This question comes from Adam B. He asks:
Marc, I am watching your Entertainment Center Video (Pt 1) and noticed something odd with your large chisel. How did you flatten the back of it? It looks like there are three channels cut into it.
The chisels I use on the show (most times) are Fujihiro Japanese chisels. In general, Japanese chisels are made with harder steel than their Western cousins, which means it can take a lot longer to flatten their backs. And a flat back is an absolutely critical component to any chisel you actually intend to use! So to speed up the flattening process, a good amount of steel is removed from the back of the chisel. And as you can see in the picture, wider chisels can have multiple hollows. So now the actual amount of steel that needs to be removed in the flattening process is significantly reduced. Which means you are going to spend less time at the sharpening stone, and more time at the workbench.
This is the same concept behind creating a hollow bevel. Many folks prefer hollow bevels because they can be easier to sharpen, not just because of speed, but because its easier to balance with two points of contact. FYI, some may disagree with me on this but this is just my opinion from my experience. So the hollows are a little unusual-looking, but they do serve a purpose.
I borrowed the image to the right from a great article on FineWoodworking.com called “Speedy Freehand Sharpening” by Hendrik Varjhu.