18002757 working drawings

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Working Drawings 

S. P. Gaikwad

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First, here’s what we talked about

last time… 

 Applying Tolerances

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∙ Tolerances are represented

as Direct Lim its  (A) or as

Tolerance Values  (B).

Representing Tolerance Values ∙ Tolerance is the total amount a

dimension may vary and is the

difference between the maximum

and minimum limits.

(A) Tolerance = .04

(B) Tolerance = .006

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Important Terms of Toleranced Parts 

 A System is two or more mating parts.

Nominal Size is used to describe the general size (usually in fractions).

Basic Size  – theoretical size used as a starting point for the application of

tolerances (written in decimals).

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Important Terms of Toleranced Parts 

Limits – the maximum and minimum sizes shown by the tolerance dimension.

The large value on each part is the Upper Limit , the small value = Lower Limit .

 Actual Size is the measured size of the finished part after machining.

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Important Terms of Toleranced Parts 

 Allowance  – the tightest fit

between two mating parts.

(The minimum clearance or maximum interference ).

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Important Terms of Toleranced Parts 

Maximum Material Condition (MMC)

The condition of a part when it contains

the greatest amount of material. 

Least Material Condition (LMC)

The condition of a part when it contains

he least amount of material possible. 

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Important Terms of Toleranced Parts Piece tolerance 

The difference between the upper and lower limits of a single part

(.002 on the insert in this example, .004 on the slot.).

System tolerance

The sum of all the piece tolerances.

For this example (.006)

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Fit Types:

 A Clearance Fit occurs when two toleranced mating parts will

always leave a space or clearance when assembled.

 An Interference Fit occurs when two toleranced mating parts will

always interfere when assembled.

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Functional Dimensioning  

Functional features are those that come in contact with other parts,

especially moving parts. Holes are usually functional features.

Functional Dimensioning  begins with tolerancing the most important features.

Then, the material around the holes is

dimensioned (at a much looser tolerance).

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Tolerance Stack-up  Occurs when dimensions are taken

from opposite directions of separate

 parts to the same point of an assembly.

Dimensioned

from the

left.

Dimensioned

from the

right.

AVOID THIS!!!

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Tolerance stack-up can

be eliminated by careful

consideration and

 placement of dimensions.

(Dimension from same side).

Better still, relate the two

holes directly to each other,

not to either side of the part.

The result will be the best

tolerance possible of ±0.005.

 Avoiding

Tolerance

Stack-up 

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Today’s Lecture - Week 10:

Working Draw ings  Generally, a complete set of Working Drawings for an

assembly includes:1.) Detail Drawings of each non-standard part.

2.) An Assembly or Subassembly drawing showing

all the standard parts in a single drawing.

3.) A Bill of Materials (BOM).

4. A Title Block.

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 A Detail Drawing of a Single

Part Called a Lever  

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 Assembly Drawing of a Piston & Rod containing 8 parts.

 An assembly drawing normally consists of the following:1. All parts drawn in their operating position2. A parts list or Bill of Materials (BOM)

3.Leader lines with balloons indicating all parts.4. Machining and assembly instructions

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Detail Drawing of the retainer ring used to fasten the

rod to the piston.

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Drawing Numb

Part Numbers

Multiview Sectioned Assembly

Drawing of a Spring Pack containing… 

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Pictorial Assemblies

Sectioned Assembly

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Pictorial Assemblies

Technical Illustration (Exploded) Assembly

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Title Blocks

 A. Name & Address of Company

B. Title of the Drawing

C. Drawing Number

D. Names and dates of drafters,

checker, issue date ,contract number, etc.

E. Design Approval

F. Additional Approval Block

G. Drawing Scale

H. Federal Supply Code for

ManufacturersJ. Drawing Sheet Size

K. Actual or estimated weight

L. Sheet Number

…contain... 

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The information normally included in a parts list is as follows:

1. Name of the part.

2. A detail number for the part in the assembly.

3. The part material, such as cast iron or bronze.

4. The number of times that part is used in the assembly.

5. The company assigned part number.

6. Other information, such as weight, stock size, etc.

Parts Lists

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Revision BlocksRecord any changes -

Found in upper-right corner

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General tolerance note for inchand millimeter dimensions

S

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 ANSI drawing sheets with“zones” located on the border. 

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Tabular Drawings

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Fastening is a method of connecting or joining two ormore parts together, using devices or processes.

 Mechanical Fastening–

Process that uses manufactureddevices (Nuts and Bolts)

Bonding – Using material (Glue, Welding)

Forming – Using component shape itself (HVAC,

Tupperware, Velcro)

Fastening Devices  

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Threaded Fasteners First Application of a screw thread was developed by

 Archimedes to lift water.

1800’s Joseph Whitworth – English Standard ScrewThreads

1864 – US Screw Thread Standard

1946 – ISO Develops Metric Standard

1948 – US Develops Unified Standard

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Standard Thread Notations:

Internal Threads

External Threads

Form Chart

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Specifying Tap Drill Size:

 A Tap is a tool used to make threads in holes. A Die is used to make external threads.

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Thread Representation:

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General Types of Fasteners:

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Finished vs.

Unfinished Bolts:

The difference between a finished andUnfinished hex head bolt is a washerUnder the head of the finished bolt.

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Nuts:

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Cap Screws:

Notice the chamfer (Also found on bolts).

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Machine Screws:

Machine Screws are finished with flat bottoms instead of chamfered corners.

 A ½” Hex Head Machine Screw is used on this week’s assembly drawing. 

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Set Screws:

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Shoulder Screw:

Check Appendix 33 for the dimensions of the shoulder screwrequired for this week’s assembly drawing 

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Retaining Rings:

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Lock Washers:

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Pin Types:

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Standard Key Types:

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Rivets:

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Rivets:

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Springs:

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Create a complete setof Working Drawings