Hand Tools

Subject:
Update 3 - the well-tempered blade

Winston
As I mentioned in another post, I tempered the blade in my oven at 340 F for about an hour. I put it in a cast iron pan and put a baking sheet on the rack above (to block any radiant heat), and used an IR thermometer to take temperature readings of the pan. I had set the oven to 360 degrees, but the temperature of the pan stabilized at 340, which I thought was a good temperature. I put the blade on the pan and let it sit in there for an hour or so. I took occasional temperature readings, which were all within a 5 degrees of 340. When I took it out of the oven, it had a faint golden hue.

So far, it seems like this has worked out as well as I could possibly have hoped.

I sharpened the blade on the Norton 1000, Shapton 5000, Shapton 12000 sequence, and this time it went without a hitch. It was just like sharpening any other blade. There were no chips from the 1000 stone to work out at the finer grits, so I only had to spend a around a minute on each of the finer stones.

People here seemed to like the previous pictures, so here are some of the sharpening sequence. I took a photo after each grit.

The post-12000 photo reveals that I could have spent more time on it, and there may have been some larger grit contamination. But I also think it looks more scratched than it really was due to the angle of the light. In any case, the resulting wood surface was once again glassy smooth, with no tracks.

This made me think, was all the stuff that happened before just in my head? Fortunately, I have the pictures to confirm that yes, it really was that bad before. If you look at the photos from my Update 2, you can see how much worse it was, and how long it took to improve the edge.

I decided to really press my luck and try using the Trend diamond 1000 plate before the 5000 and 12000 stones. Here's the result:

There were some edge defects that are clearly visible the post-5000 and -12000 photos, but only in one small region of the blade. (There are also some paper towel fibers in the post-12000 picture, which should be ignored.) The edge defects look small, but based on my previous experience, I think they would have left noticeable tracks in wood, especially if they crumbled and resulted in even larger defects.

I'm actually kind of glad that there was still a little chipping in this sharpening sequence, because it confirms that the phenomenon was and is real. Even though I have the chipped-blade pictures from before re-tempering the blade, it's still a little hard for me to believe that it really happened and was that bad. The fact that it still chips a little bit with the diamonds tells me that yes, the chipping is/was real, and also that I didn't overdo the tempering of the blade.

David said that he thought there was a 25% chance that the issue would be solvable. I think I may have lucked out. I haven't used the blade enough to get a good sense of how the edge will hold up, but in my limited testing so far, it seems good -- and, as I understand it, the mild tempering that I did should still result in hard steel (around 63 Rc according to David).

Thanks all for your ideas and feedback about how to deal with this blade!

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