precision matters >> A look at design in the metal fabricating world
Gerald Davis is a job shop consultant and chairman of the board of DSM Manufacturing Co.
Putting 3-D CAD on the grill, Part V
The next lesson in top-down design: Document management
ur design project has captured the overall inspiration for the Shashlik Grill
(see Figure 1). We have many of the major components modeled paramet-
rically, but we still have several features to invent and model.
What’s in a Name?
The main tool we use for storage and organization is the operating system—
Windows®, in most cases. Every operating
system I’ve encountered stores documents
as files and folders. The combination of
drive letter and nested chain of folders is
often referred to as a path.
When it comes to naming, I’m of the
opinion that shorter is better. File names get
typed into fields in forms, and long file names
and paths generally become a nuisance.
People-friendly Folders
Folders are easy to create and provide a reasonably good way to separate one project
from another. I’m keeping most of the files
for the grill in a folder called Shashlik Grill.
I frequently create subfolders that capture
the revision of a project as it moves
through the design evolution. These subfolders are named Rev A, Rev B, and so on.
The date of revision sometimes ends up
being important as well. The operating system does a fine job of putting dates of creation on the folders. However, when the
folder gets copied onto a new drive, the
date of original creation can get lost.
When I’m naming a project subfolder, I
frequently include both a revision and a
date—something like Rev A 06-30-2010.
That way, when it gets zipped up for archiving, it is easier to interpret when the design
work was done rather than simply when
the operating system created the files.
CAD-friendly Files
My rationale for naming files is slightly different from that used for naming folders. I
want my folder names to be pretty easy to
interpret by humans. I want my file names
to benefit the vagaries of the 3-D CAD
software that I’m using.
We could name a file Shashlik Grill
Lower Pan FMA-SG-0100 REV A.sldprt, but
I don’t do that for two reasons:
Enter reader service code 465510 at www.ffid.net
1. It is too long.
2. Including the revision in the file name
will unnecessarily complicate the CAD model
editing process.
Why File
Names Matter
The 3-D CAD software
I use features three
distinct types of files—parts, assemblies, and drawings. Parts are
grouped together into assemblies. Parts or assemblies are referred to as
components. Drawings are the 2-D representations of components. When the software
opens a drawing, the drawing file has a pointer that identifies which component file to
use when displaying the drawing.
If my CAD file for the component has a revision in its file name, and if I change that
revision, then I also have to update the pointer in the drawing file to let it know that it
now has to look for a different component file.
Similarly, an assembly file is also a collection of pointers to other components. If the
file names for the components are changed without keeping those pointers up-to-date,
the assembly file will be corrupted.
One or two work flow procedures within the CAD system make the process of
changing component names relatively painless. However, changing file names within
the operating system in certain ways will aggravate the CAD system. From experience,
my best practice is to minimize the need for renaming files.
It is worth noting that the entire path is used in these pointers to components, so
moving a file to a different drive, changing a folder name, or renaming a part file can all
cause the CAD system to lose its mind, so to speak.
In general, if you need to rename or relocate a file, do so using tools and procedures
provided with or recommended by the CAD system. Be very careful about simply using
Windows to rename or reorganize files and folders. I’ve heard CAD jockeys use harsh language because of busted file pointers.
Figure 1 This
rough sketch shows
the completed Shashlik Grill.
File Properties
File properties can let you have short file names and still have happy people.
All Windows documents have file properties. A file property has two elements—a
name and a value. The author of a document has the option of using the file properties—
creating them or referring to them is entirely optional as far as Windows is concerned.
The CAD software I’m using makes a small improvement to Windows Explorer. If
file properties Description and Revision are defined, then their values will be displayed
by Windows Explorer when the mouse is hovered over the file name. That way, people
can see a lot of detail without packing it all into a long and hard-to-manage file name.
The same CAD software also employs file properties to fill in title blocks on drawings and to populate columns in bills of materials. Data such as source, cost, manufacturing process, material, and so forth, can all be entered into file properties.
Prognostication
In Part VI of this series, we’ll test some of the parametric features of our design by stretching the shape for better material utilization as well as better shipping container size.
Keep in mind that this top-down modeling technique we’re using is not the only
way to do this work. It may not even be the best way in every situation. However, when
it comes to virtual prototyping, it is efficient to use parametrically driven features. It
takes some time to set up initially, but it will pay off later by speeding the revision
process. The use of reference geometry to control parametric features reduces the complexity of figuring out what drives what.
Gerald Davis uses CAD software to design and develop products for his clients at
www.glddesigns.com.
You are not alone, and the problems you face often are shared by others. Share the grief,
and perhaps we will all share in the joy of finding answers. Please send your questions
and comments to dand@thefabricator.com.
