Why a Chipbreaker is called a Chipbreaker

May 1, 2012 Comments Off on Why a Chipbreaker is called a Chipbreaker

There have been some terrific discussions of late on WoodCentral in regards to chipbreakers, sometimes called cap irons on planes. As hand plane sementics have evolved over the years, the term cap iron has been used more and more. Many describe its function as merely to hold the plane iron in place, acting to stiffen the cutting edge. The discussions on WoodCentral have, at least for me, refocused some of the attention on the “chipbreaker” function of the double iron. Experiments by Chutaro Kato in Japan, using a large mechanized supersurfacer planer, have clearly shown the importance of the chipbreaker in reducing tearout. The video shown at this website is fascinating. (Update: Wilbur Pan has uploaded an enhanced version of the video to his Vimeo account here). If you then scroll down towards the bottom of the page and start reading after the title “Effect of Knife Chipbreakers on Surface Finish”, Kato summarizes the experiments in written form. In short, putting a steep 80° microbevel on a chipbreaker that is placed very near the cutting edge yielded the best results (and this was planing against the grain). The video documents this in stunning detail.  This is a not a new idea; many woodworkers have been advocating the use of a chipbreaker to reduce tearout for years. I’ll experiment with a chipbreaker over the next few weeks and see what happens.

Woodworking forums on the web can be distracting; there is a lot of noise to filter through. But you do get some eye-opening discussions now and again. Below are a few links to some of the threads discussing chipbreakers and supersurfacers. There are more, so if you’re interested take a little time and peruse some of the forum threads over the last few weeks.  (And these links won’t last too long, as more threads get added, the site addresses will change).

http://www.woodcentral.com/woodworking/forum/handtools.pl/page/1/md/read/id/447521/sbj/awesome-planing-video/

http://www.woodcentral.com/woodworking/forum/handtools.pl/page/2/md/read/id/447363/sbj/cap-iron-question-need-data/

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