Here are some some interesting articles and videos about wooden planes and double irons.

The famous Kato-Kawai video that sparked the modern revival of the double iron:
http://vimeo.com/158558759

An article on how to set a cap iron by David Weaver:
http://www.woodcentral.com/articles/test/articles_935.shtml

Here's a concise video on setting a cap iron, by Kees Van Heiden:
https://www.youtube.com/watch?v=pSjpzta0FuY

Another by Kees, only with a wooden plane:
https://www.youtube.com/watch?v=P3Nq1sbOhMM

A nice short article, with video, by Chris Schwarz:
http://www.popularwoodworking.com/woodworking-blogs/chris-schwarz-blog/fine-tune-a-handplanes-back-iron

A longer video on setting the cap iron, by Richard McGuire:
https://www.youtube.com/watch?v=xmDVa5cxq8w

A thoroughly-researched study on cap irons:
http://planetuning.infillplane.com/html/cap_iron_study_by_kees_van_der.html

My own three-part history of the double iron starts here:
http://blackdogswoodshop.blogspot.com/2016/03/the-double-iron-part-1.html