How to reuse CAD content and symbols
One of the most productive features of CADD is the ability to reuse drawing content that is, all of the objects, settings, and other elements that make up a drawing. Drawing contents such as objects and object properties, text and dimension settings, drafting symbols, sheets, and typical drawing details are often duplicated in many different drawings. The most basic method of reusing content is to apply commands such as MOVE, COPY, and ROTATE; these allow you to modify or reuse existing objects instead of re-creating or developing new objects.
File templates, described later in this chapter, are another way to reuse drawing content. Customized templates provide an effective way to start each new file using standard settings. Another method to reuse drawing content is to seek out data from existing files. This is a common requirement when developing related drawings for a specific project or working on similar projects. Sharing drawing content is also common when revising drawings and when duplicating standards used by a consultant, vendor, or client. Most CADD programs provide several other options that automate the process of sharing drawing content, including reusing pre-drawn symbols and entire drawings. Specific CADD applications throughout this textbook provide additional information about reusing content with CADD.
The ability to create and store symbols in a drawing for future use is a major benefit to drawing with CADD. Saved reusable symbols are known by names such as symbols, blocks, cells, and reference files, depending on the CADD software. You can insert symbols as often as needed and share symbols between drawings. You also often have the option to scale, rotate, and adjust symbols to meet specific drawing requirements. Using symbols saves time in drawing creation and increases productivity.
Draw the elements of a symbol as you would any other geometry. A symbol can usually consist of any object or group of objects, including annotation, or it can be an entire drawing. Review each drawing and project to identify items you can use more than once. Screws, punches, subassemblies, plumbing fixtures, and appliances are examples of items to consider converting to reusable symbols. The process of converting objects to symbols varies with each CADD software. The common requirements are to select the objects to define as the symbol, specify an insertion base point that determines where the symbol is positioned during insertion, and save the symbol using a unique descriptive name. The figure shows some common drafting symbols. Once you create a symbol, the symbol is ready to insert in the current file or be added to other files as needed. As you define symbols, prepare a symbols library in which each symbol is available for reference. A symbol library is a collection of symbols that can be used on any drawing.
CADD software usually provides additional ways to reuse content, such as a system for referencing existing files. For example, AutoCAD provides an external reference, or Xref, the system to automate and manage file referencing. File- referencing tools provide an effective way to use and relate existing base drawings, complex symbols, images, and details to other drawings. File referencing also helps multiple users share content. Whether you have the option to reference a variety of files depends on the CADD software. For example, AutoCAD allows you to reference a drawing (DWG), design web format (DWF and, DWFx) raster image, digital negative (DNG), or portable document format (PDF) file. Referencing a file is similar to inserting an entire drawing or a portion of a drawing as a symbol. However, unlike a symbol, which usually stores in the file in which you insert the symbol, reference file information does not add to the host drawing. File data appears on-screen for reference only. The result is useful information but with a much smaller host file size than if you inserted a symbol or copied and pasted objects. Another benefit of file referencing is the link between reference and host files. Any changes you make to reference files update in host drawings to display the most recent reference content. This allows you or a design drafting team to work on a multi-file project with the assurance that any revisions to reference files display in host drawings.