OM Drgs Lectures 4 March 13

8/13/2019 OM Drgs Lectures 4 March 13

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O tomechanical Drawin s:

Geometric Dimensioning & Tolerancing andDrawing Practices

nees maRaytheon Missile Systems

Tucson, AZ

Phone: 520/545-7870 .



Outline

• Geometric Dimensioning & Tolerancing (GD&T) Symbols• Machining Tolerances (meaning, how to specify, ..)• Examples of engineering drawings using GD&T symbols• Drawing Practices

– Format – Numbering – Configuration control

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Geometric Dimensioning &Tolerancing (GD&T)

• What is i t? – A means of dimensioning & tolerancing a drawing using

s an ar sym o s o convey pro uc unc on an es gn

relationship

• ANSI Y14.5 & ISO standards use the same symbols toindicate critical features on a part drawing

• Why use GD&T? – Provides max. production tolerances – Saves money – Ensures design requirements are carried out – Ensures ful l interchangeability of mating parts – Eliminates confusion by using a common international

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engineering language



GD&T Symbols

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GD&T Symbols

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Positional Tolerance

• Specifying tolerance on location of clearance and threaded holes• Hole diameter varies between 0.505” to 0.525”• ax. pos on var a on s ess . a max ma er a con on

(0.525” diameter)

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Machining Tolerances

• Machined part acceptable as long as length, width and holediameter do not vary by more than 0.005’

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Datums and True Positions

• Holes must be positioned accurately relative to top surface andedges ( datums A, B and C)

• om na pos on s n ca e y rue pos on mens ons(enclosed in little rectangles)

• Identical repeating dimensions specified as “n X” – where “n” is

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Engineering Drawings

• Three datums specified (A, B and C)• 4 holes must be located accurately from edges (B & C)

• First hole located 0.50” mm from both ed es

• Other holes centered 1.50” from the first hole

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• Two datums specified (A & B)• 4 threaded and 2 clearance hole must be located accurately from

front surface A and counter bore B

• Flatness of front surface must be within 0.080 mm (80-microns)• Counter bore B must be orthogonal to surface A within 0.1 mm

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• Three datums specified (A, B and C)• Counterbore B is orthogonal to surface A• Circular runout (variation) of thru hole C is controlled relative A & B• Position of 8 thru holes in surface A controlled relative to A & B only

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Profile Tolerance

• Profile (waviness) of curved surface (between edges C & D) is controlled towithin 0.16 mm measured from datums A & B

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Drawing Practices

• Drawin s Format

• Drawing numbering

• Creation and release of drawings

• Steps involved in making changes to released drawings

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Drawing Format Example

• Part name & number, material, finish, heat/chemical treatment• Nest higher assembly• Drawin size scale revision and a roval histor • Default tolerances

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Drawing Numbering

• Information specified in the title block –

the project CM office> First few digits specify the project (top-level product )> Next few di its s ecif the ma or subs stem > Last few digits specify the part

– – Name of the next assembly part belongs to (second l ine) – Size of the drawing & revision level –

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Drawing Release Steps

• Drawing prepared by engineer/designer • Reviewed by engineers from other disciplines (optical,

mechanical, electronics, material, structural, thermal,manufacturing, etc.)

• All changes are redlined and provided to the creator of thedrawing

• Drawing is checked by a checker • Drawin is u dated and released as Rev - Initial Release

– All stakeholders approve the release of drawing• Configuration Management (CM) office vaults an electronic

co of the released drawin in com an database• Electronic copy is available as “ Read Only” to all persons

who have access privileges for that program

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Drawing Changes

• Reason for making changes – Fix drawing errors – incorporate new notes – Design and/or dimensional changes

• Steps involved in changing a drawing – Process initiated by fil ling out a Engineering Change Request

(ECR) form – ECR is reviewed and approved by the affected disciplines – ECR is then presented to the Change Control Board (CCB) – CCB authorizes making the changes to the drawing

– Changes are made to the drawing – Drawing goes thru review and checking cycle – Changed drawing is presented to CCB for final approval

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– Changed drawing is released again as next revis ion level



Configuration Control Boards(CCBs)

• Established by the program manager to approve ordisapprove proposed engineering changes

• CCBs evaluate the need for changes, confirm changeclassifications and effectivi ties, and assure appropriateanalyses of changes and their effects.

• CCBs are chaired by the applicable IPT leader or a notherdelegated person authorized by the program manager.

• CCB membership is based on the contract phase and mayinclude but is not limited to:

a. Program IPT representativeb. Program IPT configuration management representative

c. Operationsd. Engineering

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OM Drgs Lectures 4 March 13