Working Drawings

S. P. Gaikwad

First, here’s what we talked about last time…

Applying Tolerances

∙ Tolerances are represented as Direct Limits (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

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 oftolerances (written in decimals).

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.

Important Terms of Toleranced Parts

Allowance – the tightest fitbetween two mating parts.

(The minimum clearance or maximum interference).

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.

Important Terms of Toleranced Parts

Piece toleranceThe 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)

Fit Types:

A Clearance Fit occurs when two toleranced mating parts willalways leave a space or clearance when assembled.

An Interference Fit occurs when two toleranced mating parts willalways interfere when assembled.

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 isdimensioned (at a much looser tolerance).

Tolerance Stack-upOccurs when dimensions are takenfrom opposite directions of separateparts to the same point of an assembly.

Dimensionedfrom the

left.

Dimensionedfrom theright.

AVOID THIS!!!

Tolerance stack-up canbe eliminated by carefulconsideration and placement of dimensions.(Dimension from same side).

Better still, relate the twoholes directly to each other,not to either side of the part.The result will be the besttolerance possible of ±0.005.

AvoidingToleranceStack-up

Today’s Lecture - Week 10:Working Drawings

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.

A Detail Drawing of a SinglePart Called a Lever

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

Detail Drawing of the retainer ring used to fasten the rod to the piston.

Drawing Number

Part Numbers

Multiview Sectioned AssemblyDrawing of a Spring Pack containing…

Pictorial Assemblies

Sectioned Assembly

Pictorial Assemblies

Technical Illustration (Exploded) Assembly

Title Blocks

A. Name & Address of CompanyB. Title of the DrawingC. Drawing NumberD. Names and dates of drafters,

checker, issue date ,contract number, etc.

E. Design ApprovalF. Additional Approval BlockG. Drawing Scale H. Federal Supply Code for

ManufacturersJ. Drawing Sheet SizeK. Actual or estimated weightL. Sheet Number

…contain...

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

Revision BlocksRecord any changes - Found in upper-right corner

General tolerance note for inch and millimeter

dimensions

ANSI drawing sheets with “zones” located on the

border.

Tabular Drawings

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

Mechanical Fastening –Process that uses manufactured devices (Nuts and Bolts)

Bonding – Using material (Glue, Welding)Forming – Using component shape itself

(HVAC, Tupperware, Velcro)

Fastening Devices

Threaded FastenersFirst Application of a screw thread was

developed by Archimedes to lift water.1800’s Joseph Whitworth – English Standard

Screw Threads1864 – US Screw Thread Standard1946 – ISO Develops Metric Standard1948 – US Develops Unified Standard

Standard Thread Notations:

Internal Threads

External Threads

Form Chart

Specifying Tap Drill Size:

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

Thread Representation:

General Types of Fasteners:

Finished vs.Unfinished Bolts:

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

Nuts:

Cap Screws:

Notice the chamfer (Also found on bolts).

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.

Set Screws:

Shoulder Screw:

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

Retaining Rings:

Lock Washers:

Pin Types:

Standard Key Types:

Rivets:

Rivets:

Springs:

Create a complete setof Working Drawings