Models are useful when creating drawings for manufacturing. An existing drawing can be used as a template, a starting point. Think of it as a clone, but with legacy data.
Alternatively, starting with a drawing template is equivalent to starting with a blank form.
A conventional drawing model can contain several other nested models. Recent episodes in this column have discussed templates for a sheet format, schedule table, revision table, title block, and general table.
From practical experience, models constantly need to be improved. That is, the models used are faulty but not so faulty; some sets of errors need to be fixed as a routine workflow.
Figure 1 shows a drawing created from a model that has several issues. Other errors and omissions include a wide range of font sizes, an outdated ASME standard (cited in note 2), and a missing third angle projection note. The effort to refine a model is often a call for inaction from a procrastinator.
With the brand of CAD I use, the sheet format is often the source and solution of tedious defects. The sheet format contains the title block, links to custom properties used in the title block, standard notes, and drawing border. The sheet format is fully user definable. It can be completely pristine or completely exotic.
When a drawing file is opened, it loads its designated sheet size. When a drawing is saved, it saves the path to the sheet format it last used. When a drawing is open, the sheet format path can be changed. In Figure 2, the sheet format has been updated to show third angle projection information. This CAD trick of changing the sheet size used is a way to update existing drawings to new company standards.
An existing drawing is powerful in at least two ways:
It can be saved as a copy to create a starting point for another drawing. It can be used to create both a drawing model and a sheet format model to update existing drawings.
As a side note regarding multi-sheet drawings and drawing models, it would be clearer to use the term sheet model instead of drawing model, as separate models are used for the first sheet and subsequent sheets of a multi-sheet drawing . A first sheet format would be used by the first sheet model. Similarly, the nth sheet format would use an nth sheet model.
Compared to using an existing drawing as a starting point, the CAD workflow of saving an existing drawing as a copy to serve as a starting point for a new drawing is particularly appealing when a batch of drawings has more in common than just their drawing standard.
As an example of a CAD project that may involve the drafting of multiple drawings in one batch, we offer the FMA Shop Cart, shown in Figure 3. In addition to conforming to company standards, its initial batch of drawings may share the same revision history—same ECO number, publication date, approval, and author.
Our model design tries to anticipate the workflow of using them. As a result, a CAD sequence of operations might be as follows: use a sheet model as a starting point and refine it to complete a good drawing (with good sheet format, revision table history and updates). up-to-date dates and authors, views, and dimensions).
Save that good first drawing. Then, with the Save As command, create the starting point for the next drawing with a new filename. This new drawing file is slightly dangerous. It has a meaningful name but presents the old 3D model (as a component in the view).
To fix this unsafe drawing, open it and use the Replace Model command to update the displayed model (in all views). The result of replacing the model will likely be dangling dimensions and possibly outdated views. The good news is that redundant data entry is reduced.
As an alternative workflow to Replace Model, a button called References that appears in the CAD system file open dialog can be used. Clicking the References button changes the referenced components that the drawing file opens. This allows Windows Explorer to be used to make a copy of the correct file and then change references when opening that copy.
If all goes well, the views of the new drawing now show the correct model. The main task is to update the dimensions in the views. Data entry for revision history and authorship is legacy and saves time.
Pack&Go is an alternative to Save-As. Pack&Go eliminates the need to replace the model. When only one file name needs to be changed for the new drawing, Save As or Replace Model is an efficient workflow.
If several filenames need to change during model creation, then Pack&Go is the efficient tool. Its user interface is table-oriented with useful tools for editing the data displayed in table cells.
Going back to the CAD trick of creating sheet models from drawings, the models shine without the inherited clutter of outdated dimensions and incorrect views. The Save Sheet Format command creates a file that can be used by other existing drawings, including existing sheet models. This is a way to update the sheet format of these drawings to current company standards.