Books on Drafting or Technical Drawing

Technical Drawing or Drafting

What is Technical Drawing?

Many references provide a lot of definitions for technical drawing. A technical drawing or drafting is the “academic discipline of creating standardized technical drawings by architects, interior designers, drafters, design engineers, and related professionals.” It is an “integral communication of technical or engineering drawings and is the industrial arts sub-discipline that underlies all involved technical endeavors.¹” It is a “means of clearly and concisely communicating all of the information necessary to transform an idea or a concept into reality.²” It is a “drawing plan, rendered to scale, used to communicate direction and specifics to a group of people creating something.³” It is a “formal and precise way of communicating information about the shape, size, features and precision of physical objects,” a “universal language of engineering used in the design process for solving problems, quickly and accurately visualizing objects, and conducting analysis,” and “a graphical representation of objects and structures.” It is also the “expression of bodies by lines.⁴” It is a “skill, a vocation.⁵” A good technical drawing is “one that properly and conveniently communicates all of the information needed to transform a design into a product that meets or exceeds customer expectations.²”

Technical drawings have many uses in many kinds of applications specially where there is a need for designs and conversion processes, such as those found in manufacturing, engineering, architecture, and construction. Because technical drawings have many uses, there is a need to regulate practices that are involved in creating these drawings. Drafters use standards of practice, of which the most widely used are practices of the US Department of Defense (DOD), the US Military (MIL), the American National Standards Institute (ANSI), and the American Society of Mechanical Engineers (ASME).² Drafters use many geometric figures and symbols to specify the scope and details of a product because it is very important that technical drawings be accurate.³ Drafters create technical drawings using freehand, mechanical, or computer methods.⁴ Processes that are involved in drafting are sometimes time-consuming.¹ One thing that determines the ultimate quality of a product is the quality of its technical drawing. We know if a technical drawing is a good one when developers for a design should no longer need to consult designers or drafters of the drawing because all information that these developers need are already included in the drawing.² In essence, technical drawing is about linear projection.⁵

A Quick Summary of the History of Technical Drawing

Technical drawings are things that are not new. Even during the times of early Greek civilization, technical drawings existed. These drawings were scratched on the floor to guide workers while they were building. As time went on, people learned to use mechanical devices on drafting tables to draft. Nowadays, drafters or designers use computers to aid them in their design works.³ Computers lessened the effort needed by designers to accomplish their tasks. Before the widespread use of drafting software, drafters were required to have an extensive knowledge on the principles of descriptive geometry and to use tools such as t-square, compass, and drafting table. Now, descriptive geometry is no longer used very often because computers do much of the computations. With the use of computers and knowledge in linear algebra, data, such as coordinates of points and their projection on planes, are computed more easily, and designers can now bypass some rules or principles on how to draw correctly.⁵

Methods of Technical Drawing

The three methods in technical drawing are the following:¹

• Sketching
• Manual or by instrument
• Computer-aided design (CAD)

A sketch is a “quickly executed freehand drawing that is not intended as a finished work.” It is a “quick way to record an idea for later use.” Sketches serve as abstractions or summaries of complex patterns or design solutions. Because their purpose is to summarize, sketching results to an enhanced design process. In a way, these sketches aid in the design collaboration.¹

In manual drawing, it is very important to have an accurate drafting table and to give much attention to the positioning of drafting tools. Drafters use a wide array of mechanical instruments and tools, such as compasses and French curves. Drafters of manual drawings are skilled in geometry, trigonometry, and spatial comprehension. They have mastered the mechanics of drawing lines, arcs, and circles, and they are expected to be precise and accurate in giving technical details. One procedure in manual drafting involves using a drafting table with a paper over it, and sliding a T-square across the side of the table over the surface of the paper. Drafters run pencils or technical pens along the edge of the T-square to create parallel lines. Sometimes, the T-square is used to hold other smaller drawing tools, such as squares and triangles. With the use of these smaller drawing tools, drafters could draw lines from different angles. When tasks become repetitive already, drafters use templates, and these templates were made for some specific tasks. Templates are commercially available, but sometimes, drafters prefer to create their own.¹

Manual drawings must be redrawn from scratch when there is a need to modify them. This difficulty was removed by the use of CAD systems. A CAD system is either 2D or 3D. A 2D CAD system is “merely an electronic drawing board.” 2D CAD systems are capable of producing drawings of large projects such as plans for a building or an aircraft, but they do not have the capability to allow designers to test whether components and parts will fit together. These kinds of projects require designers to use 3D CAD software for the modeling, assembling, and checking of components before the actual release of technical drawings to manufacturers.¹

CAD systems, such as AutoCAD, SolidWorks, and Pro/ENGINEER, automate and accelerate the mechanics of drafting tasks. These systems support symbols for common components that are found in many disciplines, such as electrical, electronic, pneumatic, and fluidic. CAD designers follow standards such as those provided by BS and ISO, but, sometimes, it is up to designers to create drawings.¹

¹“Technical drawing.” Wikipedia. 2010. Wikimedia Foundation. 29 July <http://en.wikipedia.org/wiki/Technical_drawing>.
²Goetsch, David L., et al. Technical Drawing. 5th ed. Clifton Park, NY: Thomson Delmar Learning, c2005.
³“Definition of Technical Drawing.” YourDictionary. 20 July 2010. 3 Aug 2010. <http://www.yourdictionary.com/dictionary-articles/Definition-of-Technical-Drawing.html>.
⁴G. Gülsev Uyar Aldas. “JFM210 Technical Drawing and Computer Application Lecture Notes (First Part).” Scribd. 26 Nov 2008. 3 Aug 2010 <http://www.scribd.com/doc/8455804/Technical-Drawing>.
⁵Lee, Xah. “What Is Technical Drawing, Descriptive Geometry, Projective Geometry, Linear Algebra.” XahLee.org. 2 Aug 2010. 3 Aug 2010 <http://xahlee.org/3d/tech_drawing.html>.

Injection Molding is a manufacturing process for producing parts from both thermoplastic and thermosetting plastic materials. Plastic is known to be versatile and economical material that is used in many applications.

Products will be designed by industrial engineers and or an engineer. In modern age, the product can be designed using Computer aided design such as Solidworks, AutoCadd, Pro-E and many CAD softwares.

Design consideration

Always minimize undercut to minimize manufacturing cost. Can use slider if undercut is unavoidable due to its special feature.

Draft. Part design should include draft features to facilitate removal from the mold in direction of the mold opening . Typical draft angles should be 1 to 2 degrees for part surfaces.

Wall Thickness. Use uniform wall thickness throughout the part. This will minimize sinking, warping, residual stresses and improve mold fill and cycle times.

Radii, Fillets and Corners. External and Internal radii should share same center point. A fillet radius should be 25 to 60% of nominal thickness. Break all corners with radius. Suggested minimum radius is 0.5mm (0.020in).

Ribs. Rib thickness should be 50 to 60% of the nominal wall thickness and the maximum height is 3 times the height of the wall.

Boss and Gussets. Typical OD of boss is 2 times ID. It’s height should be less than the 3 times of OD. The height of Gusset can be up to 95% of the boss. While it’s length can be 30 to 100% of its height.

Reference:

http://www.engineersedge.com/injection_molding.htm

http://www.polymerhouse.com/datasheets/GE_Thermo%20Plastic%20%20DesignGuide_[1].pdf

http://en.wikipedia.org/wiki/Injection_molding

http://www.efunda.com/designstandards/plastic_design/plastic_intro.cfm