lecture7 - Mech 220 Intro to Engineering CAD MECHANICAL...

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Unformatted text preview: Mech 220 Intro to Engineering CAD MECHANICAL DRAWINGS: MECHANICAL DIMENSIONING & TOLERANCING DIMENSIONING 2/3 2/3 FALL 2006-07 Inst.: Charbel Seif Office: Extension: e-mail: Wing B - B-303 3629 cs05@aub.edu.lb Inst. Charbel Seif , Mech 220 02/07/11 1 Mech 220: 7th LECTURE Mech DIMENSIONING: dimensioning a drawing- position dimensioning schemes position DIMENSIONING A DRAWING: position dimensioning schemes Inst. Charbel Seif , Mech 220 02/07/11 2 Mech 220: 7th LECTURE DIMENSIONING DIMENSIONING dimensioning a drawing- position dimensioning schemes position dimensioning x Different dimensioning systems or styles can be used to place or orient dimensions on a drawing based on the: x Dimension tolerance x Space needed for dimensioning x Size of the drawing Depending on the circumstances several or any of the following systems may be used: x Chain Dimensioning x Parallel Dimensioning x Datum Dimensioning x Ordinate Dimensioning x Tabulated Dimensioning x Inst. Charbel Seif , Mech 220 02/07/11 3 Mech 220: 7th LECTURE Mech DIMENSIONING DIMENSIONING drawing dimensioning schemes- (1) chain dimensioning drawing Chain (point to point) dimensioning x x x A string of dimensions placed along a straight line. Every features such as a corner or circle center has an extension line referencing it off. The dimension values are then placed in the chain or straight line form. Inst. Charbel Seif , Mech 220 02/07/11 4 Mech 220: 7th LECTURE Mech DIMENSIONING DIMENSIONING drawing dimensioning schemes- (1) chain dimensioning drawing Chain (point to point) dimensioning Principal advantages: Principal dis-advantages: Inst. Charbel Seif , Mech 220 1) 2) 1) Simple Saves drawing space Appears crowded when small features are used Lousy tolerance stackup 2) 02/07/11 5 Mech 220: 7th LECTURE Mech DIMENSIONING DIMENSIONING drawing dimensioning schemes- (1) chain dimensioning drawing Principal dis-advantages: Lousy tolerance accumulation (stackup) Inst. Charbel Seif , Mech 220 02/07/11 6 Mech 220: 7th LECTURE Mech DIMENSIONING DIMENSIONING drawing dimensioning schemes- (1) chain dimensioning drawing Principal dis-advantages: Possible remedy (yet not a good one): Lousy tolerance accumulation (stackup) x Tolerance decisions are normally made by the design engineer whereas the drafter must place them correctly on the finish drawing according to standards. 02/07/11 Inst. Charbel Seif , Mech 220 7 Mech 220: 7th LECTURE Mech DIMENSIONING DIMENSIONING drawing dimensioning schemes- (1) chain dimensioning drawing Principal dis-advantages: Appears crowded when small features are used. Possible remedies: x It is typical to place an overall dimension above a chained dimension Inst. Charbel Seif , Mech 220 02/07/11 8 Mech 220: 7th LECTURE Mech DIMENSIONING DIMENSIONING drawing dimensioning schemes- (2) parallel dimensioning parallel dimensioning x x Each dimension stands alone, not relying on any other dimension. The inner most dimension is first placed and the other dimensions are staggered starting from the inside and working outward. Inst. Charbel Seif , Mech 220 02/07/11 9 Mech 220: 7th LECTURE Mech DIMENSIONING DIMENSIONING drawing dimensioning schemes- (2) parallel dimensioning Drafting Tip: For clarity, Do NOT stack dimensions symmetrically but rather USE staggered dimensions Inst. Charbel Seif , Mech 220 02/07/11 10 Mech 220: 7th LECTURE Mech DIMENSIONING DIMENSIONING drawing dimensioning schemes- (2) parallel dimensioning parallel dimensioning Principal advantage: Inst. Charbel Seif , Mech 220 Simple since each dimension is independent of other dimensions 02/07/11 11 Mech 220: 7th LECTURE Mech DIMENSIONING DIMENSIONING drawing dimensioning schemes- (2) parallel dimensioning Principal dis-advantage: x Again, lousy tolerances! Splitting the accuracy tolerance on each side becomes a guessing game for the machinist 02/07/11 Inst. Charbel Seif , Mech 220 12 Mech 220: 7th LECTURE Mech DIMENSIONING DIMENSIONING drawing dimensioning schemes- (2) parallel dimensioning (2) Examine Condition C: Possible remedy: x Adding more dimensions to critical spots when more control is needed between the dimensions. 02/07/11 Inst. Charbel Seif , Mech 220 13 Mech 220: 7th LECTURE Mech DIMENSIONING DIMENSIONING drawing dimensioning schemes- (3) datum dimensioning drawing Datum (or BASELINE) dimensioning Setting up a Datum x x It is a precise and controlled system that eliminates tolerance accumulation. The best way to use a datum system pick the longest outside surface. 02/07/11 Inst. Charbel Seif , Mech 220 14 Mech 220: 7th LECTURE Mech DIMENSIONING DIMENSIONING drawing dimensioning schemes- (3) datum dimensioning Dimensioning x x Identify your datum, then place points on the baseline representing the minimum spacing for stacking dimension lines according to standards. Begin dimensioning to the closest feature, then dimension to the next features placing them on the next baseline points 02/07/11 Inst. Charbel Seif , Mech 220 15 Mech 220: 7th LECTURE Mech 220: 7th LECTURE Mech DIMENSIONING DIMENSIONING IMENSIONING drawing dimensioning schemes- (3)3) datum dimensioning rawing dimensioning schemes- ( datum dimensioning Principal advantages: 1) 2) 3) Precise method Reflects how a part is machined ELIMINATES Tolerance accumulation Principal dis-advantage: Takes up too much space Inst. Charbel Seif , Mech 220 02/07/11 16 Mech 220: 7th LECTURE DIMENSIONING drawing dimensioning schemes- (3) datum dimensioning x Chained – Each dimension continues from the previous one. – Tolerances stack – Saves drawing space x Datum – Each dimension is specified from a common baseline. – Tolerances do not stack. – Takes up too much of drawing space Inst. Charbel Seif , Mech 220 02/07/11 17 Mech 220: 7th LECTURE Mech DIMENSIONING DIMENSIONING drawing dimensioning schemes- (4) ordinate dimensioning x x Once the origin is established you can start placing extension lines 1/16” off the feature. Each distance is measured in the X or Y direction and placed at the end of the extension line. 02/07/11 Inst. Charbel Seif , Mech 220 18 Mech 220: 7th LECTURE Mech DIMENSIONING DIMENSIONING drawing dimensioning schemes- (4) ordinate dimensioning drawing Ordinate dimensioning Principal advantages: 1) 2) Saves space by using only one (1) extension line per dimension. Eliminates tolerance stack-up Principal dis-advantage: Potential crowding around fine features Inst. Charbel Seif , Mech 220 02/07/11 19 Mech 220: 7th LECTURE Mech DIMENSIONING DIMENSIONING drawing dimensioning schemes- (4) ordinate dimensioning drawing Principal dis-advantage: Drafting tip: use angled extension lines Potential crowding around fine features Drafting tip: Stagger dimensions Inst. Charbel Seif , Mech 220 02/07/11 20 Mech 220: 7th LECTURE Mech DIMENSIONING DIMENSIONING drawing dimensioning schemes- (5) tabulated dimensions (5) drawing x x x x Is a basic use of the ordinate system. Each Feature is given a symbol that us an alphanumeric code. An origin of the drawing is established. Table or a chart is drawn showing the coordinate of the feature and its dimensions. Inst. Charbel Seif , Mech 220 02/07/11 21 Mech 220: 7th LECTURE Mech DIMENSIONING DIMENSIONING drawing dimensioning schemes- (5) tabulated dimensions (5) drawing Principal advantages: 1) 2) Saves space Eliminates tolerance stack-up Principal dis-advantages: (1) Constantly moving attention from view to dimension table. Inst. Charbel Seif , Mech 220 02/07/11 22 Mech 220: 7th LECTURE Mech DIMENSIONING DIMENSIONING drawing dimensioning schemes- (5) tabulated dimensions (5) Principal dis-advantage: (1) Constantly moving attention from view to dimension table. Drafting tip: use a hybrid ordinate/tabulated scheme Inst. Charbel Seif , Mech 220 02/07/11 23 Mech 220: 7th LECTURE Mech DIMENSIONING: dimensioning a drawing- shape & size dimensioning shape DIMENSIONING A DRAWING: shape & size dimensioning Inst. Charbel Seif , Mech 220 02/07/11 24 Mech 220: 7th LECTURE Mech DIMENSIONING DIMENSIONING dimensioning a drawing- shape & size dimensioning shape x Symbols play a large part in dimensioning different geometrical shapes Inst. Charbel Seif , Mech 220 02/07/11 25 Mech 220: 7th LECTURE Mech DIMENSIONING DIMENSIONING dimensioning a drawing- shape & size dimensioning shape dimensioning Inst. Charbel Seif , Mech 220 02/07/11 26 Mech 220: 7th LECTURE Mech DIMENSIONING DIMENSIONING dimensioning a drawing- shape & size dimensioning shape dimensioning Inst. Charbel Seif , Mech 220 02/07/11 27 Mech 220: 7th LECTURE Mech DIMENSIONING DIMENSIONING dimensioning a drawing- shape & size dimensioning shape dimensioning Inst. Charbel Seif , Mech 220 02/07/11 28 Mech 220: 7th LECTURE Mech DIMENSIONING DIMENSIONING dimensioning a drawing- shape & size dimensioning shape Dimensioning Angles x x In Mechanical Drawings angular units are expressed in x Degrees and decimal parts of a degree. x Degrees and minutes x Degrees minutes and seconds Dimension lines are curved in nature. 02/07/11 Inst. Charbel Seif , Mech 220 29 Mech 220: 7th LECTURE Mech DIMENSIONING DIMENSIONING dimensioning a drawing- shape & size dimensioning shape dimensioning Dimensioning Slopes Using Leader Lines x Slope of an angle may be used instead of an angle dimensioning. 02/07/11 Inst. Charbel Seif , Mech 220 30 Mech 220: 7th LECTURE Mech DIMENSIONING DIMENSIONING dimensioning a drawing- shape & size dimensioning shape dimensioning Dimensioning Circles Leader lines may be used as well to dimension circles x To Dimension a circle, radius or diameter a symbol must be used 02/07/11 Inst. Charbel Seif , Mech 220 31 Mech 220: 7th LECTURE Mech DIMENSIONING DIMENSIONING dimensioning a drawing- shape & size dimensioning shape Dimensioning Circles: R vs. DIA. Inst. Charbel Seif , Mech 220 02/07/11 32 Mech 220: 7th LECTURE Mech DIMENSIONING DIMENSIONING dimensioning a drawing- shape & size dimensioning shape dimensioning Dimensioning Circles Leader lines may be at 30, 45, or 60o Dimensioning Shafts Inst. Charbel Seif , Mech 220 02/07/11 33 Mech 220: 7th LECTURE Mech DIMENSIONING DIMENSIONING dimensioning a drawing- shape & size dimensioning shape Dimensioning Circles Inst. Charbel Seif , Mech 220 02/07/11 34 Mech 220: 7th LECTURE Mech DIMENSIONING DIMENSIONING dimensioning a drawing- shape & size dimensioning shape Dimensioning Circles Inst. Charbel Seif , Mech 220 02/07/11 35 Mech 220: MECHANICAL DRAWINGS MECHANICAL DRAWINGS: the anatomy of a drawing the PLOTTING AREA MATERIAL: MILD STEEL NOTES: 1. DIMENSIONS ARE IN INCHES. 2. OBSERVE TOLERANCES ON MAIN BLOCK UNLESS OTHERWISE SPECIFIED. AUB ENGINEERING GENERAL FITTING PROJECT Inst. Charbel Seif , Mech 220 02/07/11 36 Mech 220: 7th LECTURE DIMENSIONING: Sketching exercise Generate the necessary front and section view of the above model using the top and front views. Inst. Charbel Seif , Mech 220 02/07/11 37 Mech 220: 7th LECTURE Mech DIMENSIONING: DIMENSIONING: Thank you Inst. Charbel Seif , Mech 220 02/07/11 38 ...
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This note was uploaded on 02/07/2011 for the course MECH 220 taught by Professor Charbelseif during the Fall '06 term at American University of Beirut.

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