Engineering Design Module 4 (second set)

Flashcards about dimensioning

ANSI Y14.5

The accepted national standard in the USA for dimensioning. It outlines uniform practices for displaying and interpreting dimensions and related info on drawings and other forms of engineering documentation

Dimension

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

Arrowhead

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

Dimension Line

A thin, dark, solid line that terminates at each end with arrowheads. The value of a dimension typically is shown in the center of the dimension line. Together with its arrowheads, it shows the direction and extent of a dimension

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

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

Baseline Dimensioning

All of the dimensions in a given direction originate from a base of datum

Chain Dimensioning

Features are dimensioned relative to one another

Contour Dimensioning

Showing dimensions in the view where the contour or shape of the object shows up the best is a good global rule to follow

Chamfers

Are beveled or angled edges that typically appear on the ends of shafts or fasteners to aid in assembling parts or to smooth out rough edges. Dimensioned by giving a length from the end of the part and an angle or by specifying two distances.

General notes

Typically appear in the lower right-hand corner of a drawing and apply to the whole drawing and some maybe located in a title block

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

Statistical Tolerancing

A way to assign tolerances based on sound statistical practices rather than conventional tolerancing practices (can be applied only when appropriate statistical process control methods are used for manufacturing)

Clearance fit

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

Interference fit

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

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

Allowance

Allowance is the difference between the maximum material limits of mating parts. It is the minimum clearance or maximum interference between parts

Tolerance

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

Basic Size

The size from which the limit dimensions were derived

Clearance

Refers to a fit where there is space between the two mating parts.

Interference

A fit where the two mating parts have intersecting nominal volumes, requiring the deformation of the parts

Hole Basis or Basic Hole System

In this system, the basic size is applied to the lower limit of the hole

Shaft Basis or Basic Shaft System

In this system, the basic size is applied to the upper limit of the shaft

RC-Running or sliding clearance fit-

These fits provide a similar running performance, with suitable lubrication allowance, throughout the range of sizes. The clearances for the first two classes (RC1 and RC2), used chiefly as slide fits, increase more slowly with the diameter than the other two classes do; thus, accurate location is maintained even at the expense of free relative motion

LC- 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

LT- 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

LN- 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. Such fits are not intended for parts designed to transmit frictional loads from one part to another by virtue of the tightness of fit, as these conditions are covered by force fits

FN- 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

Geometric dimensioning and tolerancing (GD&T)

3-D mathematical system that allows a designer to describe the form, orientation, and location of features on a part within precise tolerance zones

Datum reference frame

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

Feature control frame

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

Maximum material condition (MMC)

Condition in which a feature of size contains the maximum amount of material within the stated limits of size

Least Material Condition (LMC)

Condition in which a feature of size contains the minimum amount of material within the stated limits of size

Flatness

Specifies a 3-D tolerance zone defined by two parallel planes (all points on specified surface must fall between the two imaginary planes)

Circularity (roundness)

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

Cylindricity

Controls a cylindrical surface so that all points are equidistant from a common axis

Profile of a line

Specifies a 2-D tolerance zone defined by two contours

Profile of a surface

Specifies a 3-D tolerance zone defined by two contoured surfaces

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 (when applied to a surface, the 3-D zone is defined by the area between two parallel planes; when applied to an axis, the 3-D zone is defined by the area within a cylinder)

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 (when applied to a surface, 3-D zone is defined by the area between two parallel planes; when applied to an axis, 3-D zone is defined by the area within a cylinder)

Circular runout

Two- D control similar to circularity or roundness (main difference is that circular runout controls a surface relative to a datum axis)

Shape

For single parts, it must conform to some semblance of size for compatibility to an environment or to fulfill its intended function

ASME and Y14.5

Technology developed to MIMINIZE AMBIGUITY in graphical engineering communication

True Design

Also means for precision; the less precise it needs to be to accomplish its objective the better

Dimension

Is the nominal number like 1 inch in the example