Sharpening Kanna : an Evolving Method 7

Back with more sharpening this week.

I’ve been experimenting with different techniques to see if there are any ways to improve upon my current setup. So below are a few experiments using a Japanese natural stone, 3M 0.5 Micron lapping film, and finally my usual method with varying levels of pressure used on the micro-bevel. I used the same white steel kanna for each round of sharpening.

All the images are the same resolution taken on my camera/microscope setup with approximately 400 x magnification. On two of the images I inserted a 10 micron scale line for reference.

The first experiment went as follows:

• 3000 grit Naniwa Chosera – Ura Touch-up
• 6000 grit Diamond – Ura Touch-up
• 1000 grit Naniwa Chosera
• 3000 grit Naniwa Chosera
• Japanese Natural Stone – Full Bevel
• Japanese Natural Stone – Micro-bevel/Ura

Compared to my previous attempts using a natural stone for micro-bevel sharpening, this time I went really light on pressure. You can see how the scratches change direction three times, showing the direction of the full bevel scratches and two attempts at the micro bevel. The results were pretty similar to what I’ve found in the past, with the edge looking and feeling pretty jagged. My sense in the past was that the grit in my natural stone are on the coarser side, and compared to working the full bevel which may break the grit down a bit more, allowing sharpening to happen more with the slurry of the stone, sharpening a micro-bevel has a tendency to cut right through any slurry and the edge simply scrapes along on the surface. So this time around I had thought that going super light might allow the micro-bevel to “float” on the surface of the stone and interact with the slurry a bit more, but that doesn’t seem to really be the case, or at least not in any meaningful way.

Here’s how things went for the next experiment:

• 1000 grit Naniwa Chosera
• 3000 grit Naniwa Chosera
• 8000 grit Kitayama Stone – Micro-bevel
• 12000 grit Naniwa Kagiyaki – Micro-bevel
• 12000 grit Naniwa Kagiyaki – Ura
• 3M 0.5 Micron Lapping Sheet – Micro-bevel Pull Strokes
• 12000 grit Naniwa Kagiyaki – Ura

This really didn’t turn out well. I’m not used to lapping sheets, and perhaps my technique was poor, but the resulting edge really chipped out. I used a flat whetstone as a base for the lapping sheet as well as a touch of water for lubricant, but after a few passes the sheet felt like it quickly plugged up, creating lots of finely raised areas that had the effect of micro-chipping the whole edge.

Finally I resharpened this blade one last time using my usual method, and this time simply tested out the level of pressure used when doing the micro-bevel. The general process went like this:

• 1000 grit Naniwa Chosera
• 3000 grit Naniwa Chosera
• 8000 grit Kitayama Stone – Micro-bevel/Ura
• 12000 grit Naniwa Kagiyaki – Micro-bevel/Ura

With the blade below I used very little pressure when doing the micro-bevel, attempting to really just let the weight of the blade do the work.

The result is okay, but still a bit jagged.

Next I applied a touch more pressure, and the edge definitely cleaned up. You can see one little micro-chip as well as a little bit of a burr that remains attached.

Finally I sharpened the micro-bevel using pretty firm pressure. I certainly wasn’t bearing down on the blade with my full body weight, but definitely used more force than I thought would be necessary, especially for a micro-bevel which is such a small area.

This time the edge turned out to be the cleanest, with the least amount of micro-chipping and wispy bits of burr hanging on, and it also felt the sharpest when running the blade over the hair on my arm.

Using firm pressure on the micro-bevel is something that a friend and I have found to be effective for some time now. A while back working in Okayama, I was using a blade that consistently was ending up with a jagged edge. No matter how much I tried I couldn’t get rid of what looked like micro-chips and burr along the edge. My instinct was to be more gentle with the blade and to go lighter when doing the micro-bevel, but that clearly wasn’t solving the problem. My buddy who was sharpening next to me was taking much more of a “brute force” approach to sharpening his blade and comparing his to mine under the microscope, the results were clear; his edge looked better and it planed better. So a couple passes more on the micro-bevel using some firm pressure, and I had completely eliminated the micro-chips and burr.

That’s the story this week. I should be getting my hands on some decent hinoki for planing practice soon, so I’ll try to supplement these sharpening posts with what this is really all about, planing wood.