What is the best CAD software for patent drawings?

[chason58]

I am looking to buy a CAD software that is:
Unexpensive
Easy to learn
Allows me to make decent patent drawings
It is compatible with most 3D printing machines
Compatible with Windows XP
Thank you in advance for your suggestions

[pascoe69]

Better than inexpensive, have a look on the free CAD programs of the source. It called my attention and I will include on my site of free engineering tools (second source).

[kendell]

Better than inexpensive, have a look on the free CAD programs of the source. It called my attention and I will include on my site of free engineering tools (second source).

I use IntelliCAD. It's a cheaper alternative to the industry standard AutoCAD. It is virtually 100% compatible with AutoCAD and works with the AutoCAD file format, but it is a fraction of the price.
There are several companies making their own IntelliCAD software. After doing some research a few years ago I went for CMS IntelliCAD. I'd recommend it.

For creating diagrams and line drawings the absolute best software I have ever seen is called Autodesk Actrix. For reasons best known to themselves Autodesk stopped selling it about 10 years ago, but if you can get hold of a copy by hook or by crook, do so.

[kennethedward]

IntelliCAD is really good and also easy to use. Microsoft Visio is very common among law firms and some patent illustrators. http://www.patentsusa.com