4 dimension application and limits of size. gd&t: application and interpretation©...

4Dimension Application

and Limits of Size

GD&T: Application and Interpretation © Goodheart-Willcox Co., Inc.

• Clearly apply dimensions by complying with the stated general dimensioning guidelines.

• Apply dimensions to any of the geometric shapes commonly found on mechanical parts.

• Cite the categories for limits of fit and describe the general condition created by each category.

• Calculate and apply limits of size for mating features.

• Cite the two rules contained within ASME Y14.5.


• Provide examples of the effects that dimensions and tolerances have on manufacturing.

• Complete a surface condition specification when provided the allowable variations.


Cylinders

• Diameter and length required• Prefer dimensions on noncircular view• Diameter dimension usually between the views• Only one view may be necessary• Diameter symbol required for circular dimension


Cones

• Right circular cone– Base diameter and cone height– Base diameter and cone angle

• Oblique circular cone– Base diameter, cone height, apex offset


Holes—Specifying Diameter


Holes—Specifying Location

• Hole center• Centerlines and extension lines used

– Centerlines between holes– Extension lines beyond holes

• Dimensions on one side of view


Holes—Specifying Depth

• Assumed to go through part, unless depth is specified

• When not clear, use THRU• Use depth symbol for blind holes• Depth specified after the diameter


Holes for Machine Screws—Counterbore


Holes for Machine Screws—Countersink


Angles

• Angle specification notation– Degrees—30– Minutes—3015– Seconds—301528– Decimal—30.25

• Center of dimension line arc at vertex of angle• Extension lines, if extended, intersect at vertex

of angle


Chamfers

• Eliminates sharp edge• Facilitates assembly• 45° chamfers may be dimensioned by a note• Dimensioning chamfers other than 45°

– Dimension angle and length of one side– Dimension lengths of both sides of chamfer


Taper—Standard Specified


Taper—Taper per Inch Specified


Taper—Included Angle Specified


Features on Curved Surfaces

• Location– Angle– Chord– Arc length


Spherical Radii

• SR in front of dimension• Dimension to outside surface

– Easier to produce– Easier to verify


Irregular Curves


Symmetrical Features

• Only one side of symmetry line requires dimensions

• Two short lines across each end of center line indicates line of symmetry

• Partial or half views allowed


Machining Reliefs


Threads

• Minimum information– Nominal size– Threads per inch– Thread form– Thread class

• Example• .750-10UNC-2A


Knurls

• Machined on cylindrical shapes– Increase friction between parts– Improve grip and appearance

• Diametral pitch and shape required• Diameter before knurl required


Sheet Metal Bends

• Locate surface intersections or intersecting faces

• Specify inside or outside bend radius, but not both

• Material type and thickness dictates undimensioned bend radius


Sheet Metal Joggles

• Information needed– Location– Height– Length– Bend radius


Standard Sizes and Shapes

• Reduces production costs• Dimensions not needed for standard materials• National standards maintain uniformity


Broken Lengths

• Long parts have portion removed• Reduces drawing space• Dimension not broken• Dimension value reflects complete part


Limits of Size

• General tolerance in notes acceptable• Tolerance on size dimension

– Limit dimensions– Bilateral tolerances– Unilateral tolerances– Single limit tolerances


Limit Dimensions

• Specifies minimum and maximum• Maximum size above minimum• In a note, minimum size before maximum


Plus and Minus Tolerances

• May be bilateral or unilateral• Bilateral tolerance may be equal or unequal


Single Limit Dimensions


Tolerances on Angles

• Limit dimensions• Plus-and-minus tolerances• Orientation tolerances• Single limit not practical


Basic Hole System

• Preferred system• Limits of size for hole calculated first• Typically use standard tool sizes for hole


Basic Shaft System

• May require nonstandard tools for hole• Used when purchasing shaft and mating hole is

specified


Calculating Size Limits Using Standard Tables

• Function of parts considered• Descriptions of general applications provided• Determine class of fit• Determine tolerance values• Tolerance is proportional to size of feature


Running and Sliding Clearance Fits

• Parts move freely• 9 classes of fit

– RC1 through RC9


Location Clearance Fits

• Locating parts without interference • 11 classes of fit

– LC1 through LC11


Location Transition Fits

• Locating parts with slight clearance or interference

• 6 classes of fit– LT1 through LT6


Location Interference Fits

• Locating parts with a press fit (interference)• Not for transmitting loads• 3 classes of fit

– LN1 through LN3


Force Fits

• Locating parts with a press fit (interference)• Bore pressure constant through range• 5 classes of fit

– FN1 through FN5


Limit Calculations Using Tables

• Select a class of fit• Select a category of fit from the class• Find appropriate tolerance table• Locate nominal size in table• Calculate tolerances


Rules in ASME Y14.5

• Rule #1: Perfect form at MMC• Exceptions to Rule #1

– Parts subject to free state variations– Stock materials

• Rule #2: RFS and RMB assumed


Dimension Interpretations


Machine Capability

• Each machine type is uniquely capable• Each machining program for a part is uniquely

capable • Smaller tolerances generally equal larger costs• Know your company and supplier’s capabilities• Machining handbooks provide general

capabilities


Dimension Revision

• Change geometry in CAD• Out-of-scale dimension to be avoided• Reasons for revisions

– Design changes – Corrections– Manufacturing-based changes


Surface Texture Dimensions

• Determined by function• Surface variations

– Roughness– Waviness– Lay

• Roughness width– Roughness width cutoff– Roughness cutoff– Sampling length


Surface Texture Symbols


Explain how a single view can be dimensioned to completely define a cylindrical part.

Create one view that shows both the length and diameter of the cylinder and apply both the length and diameter dimensions to the created view.


List the classes of fit.

Running and sliding clearance, location clearance, location transition, location interference, force fits


Calculate the tolerance for a hole that will accept a purchased shaft with the dimension .5.001, and provide a clearance of min .0012, max .0038 (RC6).

Min hole = .501 + .0012 = .5022

Max hole = .499 + .0038 = .5028

(Max clearance comes from tol table)

hole tol + min clearance + shaft tol


How can an exception to Rule #1 be specified?

Place the independency symbol adjacent to the excepted dimensions to indicate perfect form at MMC is not required.


What is assumed in Rule #2?

Regardless of feature size and regardless of material boundary.


What is the effect of using very small size tolerances on holes?

Smaller tolerances can force the use of more closely controlled manufacturing processes which will increase costs.


Often, what are the only numerical values specified in a surface texture dimension?

Surface roughness and roughness cutoff

4 dimension application and limits of size. gd&t: application and interpretation©...

Documents

dimension application

view slide

circular dimension slide

vertex of angle slide

inch specified slide

limits of size slide

dimension angle

sides of chamfer slide