When Close Isn't Close Enough, Here's the Answer

This month’s workarounds help you draw accurately in isometric, prevent viewports from squaring up on you and quash an academic version plot-stamp infestation

If you use units expressed as fractions, avoid using the dialog box interface to set up your isometric snap and grid. The dialog box will set up the grid and snap spacing inexactly and therefore introduce inaccuracies into your drawings. For example, an isometric line that should be 150.0 degrees may be drawn at 149.97732316 degrees.
Workaround: If you use Ortho mode, at least the angle will be correct. However, you are much better off using the Command-line versions of the Snap and Grid commands, which do not introduce these inaccuracies.

Vexatious Viewports (2000 to 2005 SP1)
If you use nonrectangular viewports, don't freeze their layers. If you do, this appears to work properly at first, but if you regenerate or plot, the viewports lose their clipping and become rectangular. This applies to both normal freezing and viewport freezing.
Workaround. Instead of freezing viewport layers, turn them off or make them nonplotting.

We Don't Need No Education (14 to 2005 SP1)
This isn't a bug in the conventional sense of the word. It's a deliberate designed-in feature. But the way Autodesk has implemented it means that it acts like a virus, passing the infection on from drawing to drawing.

Autodesk makes most of its software available as educational market products, which are sold to students at heavily discounted prices. Use of this software for other than educational purposes is strictly forbidden. To discourage illicit commercial use, AutoCAD plots with an obvious stamp along all four edges of the plot. This applies not only to the educational software, but also to drawings created using that software, even when plotted by commercial versions of AutoCAD. When an educational product drawing is inserted into a normal drawing, the normal drawing inherits the plot stamp.

The problem is that Autodesk's understandable zeal to prevent misuse of its products can sometimes trap companies that would never dream of using illegal software. Consider the following scenario.

A few years ago, a company employed a student for a couple of months. The student took a drawing home and erased a couple of lines in the drawing using his educational version of AutoCAD, before bringing it back to the office the next day. At this point it is worth noting that what the student did was illegal; however, others are about to be punished for the crime.

Some months later, with the student back at college, a coworker opened this drawing, copied a portion of it and pasted it into his own drawing. The portion he copied is nowhere near the lines erased by the student. However, the educational product stamp has now infected the second drawing. On it goes, with the stamp moving around from drawing to drawing and company to company by drawing transmittal, copy and paste, insertion, wblocking and so on. Even copying a single line is enough to pass on the infection. Companies that are several steps removed from the student can be infested with the nasty thing. When the problem is discovered at plot time, it may be impossible to pin down the original source of the problem.

Workaround: Commercial versions of AutoCAD 2004 and 2005 will warn you if you open or insert an infected drawing, allowing you to reject it. A utility is available from ManuSoft that provides a similar warning in AutoCAD 2000, 2000i and 2002.

Of course, that doesn't overcome the possibility that some of your drawings are already infected without your knowledge. What can you do then?

If you are an innocent victim of the plot-stamp infestation, you can apply to your AutoCAD dealer for a special utility, time-limited to 15 days, to fix up your drawings. A DOS utility is also available that you can use to identify the infected drawings. Presumably, if you receive more of these drawings in the future, you need to go on bended knee again for another 15 days of utility use.

It is possibly an apocryphal story that just one person in the depths of Autodesk knows the closely guarded secret rituals of the educational stamp. I have asked Autodesk if a LISP routine exists to detect the presence of the stamp, but have so far been met by a brick wall. I do not understand the rationale behind this secrecy. It makes no sense for two reasons.

First, if a company is silly enough to risk using illegal software, it would more than likely use a cracked version of AutoCAD, which lacks the plot stamp and is even cheaper than the educational version. (At least it's cheaper until Autodesk's antipiracy lawyers catch up with them, at which point it becomes very expensive.)

Second, despite Autodesk's statement that there is no way to circumvent the plot stamp, it is in fact very easy to clean an infected drawing. Anyone who possesses one of these drawings, a modicum of curiosity, and five minutes to spare can work out what can be done to clean it up without any loss of information or precision. I won't describe the method here, but it involves using a command that most people would use every day.

Autodesk has locked and guarded the door to a building, with great restrictions on who is allowed to borrow the key and for how long. Meanwhile, there's a whole wall missing from the side of the building so people can walk in and out as they please.