – not exact size.


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 itis the lower number!


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


Types of Fits

• Clearance 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


Types of Fits (Cont:)

• Transition 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)– Max. Clearance > 0– Min. Clearance = 0


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.


General Dimensional Tolerance

Think of Tolerance as defining a perfect form envelopethat the real produced part must fit inside in order to beacceptable. This is why we need GD&T to address featureissues. 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


Hole Types, Symbols and Datums

Three perpendicular planes! Note: Datum A, B, & C.


Metric Drawing with GD&T

Note: The Surface symbol and the datum Symbol!

Datum Symbol

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

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