Hand Tools Archive

Kanna blade sharpening issues *PIC*

I recently acquired a Japanese plane, and I've been having some trouble getting the blade really sharp. This is my first kanna, and it's not a fancy one -- it's an Senkichi with a laminated blade.

The first thing I did with the blade was to flatten the back. This took a long time because the corners had a bit of lift to them. After tuning up the dai and making my first shavings, I noticed I wasn't getting anything near a smooth surface. When I took a look at the blade's edge with a 30x loupe, I could see that it was chipped and ragged.

The blade came with a 25-degree bevel angle, so I worked on increasing it to 30 degrees. (The bedding angle of the dai is 40 degrees.) After going through many rounds sharpening and making shavings, I found that even with the 30 degree bevel, I had a really hard time avoiding a chipped edge and plane tracks. Maybe one out of four sharpenings I was able to get a pristine, track-free surface, but when I did, it was beautiful. It's been frustrating because I've been able to get great results, just not consistently. (In my testing, in the best case, I've been able to get about full-width shavings from a pine 2x4 that are approximately .0008 inches thick, and not-quite-full-width shavings that are .0005 inch. My micrometer only has markings for .001 inch, so those values are estimates. Not that I'm trying to get ultra-fine shavings normally, but this is a way for me to test whether I'm doing a good job sharpening the blade.)

The sequence of stones I've been using for sharpening is: 1000-grit Trend diamond plate, 5000-grit Shapton pro, then 12000-grit Shapton pro. I usually only work the bevel side until the finest stone; my last step is to work the back, and I usually don't go back and forth between the sides. I've been using an Eclipse-style honing guide (don't judge me!) because I've been working on increasing the bevel angle from 25 to 30 degrees, and I don't yet have a large enough 30-degree bevel to do it freehand.

In my most recent time sharpening, I realized that I've been having a hard time raising a burr on this blade with the 1000-grit diamond plate. When I took a look at the back of the blade through the loupe after the 1000-grit plate, I saw that the edge was chipped and there was no burr (or at least not one that I could see or feel).

My theory is that the steel is much harder than the blades I'm accustomed to, and the fixed diamonds end up fracturing the steel. Is this something that anyone else has experienced with Japanese blades?

I then switched to a 1000-grit Norton waterstone, and with that stone I was able to raise a burr. My theory is that the loose grit rolling around can't fracture the steel the same way that the fixed diamonds do. Then I moved on to 5000-grit Shapton. After working the bevel side for a while, I could see and feel that the burr on the back was much smaller. However, there was also a tiny dip on the back just before the burr. (This is sort of like there was a back bevel.)

After working the bevel side on to the 12000-grit Shapton, the burr was pretty much gone, but the dip/"back bevel" was still there. Now, I've always worked the back of this blade flat -- I've never tried to add any sort of back bevel on it, and I flatten my stones often. With this mini back bevel, when I work the back of the blade on the flat stone, it doesn't quite reach the cutting edge, which prevents it from getting really, really sharp.

At first I thought that maybe the blade just had a slight convexity at the edge, and that honing the bevel a bit more would make the "back bevel" go away. But no matter how much I work the bevel side, the "back bevel" is always there.

Does anyone know if the "back bevel" has something to do with the steel in this blade? Or is it something else? I'm not sure, but I think I may have seen this on other blades, but it seems more pronounced with this blade. With the Eclipse guide, the blade only moves back and forth. Is it possible that on the forward stroke, the slurry in front of the edge is abrading the steel, causing the "back bevel"?

If anyone can help enlighten me about why these things are happening and how to deal with them, I'd appreciate it.

Here's a picture of the blade after the 1000-grit Norton and 5000-grit Shapton. There's still a small burr, but the angle of the reflection indicates that there's also a back bevel.

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