I have been following with considerable interest the recent, lengthy discussion at WoodCentral.com about that plane accessory known variously as a chip breaker, cap iron, back iron, second iron, etc. It seems the name “Chip Breaker” is the winner in the terminology competition. Bill Tindall started the discussion (IIRC) with the rediscovery of a video made by Professor Yasunori Kawai and Honorary Professor Chutaro Kato, Faculty of Education, Art and Science, Yamagata University, in 1989 that shows an up-close-and-personal view of the cutting action of a plane blade and reveals, in a video-is-worth-a-million-words kind of way the benefits of using, and how to properly set, the chip breaker.
A zillion back and forth posts ensued asking, positing, clarifying and arguing (all very politely). Along the way Wilbur Pan captioned the video, Steve Elliott added his research results, even Chris Schwarz added to the knowledge base, TWICE! And finally, David Weaver wrote up the whole magillah in a straightforward, readable tome with Ellis Walentine’s most excellent diagram (above.)
Bottom line: chip breakers help prevent tearout when set Very Close to the cutting edge. And a microbevel on the edge of the breaker — steeper than you ever imagined — can seem to perform miracles.
Good work, all! My compliments and thanks to everyone who contributed.