A subject, rife for endless discussions. Does the chipbreaker really break chips or is it just there to stabilise the blade and as a convenient point to attach the depth adjuster? The last few years this was not quite clear among all woodworkers. I was also sceptic about the usefullness of the thing. Then the legendary Kato video turned up again, after seemingly being lost for some decades. It really opened my eyes.
Prof Kawai and prof Kato from Japan have done extensive research to the behaviour of planing blades in wood. As a tutorial for their students they made a video showing how the chipbreaker works when planing against the wood in 1989. A link to this video and some other information is to be found on this page:
While I was allready playing with the chipbreaker, the results were not very convincing. I meassured the distance between the cutting edge and the chipbreaker at 0.4mm and thought that was very close. The video motivated me to go even somewhat further. At 0.2mm I finally got the results I was looking for. Being able to use a dirt cheap plane on all kinds of wood with grain reversals, knots, curly stuff, ribbon striped, crossgrained, and all that without tear out!
Tear out is the bane of the handplane. You can make a wonderfull surfaces with a plane, much nicer then when using sandpaper. But as soon as the grain of the wood doesn't cooperate, you get tear out, meaning big chunks being ripped from the surface and thus ruining that nice smooth surface. There are quite a few very expensive planes on the market specialy designed to mitigate tear out. So it is pretty spectacular when you can do the same with a 20 euro Stanley #4 or even a 5 euro wooden coffin smoother.
Of course this is all nothing new. The knowledge has been available since the invention of the chipbreaker in the 18th century. But the video from Kato is so clear and so obvious, it's difficult not to be impressed.
In order to help other woodworkers who are still not getting the maximum performance from their bevel down, double iron planes, I made two videos. The first is strictly an instructional video. The second one, just shows some more detail and (I think) a quite spectaculair case of tear out being repaired with the chipbreaker at the proper depth.