If you want to screw around doing purely artwork, you can use Maya. If you want to do legitimate mechanical design, use a legitimate CAD program.
I've used Solidworks, Inventor, and Pro/E Wildfire, and Catia V5.
Solidworks or Inventor are by far the way to go. They are VERY similar in capability and price. Very powerful, super easy to use. Much easier I think to get started in than Pro/E or Catia. Catia has historically had better complex surfacing tools, but Solidworks has been closing the gap rapidly.
An example of Solidworks?
http://www.dexigner.com/detail/files/12646.jpg
If you're a student you'll be able to pick up a student license of SW on the cheap. Otherwise, commercial license is a few grand. Cheap compared to $30-45,000 for Catia.
Grip is a four letter word. All opinions are my own and not those of current or previous employers.