Working Drawings

Working Drawings

Gaikwad

S. P.

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

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

∙ Tolerances are represented as Direct Limits (A) or as Tolerance Values (B).

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).

Important Terms of Toleranced Parts

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

Important Terms of Toleranced Parts

Allowance – the tightest fit between 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 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)

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.

Functional Dimensioning Functional Dimensioning begins with tolerancing the most important features.

Then, the material around the holes is dimensioned (at a much looser tolerance). Functional features are those that come in contact with other parts, especially moving parts. Holes are usually functional features.

Tolerance Stack-up

Dimensioned from the left.

Occurs when dimensions are taken from opposite directions of separate parts to the same point of an assembly.

AVOID THIS!!!

Dimensioned from the right.

Avoiding Tolerance Stack-up 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.

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 Single Part 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 position 2. 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.

Multiview Sectioned Assembly Drawing of a Spring Pack containing…

Drawing Number

Part Numbers

Pictorial Assemblies

Sectioned Assembly

Pictorial Assemblies

Technical Illustration (Exploded) Assembly

Title Blocks …contain... A. B. C. D.

Name & Address of Company Title of the Drawing Drawing Number 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 Manufacturers J. Drawing Sheet Size K. Actual or estimated weight L. Sheet Number

Parts Lists 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.

Revision

Record any changes Found in upper-right corner Blocks

General tolerance note for inch and millimeter dimensions

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

Tabular Drawings

Fastening Devices 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)

Threaded Fasteners First Application of a screw thread was

developed by Archimedes to lift water. 1800’s Joseph Whitworth – English Standard Screw Threads 1864 – US Screw Thread Standard 1946 – ISO Develops Metric Standard 1948 – US Develops Unified Standard

Standard Thread Notations: Internal Threads Form Chart External Threads

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 and Unfinished hex head bolt is a washer Under 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 screw required for this week’s assembly drawing

Retaining Rings:

Lock Washers:

Pin Types:

Standard Key Types:

Rivets:

Rivets:

Springs:

Create a complete set of Working Drawings