The following are links explaining first and third angle projections:
 

• http://tpub.com/content/engineering/14069/css/14069_156.htm
• http://en.wikipedia.org/wiki/Orthographic_projection
• http://www.technologystudent.com/designpro/ortho1.htm
• http://www.technologystudent.com/designpro/ortho2.htm

 
• Direct Gear Design for Spur and Helical Involute Gears
• Drawing an Approximate Representation of an Involute Spur Gear Tooth
• The Involute Curve, Drafting a Gear in CAD and Applications