Engineering 22
This presentation is the property of its rightful owner.
Sponsored Links
1 / 28

Bruce Mayer, PE Licensed Electrical & Mechanical Engineer [email protected] PowerPoint PPT Presentation


  • 65 Views
  • Uploaded on
  • Presentation posted in: General

Engineering 22. GD&T Bonus Tolerance. Bruce Mayer, PE Licensed Electrical & Mechanical Engineer [email protected] Skill-Development Goal. Learn How to Use the GD&T MMC to Avoid Inspection-Rejection of Entirely Functional Parts Use AutoCAD to Construct GD&T Feature Control Frames.

Download Presentation

Bruce Mayer, PE Licensed Electrical & Mechanical Engineer [email protected]

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Bruce mayer pe licensed electrical mechanical engineer bmayer chabotcollege

Engineering 22

GD&TBonus Tolerance

Bruce Mayer, PE

Licensed Electrical & Mechanical [email protected]


Skill development goal

Skill-Development Goal

  • Learn How to Use the GD&T MMC to Avoid Inspection-Rejection of Entirely Functional Parts

  • Use AutoCAD to Construct GD&T Feature Control Frames


Recall matl condition modifiers

Recall Matl Condition Modifiers

  • Maximum Material Condition (MMC)

    • the condition in which a feature of size contains the maximum amount of material everywhere within the stated limits of size.

  • Least Material Condition (LMC)

    • the condition in which a feature of size contains the least amount of material everywhere within the stated limits of size

  • Regardless of Feature Size (RFS)

    • indicates a geometric tolerance applies at whatever size the part is produced

M

L

S


Material condition usage

Material Condition Usage

  • MMC

    • usually when geometric tolerances are applied at MMC the function is assembly

  • LMC

    • function is usually to insure that a minimum distance on a part is maintained

  • RFS – Default Condition

    • often specified to insure symmetrical relationships

    • No “Bonus Tolerance” allowed


Gd t tolerances

GD&T Tolerances

  • From ASME Y14.5M-1994

    • Some ACAD Features based on Y14.5-1982


Mmc bonus tolerance

MMC → Bonus Tolerance

  • Maximum material condition for a HOLE feature is the SMALLEST sized hole.

  • Maximum material condition for a SHAFT feature is the LARGEST shaft.

  • The maximum material condition modifier in a feature control frame means that the tolerance applies at max. material condition.

    • If the actual hole is LARGER than the smallest allowable hole, a BONUS tolerance can be added to the stated tolerance value.


Mmc bonus tolerance example

MMC Bonus Tolerance Example

  • Condsider theGD&T Spec’dPart At Right

  • In particularnote the SIZE,and POSITION TOLERANCE on the Hole

    • Ø = 0.50 ±0.003

    • Ø-POSITION Tolerance = 0.010

      • Relative to BASIC Dims 2.00 & .75

    • MMC Modifier

PositionSymbol


Mmc bonus tolerance cont

MMC Bonus Tolerance cont

  • Then the ToleranceZone at MMCShown at Right

  • The actual center of the hole (axis) must lie in the round tolerance zone. The same tolerance is applied, regardless of the lateral direction.

    • i.e., The Tolerance Zone is Circular, NOT Rectangular

      • Same tolerance at 0°, 45°, 90° Measurement angles


Mmc bonus tolerance cont 2

MMC Bonus Tolerance cont.2

  • Recall The GD&T Spec

This means that the tolerance is .010 if the hole size is the MMC size, or .497. If the hole is bigger, we get a bonus tolerance equal to the difference between the MMC size and the actual size.


Gage fixture design

As the Part Design Engineer We find that Parts that FIT & WORK in the Assembly are Being REJECTED by RI (Receiving Inspection)

Discover that RI does Not Understand “Bonus” Tolerances

To Avoid Scraping Good Parts, Work with a High precision Machine shop to make a Gage Fixture

Gage Pin Precisely Located at (2, 0.75)

Gage Pin Precisely Machined to Ø0.4965

A bit Less than Lo-Lim on Hole-Size;i.e., at the MMC

Gage Fixture Design


Gage fixture design1

Gage Fixture Design

  • Made from Hardened Tool Steel

  • Axis Walls Shifted by the Pythagorean XY distance equal to half the Tolerance Zone


Min hole part checked by gage

Put Small-Hole Part in Gage Block

Min-Hole Part Checked by Gage

  • The Perfect Part Just Fits over the Pin, and Clears the Walls by ½ the Positional Tol.

Zoom In

  • Expand Origin Area


Max hole part checked by gage

Put Large-Hole Part in Gage Block; move it to Up & Rt Till it hits the Gage Pin

Max-Hole Part Checked by Gage

  • Note How the Axis Wall Clearance has Expanded by 0.003

    • Thus the Hole-Ctr for this LMC Part can be Misplaced by 0.008

Zoom In

  • Expand Origin Area


Mmc bonus tolerance1

This means that the tolerance is .010 IF the hole size is at the MMC, or 0.497. If the hole is BIGGER, we get a BONUS tolerance equal to the difference between the MMC size and the actual size.

MMC Bonus Tolerance

NOT to scale

Read Carefully §10-17 thru §10-23 in Text Book

REJECTED – Out of Spec


Gd t caveat use with care

GD&T Caveat → Use with Care

  • GDT is VERY Powerful, BUT…It can be Quite CONFUSING and ESOTERIC

  • Many Degreed Engineers, as well as Most Drafters/Designers (and Some Machinists) have only a Vague Notion About Meaning of GDT Symbols

    • MisApplication and Confusion-Induced Delays are COMMON

      • e.g. Try asking what MMC or RFS means…


Go nogo and go nogo gages

The Gage we Designed is Necessary but NOT sufficient

Go, NoGo, and Go-NoGo Gages

  • However if part DOES Fit, it COULD Still be BAD

    • e.g., If The hole is LARGER than 0.503 it could easily fit the gage

  • Thus our Gage is a NoGo Instrument

  • i.e., if part does NOT fit the Gage, Then REJECT it


Complete go nogo gaging

To Complete the Gage Set, We need to design a Precision Gage-PIN to Test for OverSize Holes

Complete Go-NoGo Gaging

  • This is Also a NoGo Gage

    • If the Pin FITS in the Hole, Then it is REJECTED

  • Thus we have a GO When the Part

    • Fits in the Gage Block (Position & Small Hole)

    • Does NOT Fit the Pin (Large Hole)


Gd t in autocad

Now that We Understand how to USE GD&T let’s APPLY it with ACAD

GD&T In AutoCAD

  • Width now 4.00 ±0.01

  • Height now 1.50 +0.00/-0.02

Time For

Live Demo

  • Let Dim & Tol Our Spacer Plate with Changes


All done for today

All Done for Today

The AMEandBonus Tol.

If a hole, for instance, has the following size and geometric control, and the hole measures .502. It would be incorrect to use a bonus tolerance of .003 (.502 - .499(MMC)) if the hole is not perfectly oriented to the Datums. If the hole is out of perpendicular to datum A by .002, for instance, the bonus that may be used is reduced by that amount. The bonus would be merely .001 and the allowable position tolerance = .016.


Bruce mayer pe licensed electrical mechanical engineer bmayer chabotcollege

Engr/Math/Physics 25

Appendix

Time For

Live Demo

Bruce Mayer, PE

Licensed Electrical & Mechanical [email protected]


Gdt demo 1

Open File

GDT_Demo_Lec-19.dwg_Start.dwg

Set LtScale to 0.5

Set Snap to 0.0625”

Xline at Top Edge

Offset TWICE by 0.5

xLine at Lt Edge

Offset by 0.5

Make Test-Dim to check Text-Height Relative to Part

Text & Arrows at Bit Big

Make DimStyle half_3dec

Scale = 0.5

Precision = 3-decimals

GDT Demo - 1


Gdt demo 2

Change to DimLayer and Dim Thickness at 0.5 offset xline

Use Line to Extend the 0.625 Dim-Ext_ln up to 1.0 offset

Open Geo Tol Dialog Box

Dimension → Tolerance Menus

Use Dialog Box to Spec Flatness & Back Surface as the Datum

GDT Demo - 2


Gdt demo 3

Make DimStyle half_2dec_1side

Dim the 1.50 +0.00/-0.02 Hgt

Make DimStyle half_3dec_Basic

Apply Basic (boxed) Dims

2.000

0.750

GDT Demo - 3


Gdt demo 4

Make DimStyle half_2dec_2sided

Dim 4.00 ±0.01

Make DimStyle half_3dec_2sided_ManualDim Hole Dia.

0.75 Above Top Edge by Offset

Make Feature Control Frame (FCF) using PullDowns: Dimension → Tolerance

Manually position the FCF Below the Ø Symbol

GDT Demo - 4


Gd t result w xlines

GD&T Result w/ xLines


Gd t demo final result

GD&T Demo Final Result


  • Login