What are basic cad drafting techniques?
The process of preparing a 2-D drawing varies, depending on the CADD software and preferred design techniques. Software centred on 2-D drafting typically requires you to construct geometry such as lines, circles, and arcs and add dimensions and text. In contrast, to prepare a 2-D drawing when using software or a design process that focuses on building a 3D model, you typically extract 2-D views from the 3-D model. Two-dimensional drawing concepts and theories are the same regardless of the technique used to produce the drawing.
Designing and drafting effectively with a computer requires a skilled CADD operator. To be a proficient CADD user, you must have detailed knowledge of software tools and processes and know when each tool and process is best suited for a specific task. Learn the format, appearance, and proper use of your software’s graphical user interface and customize the GUI according to common tasks and specific applications to increase proficiency. You must also understand and be able to apply design and drafting systems and conventions, plus develop effective methods for managing your work.
Drawing and Editing
CADD software includes commands for creating and modifying all elements of a drawing for any design requirement. Study the CADD drawing in as you explore drawing and editing with a computer. This drawing of a medical instrument part includes straight lines, circles, arcs, text, dimensions, and numerous symbols created accurately and efficiently using a variety of drawing and editing commands. The CADD applications throughout this textbook provide specific information about drawing and editing with CADD.
Line Standards and Layers
CADD programs often include a layer or similar system to organize and assign certain properties to objects. In CADD terminology, layers are elements of the drawing that allow you to separate objects into logical groups for formatting and display purposes. For example, a multi-view mechanical drawing can have layers for each unique line type, Including object lines, hidden lines, dimensions, and section lines (see Figure). You can display all layers to show the complete drawing or hide specific layers to focus on certain items. Lines and Lettering provide detailed information on types of lines. Some CADD systems automatically or semi-automatically set drawing elements on separate layers, and others require that you create your own layering system.
Layers allow you to conform to drawing standards and conventions and help create unique displays, views, and sheets. The following is a list of ways you can use layers to increase productivity and add value to a drawing:
- Assign each layer a unique color, line type, and line weight to correspond to line conventions and to help improve clarity.
- Make changes to layer properties that immediately update all objects drawn on the layer.
- Turn off or freeze selected layers to decrease the amount of information displayed on-screen or to speed screen regeneration.
- Plot each layer in a different color, line type, or line weight, or set a layer not to plot.
- Use separate layers to group-specific information. For example, draw a floor plan using floor plan layers, an electrical plan using electrical layers, and a plumbing plan using plumbing layers.
- Create several sheets from the same drawing file by controlling layer visibility to separate or combine drawing information. For example, use layers to display a floor plan and electrical plan together to send to an electrical contractor or display a floor plan and plumbing plan together to send to a plumbing contractor.
CADD programs often include a layer or similar system to organize and assign certain properties to objects. In CADD terminology, layers are elements of the drawing that allow you to separate objects into logical groups for formatting and display purposes.
For example, a multi-view mechanical drawing can have layers for each unique line type,
Layers Used in Industry
The drawing typically determines the function of each layer. You can create layers for any type of drawing. Draw each object on a layer specific to the object. In mechanical drafting, you usually assign a specific layer to each different type of line or object. The following is an example list of common layers and basic properties assigned to each layer for mechanical drafting applications.
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| Layer Name | Line Type | Line Weight | Color |
| Object | Solid (continuous) | .02 in. (0.6 mm) | Black |
| Hidden | Hidden (dashed) | .01 in. (0.3 mm) | Black |
| Center | Center | .01 in. (0.3 mm) | Green |
| Dimension | Solid (continuous) | .01 in. (0.3 mm) | Red |
| Construction | Solid (continuous | .01 in. (0.3 mm) | Yellow |
| Border | Solid (continuous) | .02 in. (0.6 mm) | Black |
| Phantom | Phantom | .01 in. (0.3 mm) | Magenta |
| Section | Solid (continuous) | .01 in. (0.3 mm) | Brown |
Architectural and civil drawings, for example, can require hundreds of layers, each used to draw a specific item. For example, create full-height floor plan walls on a black A-WALL FULL layer that uses a .02 in. (0.5 mm) solid (continuous) line type. Add plumbing fixtures to a floor plan on a blue P-FLORFIXT layer that uses a .014 in. (0.35 mm) solid (continuous) line type. Draw roadway centerlines on a site plan or map using a green C-ROAD-CNTR layer that uses a .014 in. (0.35 mm) centerline type.
Layer names are usually set according to specific industry or company standards. However, simple or generic drawings may use a more basic naming system. For example, the name Continuous-White indicates a layer assigned a continuous line type and white color. The name is Object-Red, and it identifies a layer for drawing object lines that are assigned the colour red. More complex layer names are appropriate for some applications, including drawing numbers, colour codes, and layer content. For example, the name Dwg101-3Dim refers to drawing DWG101, color 3, for use when adding dimensions. The CAD Layer Guidelines from the American Institute of Architects (AIA), associated with the NCS, specifies a layer naming system for architectural and related drawings. The system uses a highly detailed layer naming process.
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