Power Tip

From CADD Master Ray

Home Grown Parametrics
O.K., so it's a big word. Don't let that fool you. It just means that you want to create a drawing by describing something instead of by drawing it.

For now, CADD's macro and batch capabilities aren't really designed to do this sort of thing by themselves, but with a little help from your spreadsheet software, they can perform incredible feats. The following demonstration might give you some ideas how to implement your own parametric application, to draw whatever it is that you draw, automatically.

As a simple example, suppose that we want to create an application that draws any size rectangle with a circle exactly in the center of it.

Create the following spreadsheet, using any spreadsheet software:

  A B C D E
4 MR;
5 RE, 0 , 0 ;
6   B1 , B2 ;
7 C2, -B1/2 , -B2/2 ;
8   B3 , 0 ;
9 PU;

The notations in italic represent formula, which will vary depending upon your software. Here, B1 indicates column B, row 1.

You will recognize rows 4-9 of the spreadsheet as a CADD batch file. As you change the values which appear after the words Length, Height, and Radius, he values in the batch file below should also change.

Make sure that coumn E is right justified, so that you don't get extra spaces at the end of each line (the batch file won't work with trailing spaces).

Try out some values for these three parameters (that's where the term comes from), and the savet the spreadsheet in two ways: the whole thing in the normal way, and the lower lines (4-9), columns A-E only, as an ASCII file. The method for saving it as an ASCII file will vary with your spreadsheet, but in many cases you can PRINT a certain portion of a spreadsheet to a FILE, instead of a printer. Giv the file the extension .TXT

Now, go to CADD and load the batch file that you have just created. The desired figure will appear at the last point selected, or at the origin if you haven't selected any points.

Any time you need a proportional variation on this figure, just edit the spreadsheet, create a new batch file, and load it into CADD.

You can develop parametric applications to draw column grids, part drawings, details, charts and graphs (this works great!), or anything else that can be described in terms of a specific number geometric similarities and dimensional differences.