MAE 1351 EXAM 3

Total runout (runout tolerance)[two arrows]

3D control for rotating parts relative to a datum axis. (cylindrical surface = controls circularity, straightness, taper, concentricity, and surface profile; flat surface = controls wobble, perpendicularity, and flatness)

Basic dimensions (those with a box around them)...

are theoretically exact and locate the perfect position of features from clearly identified datums

The feature control frame

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

Free running fit

not for use where accuracy is essential, but are good for large temperature variations, high running speeds, and heavy journal pressures

A dimension is expressed to the same number of inches of decimal places as its ________. Zeros are added to the _____ of the decimal point where necessary

tolerance; right

ASME stands for

American Society of Mechanical Engineers

Most drawings conform to the ______ system or they conform to the ____ system

SI; U.S. Customary

Where the dimension is less than one millimeter...

a zero precedes the decimal point

Where the dimension is a whole millimeter...

neither the decimal point nor the zero is shown

Where the dimension exceeds a whole number by a decimal fraction of one millimeter...

the last digit to the right of the decimal point is not followed by a zero

T/F commas and spaces shall be used to separate digits into groups in specifying millimeter dimensions on drawings

false

T/F A zero is not used before the decimal point for values less than one inch

true

contour rule or contour dimensioning

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

T/F Dimensions should appear multiple times in different views on a drawing

false, they should only apper once

Dimensioning and tolerancing shall be complete so that...

there is full understanding of the characteristic of each feature

circles are typically dimensioned as

diameters

arcs are dimensioned as

radii

T/F you should give dimensions between holes vs dimensioning the holes from the end of the part

True

Baseline Dimensioning

all of the dimensions in a given direction originate from a base or datum (frequently used for CNC machines)

Chain Dimensioning

features are dimensioned relative to one another (used when a part function requires that features be related to one another)

T/F chain dimensioning is often preferred over baseline

False, Baseline dimensioning is prefrred

Chain dimensioning usually yields the _______ accumulation of tolerance between features,where the maximum distance between features is...

largest; equal to the sum of the intermediate distances

dimension only to _______ or _______ lines

visible; solid

Dimension lines also should be at least _____ ___ from any view, helping to avoid clutter.

10 mm

When dimensions are placed outside other dimensions, there should be at least ___ ___ between dimension lines

6 mm

When dimensioning a visible gap of at least ___ ___ should be between extension lines and object geometry

1 mm

when dimensioning, extension lines should extend ___-___ ___ past their corresponding dimension line

2-3 mm

Chamfersy are dimensioned by

giving a length from the end of the part and an angle or by specifying two distances

|___| represents what on a drawing?

counterbore

\/ represents what on a drawing?

countersink

a line with an arrow pointing down represents what on a drawing?

specifying depth

Unless otherwise specified, all geometric tolerances apply for...

full depth, length, and width of the feature

notes typically appear in the _____________________ corner of a drawing and apply to the whole drawing

lower right-hand corner

Wires, cables, sheets, rods, and other materials manufactured to gage or code numbers shall be specified by ________ ________ indicating the diameter or thickness

linear dimensions

a 90° angle applies where centerlines and lines depicting features are...

shown on a drawing at right angles by basic dimensioning and no angle is specified

Dimensions and tolerances apply only at the drawing level where...

they are specified

A dimension specified for a given feature on one level of drawing is

not mandatory for that feature at any other level

All dimensions and tolerances apply in a _____ _____ condition (this principle does not apply to non-rigid parts)

free state

In an engineering drawing, every dimension must have a tolerance. True?

yes, every single one

Best practice is to dimension hole features in the view where they show in the drawing as...

circles

Best practice is to dimension cylindrical (solid) features in the view where they show as...

rectangles

The nomenclature "TYP" or "TYPICAL OF" indicates...

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

dimensions in an engineering drawing are assumed to be at...

room temperature and pressure

In a unilateral tolerance, all of the deviation...

is in one direction from the basic size

T/F a unilateral tolerance is all above the basic size of the dimension

Flase, it is either above or below

T/F For metric dimensions, a single zero is shown without a plus or minus sign

True

T/F When a designer is dimensioning in inches, the tolerance value is expressed with the number of decimal places that the designer deems necessary

false, it is expressed with the same number of decimal places as the basic size with the appropriate plus or minus size

Bilateral tolerances are tolerances where the deviation..... and is equally or unequally distributed about the basic size.

is divided in some way above and below the basic size of the dimension

Limit dimensions are tolerances where the deviation...

is displayed with the high limit above the low limit

Baseline dimensioning can eliminate some of the accumulation of tolerances where the maximum variation between two features is the...

sum of the tolerances on the two dimensions from their origin to the two features

Direct dimensioning yeilds the ______ accumulation of tolerances. This method involves placing...

smallest; a single dimension between two key points to minimize the tolerance accumulation

Statistical tolerancing

a way to assign tolerances based on sound statistical practices rather than conventional tolerancing practices

state a problem with statistical tolerancing

it usually results in tolerance values being more restrictive than necessary

When manufacturing processes are monitored by statistical process controls, technicians and engineers are better informed about...

processes for which tolerance values can be increased to reduce manufacturing costs

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

Transition fits are typically associated with...

selective assembly

Selective Assembly:

involves measuring parts after they are machined and matching them up with appropriate mating parts

With transition fits, tolerances can be _________ so that manufacturing the individual parts is less expensive.

made larger

Allowance:

the difference between the maximum material limits of mating parts

Tolerance:

The total permissible variation in a size or location dimension.

basic size

the size from which the limit dimensions were derived

Hole basis or basic hole system

the basic size is applied to the lower limit of the hole and is frequently used

Shaft basis or basic shaft system

the basic size is applied to the upper limit of the shaft and is used when several parts are required to fit on a shaft

English fits include:

RC, LC, LT, LN, FN

Running or sliding clearance fit(RC)

these fits provide a similar running performance, with suitable lubrication allowance, throughout the range of sizes

Locational Clearance Fits(LC)

these fits are intended for parts that are normally stationary but can be freely assembled or disassembled

Locational transition fit(LT)

these fits are intended where accuracy of location is important but a small amount of clearance or interference is permissible

Locational interference fit(LN)

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

Force or shrink fit(FN)

these fits are usually characterized by maintenance of constant bore pressures throughout the range of sizes

Metric Fits include

Loose running fit, Free running fit, close running fit, sliding fit, locational clearance fit, locational transition fit, locational interference fit, medium drive fit, force fit

Loose running fit

these fits are used for wide commercial tolerances or allowances on external members

Close running fits

these fits are for running on accurate machines and ensuring accurate location at moderate speeds and journal pressures

sliding fit

these fits are not intended to run freely, but are intended to move and turn freely and locate accurately

Locational Clearance Fits

these fits provide a snug fit for locating stationary parts; they can be freely assembled and disassembled

locational transition fit

these fits provide for accurate location and a compromise between clearance and interference

locational interference fit

these fits are for parts requiring rigidity and alignment with prime accuracy of location but without special bore pressure requirements

medium drive fit

these fits are for ordinary steel parts or shrink fits on light sections—the tightest fit usable with cast iron

force fit

these fits are suitable for parts that can be highly stressed or for shrink fits where the heavy pressure forces required are impractical

Follow these guidelines to determine an English fit:

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 shaft

5) Remember that values on the English tables are in thousandths of an inch

Follow these guidelines to determine metric fits:

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 shaft

list some advantages of GD&T:

The system allows the designer to clearly specify design intent, communicate better, and leaves little room for misinterpretation

What two items are required for GD&T?

A datum reference frame, and specific form, orientation, and location tolerances that describe 2-D and 3-D tolerance zones

errors related to GD&T have something to do with...

how the datum reference frame was established

A cat's whisker measures:

.004 in

Human hair measures around 80 microns (high side). The closest inch equivalent is:

.001

The thickness of a "regular" sheet of paper is approximately:

about 3-4 thousandths

My machinist claims to be able to hold a particular dimension to 5 tenths. She means...

.0005

A supplier says they carry "3 mil" plastic sheet stock. This means:

It has a thickness of 3 millimeters

My drawing has a dimension that reads as follows: .075 ± .02. This means that...

the designer did not pay attention in class

I'm designing a part and need a running fit between a ½" shaft and a hole. I'll assign my tolerances based on this fit category:

RC

The primary datum plane is established by...

a minimum three-point contact with the back surface of the object.

The secondary datum plane is established by....

a two-point contact with the bottom surface, perpendicular to the primary datum surface

The tertiary datum plane is established by...

a one-point contact with the right-hand surface, perpendicular to the primary and secondary datum surfaces

Maximum Material Condition (MMC)

the condition in which a feature of size contains the maximum amount of material within the stated limits of size (counterpart is LMC)

Form tolerances

are for individual features and are not related to any datums (includes straightness, flatness, circularity [circle], and cylindricity [circle w/ line on either side]) and may be 2D or 3D

Profile of a line (profile tolerance) [open half circle]

specifies a 2D tolerance zone defined by two contours. When datums are specified, the tolerance controls the shape and size and/or location of the contour. When datum is not specified, it controls only the shape of the contour

Profile of a surface (profile tolerance) [closed half circle]

specifies a 3D tolerance zone defined by two contoured surfaces. When datums are not specified, the tolerance controls only the shape of the contour. When datums are specified, the tolerance controls the shape and size and/or location of the contour

Inspection of profile tolerances methods include:

Optical comparitors with overlay charts (thin parts) and mechanical gaging (master part guides dial indicator as it traces the surface of the part), datums