>I am using extrude, union, intersection, subtract
Those are AutoCAD commands. You can download a free 30-day trial of AutoCAD 2008.
http://usa.autodesk.com/adsk/servlet/mform?id=9106363&siteID=123112
>I am using mdt 2004DX
You might want to go to http://myfeedback.autodesk.com sign up for MDT Beta 2009. Code "Edison" (or was that the code for AutoCAD Mechanical - I can't remember - just search here if that isn't the correct code).
AutoCAD 2009 Beta code "Raptor"
Inventor 2009 Beta code "Tesla"
You can download Inventor LT for free from http://labs.atuodesk.com
Students can download Autodesk Inventor Professional 2008 for free from http://engineersrule.org
-----------------------------------------------------------------------------------------
Autodesk Inventor 2019 Certified Professional
Autodesk AutoCAD 2013 Certified Professional
Certified SolidWorks Professional