Class 9_2

• Next stage in design process: Testing• Intro to engineering drawing• Computer model assignment due next

Tuesday• Extra office hours Friday morning, 10-

noon.

Questions about DP?

The lab is open.

Define the problem

Specify product requirements

Invent alternatives

Evaluate the alternatives

Engineer the details / analyze performance

Test prototypes

Report complete product description

Model of the Design Process

Testing

• Crucial part of design, because the problems are complex and the solutions not certain

• Often start with simple prototypes• Design the tests carefully so that the results

will be useful• Keep records• Be ready to “iterate”!

Testing

• Testing is not the same as practicing.• Test systematically. • Change one variable at a time, in uniform

steps, hold all other variables constant.• Record the results carefully.

Engineering graphics (technical drawing)

• Technical drawings are an important method of communication among engineers.

• Introduction to the nature and purpose of technical drawings

Nature and purpose of technical drawings

• Technical drawings are formal, not artistic, follow we ll-defined rules/conventions.

• Composed of simple lines, no color, no shading, no vanishing perspective, no extraneous detail, no artistic interpretation.

Nature and purpose of technical drawings

• Primary purpose is to communicate detailed information about the geometry of a design.– Used as a basis for manufacture.– Aid in designing a device by clarifying the geometric

relationships of the parts.– Communicates ideas about the design to others—other

engineers, manufacturer, customer, maintenance staff, parts inventory staff, etc.

– Starting point for other types of analysis, such as FEA stress, etc.

Nature and purpose of technical drawings

• Done by hand (sketches) or with drawing aids (squares, triangles…), or most often today, with the help of a computer (Computer aided drawing, CAD).

Why engineers need to be able to make technical drawing sketches • Helps you develop your ideas and is an aid

to problem solving • Informal communication among colleagues• Quick communication to shop• Communication to drafting staff• Understanding the principles helps

understand formal drawings

Typical “projections”

•  Orthographic projection (sometimes called “multiview” drawings) (the fundamental engineering drawing)

• Isometric projection (a pictorial view)• Oblique projection (another pictorial view)

Stages in making a sketch

• Block-out the outline with “construction lines”• Block-out the major features• Refine shapes• Darken part lines

• Tips: Use construction lines liberally, draw big (use entire page), pay attention to proportions, relax and practice.

Example of the process…

In-class work:

• Use paper provided and a pencil to practice drawing.

• Draw an orthographic projection (three views in proper relationship)

– Start with construction lines to block out all views

– Draw big, keep proportions– Fill in details with heavier lines

Draw an isometric view (single pictorial view)

• Use construction lines• Pay particular attention to proportions• Remember, each front edge at 30 degree

angle

That’s all for today!

Remember: Computer model due Tuesday.