I have earlier posted about soldering irons. Here is a continuation to it with a set of interesting soldering iron tear-down and DIY videos from YouTube.
Inside the cheapest soldering iron on ebay.
How To Make a MINI USB Power Soldering Iron
Hot! Hot! Hot! Weller ROBUST Soldering Gun, BEB #21
Homemade Soldering Gun
How To make Powerful Soldering Gun