Tolerances

What is a tolerance?

A tolerance is an acceptable amount of dimensional variation that will still allow an object to function correctly.

What is the equation for allowance?

Allowance = MMC internal feature - MMC external feature

What is allowance?

Allowance is the minimum clearance or maximum interference between parts

Are datums required for location?

Always

Are datums required for orientation?

Always

Are datums required for runout?

Always

What is a tolerance chart called?

Standard Tolerance Chart

Who invented GD & T, what company was he from, and where was he from?

Stanley Parker, Royal Torpedo Factory, from Alexandria, Scottland

What is a transition fit?

Transition fit occurs when two mating parts can sometimes have a clearance fit and sometimes have an interference fit, like when you want a part to be held so securely, but not so secure as to prevent it from being disassembled ("Push Fit")

How many points of contacts are on a secondary datum?

Two

When are typical datum surfaces used?

Typical datum surfaces used when a part is going to be machined on a vertical mill

What are tolerances typically specified on?

Typically tolerances are specified based on the number of digits to the right of the decimal point in a dimension

What categories are under the orientation tool?

parallelism perpendicularity angularity

What categories are under the profile tool?

profile surface profile line

What do direct tolerances well and work against on?

size location

What categories are under the form tool?

straightness flatness circularity cylindricity

0.126 _____ limit 0.125 _____ limit

upper lower

What is the primary datum references on position tolerance callout represented by?

A B or C

Are datums required for profile?

Sometimes

How do you find the lower limit?

Specified Dimension + negative variance

How do you find the upper limit?

Specified Dimension + positive variance

What is a specified dimension?

Specified Dimension is the target dimension from which the limits are calculated

What are the fore major geometric characteristics?

location orientation size form

How far should you specify dimensions?

Specify dimensions only to the precision and tolerance necessary for the part to function properly

Would interchangeable parts be possible without tolerance?

No

Which one is the specified dimension? 1.50±.05

1.50

What tolerance is allowed in limit dimensions?

Any size between or equal to the upper limit and/or lower limit is allowed

What has no tolerance, why, and what are they indicated by?

Basic Dimensions have no tolerance. They are "exact" dimensions. They are signified by placing a box around them.

What is the geometric control symbol on position tolerance callout represented by?

Circle with two lines one vertical and the other horizontal

What does a clearance fit do?

Clearance Fit limits the size of mating parts so that a clearance always results when mating parts are assembled. This type of fit allows for sliding or motion between two mating parts.

What is the second step to using GD & T?

Control the Datum features as required - Datum features are features on the part, and like all other features, must be controlled.

What does GD & T use?

Cylindrical, rather than square tolerance zones for the positioning of circular features.

What can dimensions be?

Directly or indirectly toleranced

What do directly toleranced dimensions use?

Directly toleranced dimensions, use the tolerances called out in the drawing format, or have the tolerance included in the dimension.

How many points of contacts are on a primary tertiary?

One

Before interchangeable part, what was the only way to create precise assemblies?

Fitting

What does location always control?

Orientation

What does the allowance have to be for a clearance fit?

For a clearance fit, the allowance is the tightest possible fit, or smallest space, between mating parts.

What does size usually control?

Form

What are GD & T tools used for?

GD & T tools can be used to control several aspects of a feature.

What does GD & T stand for?

General Dimensions and Tolerances

What are general tolerances?

General tolerances are tolerances that are assumed if no specific tolerance is given for a dimension.

What do tolerances on specified drawings do?

Helps to define the manufacturing process and control the variation between copies of the same part

If a whole, what does 1.50 ± .05 mean?

Hole location can be .05 larger or smaller than 1.50

What does Parker's system do?

Parker's system saves usable parts that would not normally pass inspection and be consequently rejected.

What is the first step to using GD & T?

Identify Datum Features - establishes origins of measurement

What do overly precise dimensions and overly tight tolerances do?

Increase manufacturing costs

What do indirectly toleranced dimensions use?

Indirectly toleranced dimensions are BASIC dimensions. Appropriate tolerances are called out in a Feature Control Frame.

What is an interference fit?

Interference Fit limits the size of mating parts so that an interference always results when mating parts are assembled, like in a "press fit", where two pieces are assembled with the intention that they stay assembled.

What does LMC stand for?

Least material condition

What is LMC?

Least material condition (LMC) is the condition of a part when it contains the smallest amount of material.

What are the three basic tolerances?

Limit Dimensions Bilateral Tolerance Unilateral Tolerance

What are limits?

Limits are the maximum and minimum sizes shown by the toleranced dimension

What are the linear dimensions?

Linear Dimensions X.X = ± .1 X.XX = ± .03 X.XXX = ± .010 Angles = ± .5°

What is the third step to using GD & T?

Locate other features to the datum reference framework - once established, all other features on the part must be located relative to the datum features.

What is a lower limit?

Lower limit is the minimum allowable dimension

What is a machine's tolerance?

Machine's potential to cope with changes

What does MMC stand for?

Maximum material condition

What is the MMC?

Maximum material condition (MMC) is the condition of a part when it contains the largest amount of material.

Are datums required for form?

Never

Are any two parts identical?

No

Are datums required to control Form - flatness, straightness, circularity and cylindricity, datums are not required?

No

Is variation unavoidable?

No

What are the three datums?

Primary Secondary Tertiary

What does the proper application of GD & T ensure?

Proper application of GD&T will ensure that the allowable part and assembly geometry defined on the drawing leads to parts that have the desired form and fit and function as intended.

What do limit dimensions provide?

Provide an upper limit and lower limit for the dimension

What does a unilateral tolerance provide?

Provides an allowable variation in only one direction (either larger or smaller)

What do bilateral tolerances provide?

Provides an equal allowable variation, larger and smaller

Where a measurements made from?

Reference Plane

What is the lower limit of an internal feature?

The diameter of a hole

What is the upper limit of the diameter dimension?

The diameter of a hole

If a whole, what does this mean?: +.400 -.000

The hole diameter may vary .004 larger but may not be smaller than .500

What is the upper limit of an external feature?

The length of a plate

What must be specified on a technical drawing?

The limits of allowable variation

What is the lower limit of an external feature?

The lower limit of the dimension

What do tolerancing standards describe?

Tolerancing standards describe how to inspect parts for quality, and reliability.

What is the purpose of GD & T?

The purpose of GD&T is more accurately defined as describing the geometric requirements for part and assembly geometry.

What is the task of fitting?

The task of fitting is making skilled cuts to parts, on a cut-and-try basis (cut, try; cut more, try again), so that they will fit together with the desired degree of fit.

What is the tolerance in terms of total variance?

The tolerance is the total variance in a dimension and is equal to the difference between the upper and lower limits.

How many datums are usually on a part?

Three

How many points of contacts are on a primary datum?

Three

What is required to control the profile of a line?

To control the profile of a line or of a surface, you may or may not require a datum surface.

What is the equation for tolerance?

Tolerance = Upper Limit + Lower Limit

Why do we need tolerances?

Tolerances assures parts interchangeability Tolerancing simplifies parts inspection

What are applied to mating parts in an assembly?

Tolerances?

What is an upper limit?

Upper limit is the maximum allowable dimension

What specifies the allowable variation in bilateral tolerances?

Uses a plus/minus (±) symbol to specify the allowable variation

What signs does unilateral tolerance use?

Uses separate plus (+) and minus (-) signs

What does using tolerances mean?

Using tolerances means that we get the same part every time, regardless of where it is made

What is every feature on every manufactured part is subject to?

Variation

What is the AMSE Standard?

Y14.5 - 2009

Do ALL dimensions need a tolerance?

Yes

What must you use to control Location - position, concentricity, and symmetry; Orientation - parallelism, perpendicularity and angularity; Runout - circular or total runout?

You must use datum surfaces as references.

What categories are under the runout tool?

circular runout total runout

What categories are under the location tool?

concentricity position symmetry

What is the tolerance on position tolerance callout represented by?

diameter symbol and number

What is the machine's potential to cope with changes?

dimensional environmental physical property of material

What is the tolerance modifier on position tolerance callout represented by?

either m or l in a circle

What are the 5 types of tools?

form profile orientation location runout

What is indicated on a positional tolerance callout?

geometric control symbol tolerance tolerance modifier primary datum reference secondary datum reference tertiary datum refernce