Engineering Dimensioning and Tolerancing Flashcards

A comprehensive set of flashcards covering key concepts and rules related to engineering dimensioning, tolerancing, and geometric dimensioning and tolerancing (GD&T) as per ASME Y14.5 and other relevant standards.

What is the accepted national standard in the USA for dimensioning?

ANSI Y14.5, published by the American Society of Mechanical Engineers (ASME)

What are the standard units for engineering drawings according to the international system of units (SI)?

Millimeters

What are the four rules for metric drawings (millimeters) standard unit?

1. Use a zero before the decimal point for values less than one millimeter. 2. Do not show the decimal point or zero for whole numbers. 3. Do not follow the last digit to the right of the decimal point with a zero. 4. Do not use commas or spaces to separate digits into groups.

What are the two rules established for decimal inches?

1. Do not use a zero before the decimal point for values less than one inch. 2. Express a dimension to the same number of decimal places as its tolerance, adding zeros to the right of the decimal point where necessary.

According to ASME Y14.5, what are the fundamental rules for dimensioning?

1. Each dimension must have a tolerance. 2. Dimensioning and tolerancing must be complete for full understanding. 3. Each necessary dimension of an end product must be shown; no more dimensions than necessary. 4. The drawing should define a part without specifying manufacturing methods.

Define 'dimension' according to ASME Y14.5.

A numerical value expressed in appropriate units of measure to define the size, location, geometric characteristic, or surface texture of a part or part feature.

Define 'arrowhead'.

A small triangle at the end of dimension lines and leaders to indicate the direction and extent of a dimension.

Define 'dimension line'.

A thin, dark, solid line that terminates at each end with arrowheads; shows the direction and extent of a dimension.

Define 'extension line'.

A thin, dark, solid line extending from a point on an object, perpendicular to a dimension line, used to indicate the extension of a surface or point to a location preferably outside the part outline.

Define 'leader'.

A thin, dark, solid line terminating with an arrowhead at one end and a dimension, note, or symbol at the other end; used to direct a dimension, note, or symbol to the intended place on a drawing.

What is the rule regarding the inclusion of dimensions on a drawing?

Only include the dimensions that are necessary to manufacture the part, and each dimension should appear only once.

What is the 'Contour Rule'?

Each dimension should be placed in the view where the contour shape is best shown.

What should happen to the overall dimension if 'inside' dimensions are more important or critical?

The overall dimension should be identified as a reference dimension, and reference dimensions are put into parenthesis.

Why is it important which dimensions are given even if all the geometry is defined?

Because when drawings are used to document parts for manufacturing, accepted rules and practices must be followed for proper results.

How are circles and arcs dimensioned?

Circles are dimensioned as diameters, and arcs are dimensioned as radii.

Why are circles dimensioned with diameters?

Because they typically represent machined holes, and machined holes are produced with standard tools defined by diameter dimensions.

What is the best way to begin determining which dimensions are most important?

Starting with an examination of how the part will function within the assembly.

Explain 'baseline dimensioning'.

A dimensioning method where all dimensions in a given direction originate from a base or datum, frequently used for CNC machines.

Explain 'chain dimensioning'.

A dimensioning method where features are dimensioned relative to one another, appropriate when part function requires features to be related.

When dimensioning parts, what kind of dimensions should you select?

You should select dimensions that can be measured.

What is the 'global rule' to follow when showing dimensions?

Showing dimensions in the view where the contour or shape of the object shows up the best.

What is the rule regarding dimensioning to visible or solid lines?

Dimension only to visible or solid lines.

What is the recommended minimum distance that dimension lines should be located from views?

At least 10mm (.375 inches) to avoid clutter.

What is the recommended visible gap between extension lines and object geometry?

1mm (.0625 inches) is a good rule of thumb.

What font is required for engineering drawings?

Single-stroke gothic lettering, with uppercase letters.

What is the shift in engineering drawings regarding notes and symbols?

Shift toward the use of symbols to define features on drawings rather than notes written in English.

How are circles and arcs dimensioned using symbols?

Circles are dimensioned with Ø, and arcs are dimensioned with R.

What is the function and dimensioning of 'chamfers'?

Chamfers are beveled or angled edges dimensioned by giving a length from the end of the part and an angle, or by specifying two distances.

Describe how to read the following symbols: |_|, \/, ↓.

|_| represents a counterbore, \/ represents a countersink, ↓ used for specifying depth.

Where do general notes typically appear on a drawing?

General notes typically appear in the lower right-hand corner of a drawing and apply to the whole drawing; some may be located in a title block.

What are local notes?

Local notes appear on the drawing views and are usually specified with a leader line, used to specify info that cannot be shown with regular dimensions.

What is the benefit of constraint-based modelers regarding dimensioning?

The ability of the software to let you know when geometry has been under dimensioned or over dimensioned.

What is the accepted standard for dimensioning practice?

ASME Y14.5M-1994

What is the rule regarding dimensions identified as reference, maximum, minimum, or stock?

Each dimension shall have a tolerance, except for those dimensions specifically identified as reference, maximum, minimum, or stock (commercial stock size).

What angles apply where center lines and lines depicting features are shown on a drawing at right angles and no angle is specified?

A 90° angle applies.

Unless otherwise specified, to what temperature do all dimensions apply?

20°C (68°F)

In what condition do all dimensions and tolerances apply to?

All dimensions and tolerances apply in a free state condition.

Where do dimensions and tolerances apply?

Dimensions and tolerances apply only at the drawing level where they are specified.

What are the common formats for tolerance dimensions?

Unilateral, bilateral, and limit dimensions.

What is a unilateral tolerance?

A tolerance where all of the deviation is in one direction from the basic size, either all above or all below.

What is a bilateral tolerance?

A tolerance where the deviation is divided in some way above and below the basic size of the dimension, equally or unequally distributed.

How are limit dimensions displayed?

With the high limit above the low limit, or if on a single line, the low limit appears before the high limit.

What is tolerance buildup?

The accumulation of tolerances which can occur in several ways when using tolerance dimensions.

Which dimensioning method usually yields the largest accumulation of tolerance between features?

Chain dimensioning

How can baseline dimensioning eliminate some of the accumulation of tolerances?

The maximum variation between two features is the sum of the tolerances on the two dimensions from their origin to the two features.

What is the best way to eliminate tolerance accumulation?

Direct dimensioning, which involves placing a single dimension between two key points to minimize tolerance accumulation.

What is statistical tolerancing?

A way to assign tolerances based on sound statistical practices rather than conventional tolerancing practices, applicable only when appropriate statistical process control methods are used for manufacturing.

What is the key focus relating to 'fits' in design?

The intent of a design requires that you accurately specify fits between mating parts.

What are the three primary classifications of fits?

Clearance fit, interference fit, and transition fit.

What is a clearance fit?

Specifying the limits of size in such a way that a clearance or space always exists between mating parts.

What is an interference fit?

Specifying the limits of size in such a way that an interference of material always exists between mating parts.

What is a transition fit?

Specifying the limits of size in such a way that either a clearance or interference fit will exist when mating parts are assembled.

What shop process is typically associated with transition fits?

Selective assembly

Define 'allowance' in the context of fits.

The difference between the maximum material limits of mating parts; the minimum clearance or maximum interference between parts.

Define 'tolerance' in the context of fits.

The total permissible variation of a size; the difference between the upper limit and the lower limit.

Define 'basic size' in the context of fits.

The size from which the limit dimensions were derived.

Define 'clearance' in the context of fits.

A fit where there is space between the two mating parts; the intent is that when assembled, the shaft will spin within the hole.

Define 'interference' in the context of fits.

A fit where the two mating parts have intersecting nominal volumes, requiring the deformation of the parts; the intent is that when assembled, the shaft will not spin in the hole.

What is the hole basis or basic hole system?

In this system, the basic size is applied to the lower limit of the hole. Used quite often since standard tools are designed to machine holes no less than a particular size.

What is the shaft basis or basic shaft system?

In this system, the basic size is applied to the upper limit of the shaft. The hole is then machined to create the desired type of fit. Used when several parts with different fits are required to fit on a particular shaft.

Name the five types of fits within the English, or inch, system?

RC-Running or sliding clearance fit, LC- Locational clearance fit, LT- Location transition fit, LN- Locational interference fit, FN- Force or shrink fit

What occurs during running or sliding clearance fit?

These fits provide a similar running performance, with suitable lubrication allowance, throughout the range of sizes. Accurate location is maintained even at the expense of free relative motion

What occurs during locational clearance fit?

These fits are intended for parts that are normally stationary but can be freely assembled or disassembled. They range from snug fits for parts requiring accuracy of location to medium clearance fits for parts such as spigots to looser fastener fits where freedom of assembly is of prime importance

What occurs during location transition fit?

These fits are intended where accuracy of location is important but a small amount of clearance or interference is permissible. They are a compromise between clearance and interference fits.

What occurs during locational interference fit?

These fits are intended where accuracy of location is of prime importance and where parts require rigidity and alignment with no special requirement for bore pressure.

What occurs during force or shrink fit?

These types of interference fits are usually characterized by maintenance of constant bore pressures throughout the range of sizes. Therefore, the interference varies almost directly with diameter, and the difference between its minimum and maximum value is small to maintain the resulting pressures within reasonable limits

How would you specify an inch, or English, fit between a hole and a shaft form a standard table?

1. Determine the type of fit appropriate for the design and locate the corresponding table. 2. Determine the basic size of the parts. 3. Find the size range on the table. 4. Determine the tolerances for the hole and the shaft.

What is GD&T?

Geometric dimensioning and tolerancing (GD&T) is a 3-D mathematical system that allows a designer to describe the form, orientation, and location of features on a part within precise tolerance zones. It is an international language.

What are some advantages of using GD&T?

The system allows the designer to clearly specify design intent, there is better communication throughout the design process, and the system is set up so that almost nothing can be interpreted in more than one way.

What are the two elements required in a GD&T system?

1. A datum reference frame to immobilize and orient the part. 2. Specific form, orientation, and location tolerances that describe 2-D and 3-D tolerance zones within which all part geometry must fall.

What is a datum reference frame when working with GD&T?

A theoretical system made up of there mutually perpendicular planes, or datums, established by real features on the object.

What is the goal for adding datums to immobilize the part?

To eliminate all degree-of-freedom (translational and rotational)

What are datum simulators?

To establish theoretical datums, datum simulators must be used. Datum simulators can be a number of things such as machine beds, lathe chucks or collets, gage pins, and vises used to establish datums or granite tabletops, surface plates, and angle plates. These must be at least tens times better in quality than the tolerances specified on the drawings to be considered datum simulators

What are form tolerances?

Form tolerances are for individual features (not related to datums); profile tolerances may or may not be related to datums; orientation, location, and runout tolerances must be related to datums

What is a feature control frame?

Contains the geometric characteristic symbol, the geometric tolerance, and the relative datums.

What does the acronym MMC stand for?

Maximum material condition (MMC). Allows the size of the zone to change if the size of the hole changes, Condition in which a feature of size contains the maximum amount of material within the stated limits of size

What is the difference between Conventional Tolerancing and Basic Dimensions?

Main difference is that the locations of the holes are not dimensioned with limit dimensions, but with basic dimensions. Are theoretically exact. Locate the perfect position of features from clearly identified datums

Name the Form Tolerances

Includes straightness, flatness, circularity (roundness), and cylindricity

What surface must all points on specified by the flatness tolerance must fall?

Points must fall between two imaginary planes.

What is a Functional Guage?

if you are inspecting the straightness of an axis for a shaft used that if the shaft can pass through the hole, the part is acceptable

Describe circularity (roundness)

For shafts, all points within any plane perpendicular to the axis of the shaft must be equidistant from that axis.

Define 'cylindricity'.

The cylindricity tolerance controls a cylindrical surface so that all points are equidistant from a common axis. Is defined by two concentric cylinders

What is Profile of a line?

Specifies a 2-D tolerance zone defined by two contours that may or may not specify a datum reference but controls the shape of the contour when no datums are specified

What is Profile of a Surface?

Specifies a 3-D tolerance zone defined by two contoured surfaces (like profile of a line, tolerance may specify a datum reference) When a datum reference is not specified, the tolerance controls only the shape of the contour

What is Parallelism?

Specifies 3-D tolerance zone that can control the orientation of a surface or axis of a hole or cylinder relative to a datum

What is Perpendicularity?

Specifies 3-D tolerance zone that can control the orientation of a surface or axis of a hole or cylinder relative to a datum

What is Angularity?

3-D tolerance zone that can control the orientation of a surface or axis of a hole or cylinder relative to a datum and can include a basic dimension specifying the angle from one or more datums.

What is Position Tolerance?

When the location of a hole or cylindrical feature of size needs to be controlled, position establishes a 3-D cylindrical tolerance zone within which the axis of the feature must fall.

What if Concentricity?

Geometric tolerance used to control the axis to axis relationship between two features

What is Symmetry?

Concerned with the position of the center plane relative to an axis or a center plane of a datum feature

What is runout tolerances?

Controls a surface relative to a Circular runout and Total runout which is 3-D control for rotating parts relative to a datum axis

While using SolidWorks when adding dimension text what can it add to the object?

Add “4X or GOES THRU ALL” by clicking on the dimension and opening the menu and finding “dimension text” and adding what you want.

What is a Dimension?

Dimension is the nominal number like 1 inch in the example

What is a Tolerance?

Tolerance is the acceptable range of variability that will still guarantee that our design will perform as intended

What does specify dimensions that can be easily set up for manufacturing, and can be easily measured for inspection mean?

Dimensions which are dealing with design intent are the most difficult. Challenge yourself: does my choice of dimension reflect how I intend for parts to be made and assembled, so that the device works?

When it comes to ASME Y14.5 Dimensioning Rules what are the rules?

Every feature shall be explicitly and fully dimensioned leaving nothing to assumption. Each necessary dimension shall be shown; no redundant dimensions allowed (Exceptions: some reference dimensions allowed (as few as possible)). Each dimension shall have a tolerance (Exceptions: stock, ref. Tolerance can be specified locally or globally

What is Baseline dimensioning?

Establishing the top and right edge of the part All the vertical dimensions are done to the vertical edge and all the horizontal dimensions are done to the horizontal edge. Right and top edges are datums

What is Chain dimensioning?

Building the dimensions off of one another instead of a common datum causes tolerances to accumulate since the first dimension has a tolerance and when you build off that dimension it accumulates that tolerances and adds it to its own

What is a filleted dimensioned as?

Radius

What is “TYP” or “TYPICAL OF”?

That a feature is repeated exactly in the drawing a certain number of times