CAD Mechanical 1

Principles of Design

The over arching purpose of the CAD Mechanical course is to help students to develop the basics and principles of the industrial designer, CAD technician, engineering technician, or other related career. Because of this concept we are asking to the students to perform at professional levels and model the practices that would be required at a firm. This means to they need to work on those 21st century skills which include responsibility, civility, and personal pride in themselves. This follows our school resilience program and also our Ah, CV program.

Resilience at our school is a program that we as a school are engaged into help all of our students develop those skills needed to overcome and succeed in challenging and difficult situations. These may be school, personal, or professional situations. This is our response to the needs of the students in our society today. Students are bombarded with more and more activities and expectations. We, as a school, hope that all of our students will find success in their endeavors and activities. To do this they need to understand and have the abilities to deal with failures, challenges, and hardships as they encounter them.

Ah, CV! is a student response and intervention program. Students are expected to hold themselves "Accountable" for their actions, decisions, responses, and all that they do. They will be "Civil" to others and demand through their own actions that others are civil to those around them as well. This will include being an active and respectful citizen, demonstrating courtesy to others, and embracing others that do not share the same perspectives. Also students will be have "Valor" and demonstrate courage. This will be through Their actions towards others. Making those choices that may not be easy but are honorable and thoughtful.

Standards: ASME

The organization American Society of Mechanical Engineers (ASME) controls the current acceptable standards for the United States engineering community. This organization collects and publishes the documents that are used industry wide to ensure that various firms and companies are following the same standards for clear and concise communication. The drafting standards are included in a document referred to as Y14.5 M

The Y14.5 standard is considered the authoritative guideline for the design language of geometric dimensioning and tolerancing (GD&T.) ... GD&T is an essential tool for communicating design intent — that parts from technical drawings have the desired form, fit, function and interchangeability.

Technical Sketching

Sketching is the most basic way of taking the ideas we conceive in our mind and communicating them visually, by drawing them on paper. Think of a time when you tried to explain an idea for a new invention, or directions to a specific place, and the person you were talking to could not fully understand. You most likely grabbed a piece of paper and made a freehand sketch of what you were trying to verbally communicate. Though not a perfect technical drawing, it was the sketch that brought understanding to your idea. As a technical designer, you will be asked to explain your ideas in a simple way in order to communicate with others. The five characteristics of a good sketch are: neatness, uniformity, stability, proper spacing, and speed. Sketching, therefore, is one of the most critical skills you will learn as a designer. When a sketch is complete, the designer will take the sketch and transfer the idea to a CAD drawing, which will then be used to manufacture the part

The three basic sketching tools are: pencils, eraser and paper. mechanical pencil is the most functional type to use in sketching, but any writing tool will work. The type of eraser used is the preference of the designer. The type of paper used is also the decision of the designer. However, using graph paper will help the designer to draw straight lines and proper proportion of the object.

Lettering

The most common font used in technical design is single-stroke Gothic. It is easy to draw and read. Lettering on a technical drawing is always done with upper-case letters. Although CAD programs can be used to make precise lettering, it is important to be able to hand letter the sketches that are produced.

Lines of different types (line type) and line thickness (line weight) are used in technical drawings to communicate, with the least amount of confusion, the graphics of a project. These include, the objects shape, features, dimensions, etc. The various lines used in a drawing are called line types. The use of line types in a drawing are used to describe the various features of an object to the person reading the print.

A line is the most fundamental and perhaps the most important, single entity on a technical drawing. Construction lines are usually the first lines that are used when laying out a drawing. They are guide lines that help the designer organize the placement of different features on the paper. Construction lines should be drawn very lightly as they will be erased after the final lines are drawn. Object (visible) lines help to illustrate and describe the shape of objects that will later become real parts. Hidden lines are used to show features in an object that are not visible from a viewer’s point of view. Centerlines are used as location markers for the center of circles or arcs, and to show the symmetry of an object. They are also used to indicate multiple objects that are aligned with each other; multiple holes, etc. These four line types, construction, object, hidden and center lines, are the most common line types used in sketching.

There is a rule called precedence of lines that governs how lines relate with each other in a technical drawing. The rule is used when one line type overlaps another line type. To satisfy this rule, a continuous object line takes precedence, and therefore, covers up hidden and center lines. Hidden lines take precedence over centerlines. Cutting plane lines take precedence over any lines. illustrates how lines are used in a technical drawing. The other line types in the figure below will be used and explained in future sections.

Line weight refers to the thickness of a line. The lines of a sketch are usually all the same thickness, because the designer will make a quick sketch using only one marking device. When designing in CAD, the line weight varies to create contrast within the drawing. Regardless of the width of a line, or type of line, it should always be as dark as possible in the final sketch.

Orthographic Projection

How important is visualization and communication to the world of engineering and technical design?

Different types of views communicate different types of information. An isometric view is a specific method of projecting the view of a particular part or object. The isometric view is considered to be a pictorial view of a part or object. This means that the features located on the Front, Right Side, and Top Plane, as shown in preceding image, may not be true to their size and or shape. If the features are not represented as true size, length, or shape, it would be a poor method of communicating that critical information to someone trying to make (fabricate/produce) the part to an exact dimension (size). The information that the isometric view does communicate is an overall idea of what the part or object looks like in just one view. The projection or orientation of the part in an isometric view allows the viewer to see the features on the Front, Right Side, and Top view, all in one view. To help the visualization of the part or object, isometric views are often shaded. The Front and Right Side surfaces are rotated 30 degrees from the horizontal. The Isometric Grid in the background is used to help maintain the 30 degrees and verify the length of the part in all three directions (width, depth, and height). In this part of the module, you will learn to recognize an isometric view as well as how to sketch basic parts using the Isometric View.

Orthographic projection is a method of describing what an object looks like from several different views. Orthographic views are also called engineering drawings or plan views. Using a set of orthographic planes, an illustrator can easily draw the three-dimensional object from any angle and in perspective, isometric or any number of other drawing systems. 3D modelers often use orthographic views to accurately create an object in a 3D application.

Basically orthographic projection is a method to describe a three dimensional object in two dimensional space. Typically an orthographic projection will have the top, side and front views of an object drawn together with some kind of scale and at 90˚ from one view to another. This is where the name comes from, “ortho” means “at right angle”.

Light construction lines are used to transfer information from one view to another. This eliminates the need to re-measure size or location of features in an object. In orthographic projection a miter line is used to transfer information from the top view to the right side view, with the miter line always drawn at 45˚ see the figure to the right. When a construction line crosses the miter line; the line changes direction towards either right or left side view, projecting the geometric information from the previous view.

Orthographic projection allows for the use of dimensions to be applied to the object. ASME designations for these dimensions are as follows:

Height is the vertical measurement between two or more surfaces or lines.
Width is the horizontal distance between surfaces.
Depth is the front to back measurement between the surfaces or lines.

Dimensions

en.wikipedia.org/wiki/Geometric_dimensioning_and_tolerancing

To the left is a link to Wikipedia's GD & T page. This would be the best resources to assist you in understanding the practice as applied in engineering drawings and design. Also refer to our classroom discussions and YouTube channel.

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