2.3 WORKING DRAWINGS

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The basic skills/topics discussed below lead up to preparing, and understanding a complete set of drawings.

The purpose of working drawings is to,

- describe the exact geometry of parts

- indicate other details associated with drawings (for example, material)

- show how parts are assembled

- indicate manufacturing preferences

generally, the drawing package will include a number of items,

- a drawing (one a separate sheet with a separate title block) for each part

- a bill of materials

- an assembly drawing

a typical working drawing package will contain,

- a design layout

- assembly drawings (and a Bill of Materials)

- subassembly drawings

- detailed drawing

- purchased parts

- modified purchased parts

2.3.1 Drawing Elements

2.3.1.1 - Title Blocks

Most of the important details are put in this block. Each block is individualized to a company, but generally they include,

- company name, and division if applicable

- machine or department name

- part name

- drawing number

- part number

- the number of parts required

- the scale

- drafter name/date

- drawing checker name/date

- material

- tolerances

- finishing details

- units of drawing

The block is typically located in the bottom right hand corner of the drawing

The drawing title, and drawing number are commonly printed in large fonts

2.3.1.2 - Drawing Checking

this is a process whereby a drawing is reviewed for completeness, accuracy, etc.

modern CAD systems, especially solid modeler should reduce the emphasis on checking the drawings. Some of the main features checked for in manual drawings are,

- appearance - this can be a large issue for hand drawn work

- within standards - legal and corporate

- clarity - all description, dimensions, etc should be well understood

- completeness - sufficient dimensions, etc should be present for production

- redundancy - redundant information should be eliminated unless essential

- manufacturability - the cost and feasibility of production should be considered. are tolerances sufficient/excessive, are other steps sufficient for product life.

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2.3.1.3 - Drawing Revisions

When a drawing has reached production, it is considered final, but changes are frequently made.

It is very important that drawing changes are dealt with properly. This means,

- all changes are recorded on the drawing, and new drawings made

- all old drawing must be collected, or marked void (failure to do this can lead to very expensive mistakes)

- when a drawing has been changed a number of times, it should be redrafted.

Computer CAD systems still do not sufficiently deal with problems such as these, and often rely on the previous manual drafting systems to process these updates. But, software is available, and is being developed for product information management (PIM) that will deal with these changes in a manner suitable for CAD.

2.3.1.4 - Bill of Materials (BOM)

An important list on most drawings is a Bill of Materials, this is a list of all required materials/parts required to make to part depicted in the drawing.

This list contains,

- all part numbers

- all part names

- quantity of parts required

- materials required

- source

This is sometimes given on separate sheets, or on the drawing itself

The typical (but not the only) order for listing parts on a BOM is,

1. produced in-house

2. specialty purchase (e.g. roller bearings)

3. standard purchased hardware (e.g., washers)

4. bulk items (e.g. lubricants)

2.3.2 Drawing Types

2.3.2.1 - Assembly Drawings

These are used to specify an assembly with,

- a drawing of the assembled part

Hidden lines are typically omitted from these drawings. Details may also be omitted if they have no bearing on the product

assembly instructions may also be included in these drawings to guide workers

full section assembly drawings are often used

dimensions not included unless essential

Small blow-up bubbles are often used to emphasize details

The parts can be identified using,

- numbers with arrows and a block list of parts including,

- quantity

- part name

- part source

- part number

- reference number

- drawing number

- arrows and descriptions

- quantity

- part name

- part source

- part number

- drawing number

2.3.2.2 - Subassembly Drawings

these are basically the same as assembly drawings, except that there are components that have already been assembled.

Modern equipment is complex and is assembled in stages. The final assembly might be something like an automotive body welding shop, whereas a sub-assembly might be the car radio.

2.3.2.3 - Exploded Assembly Drawings

these are drawings that show each piece separated, and indicates their assembly paths. This can help when determining,

- which part goes where

- the orientation of the part

- the part of approach

- the order of assembly

2.3.2.4 - Detailed Drawings

These drawings use the techniques discussed earlier in this section to depict, and dimension parts.

************************* INCLUDE A COMPLETE DRAWING PACKAGE TO ILLUSTRATE