January 2018


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What Steel Gets Sharpest

by John Lucas

This is a debate that goes on forever. Ever since I started wood working, people have been arguing about which steel gets the sharpest. Thirty-five years ago it was pretty well accepted that high carbon steel would get sharper and carbide simply would not get to a keen edge. Well, things have changed. I recently heard someone echo the statement that high carbon steel would get sharper and particle metal steel would not get sharp. Well, I was pretty sure that might not be true anymore. A few years ago I did a test on skews and how they are ground. I didn’t plan it that way, but it turns out I had skews made from all sorts of steels. They all seemed to take an edge well enough to shave hair. This led me to doubt the earlier statement. So I set out to see if I could prove it one way or the other.

I acquired three tools: a high carbon steel bar, a Sorby High Speed Steel tool and a Thompson V11 particle metal tool. All were 3/8” thick and 1” wide. I ground the front edge square with a double bevel like a skew. I ground all of these to the same angle which turned out to be 27 degrees. I had set my Veritas sharpening jig to the 25-degree angle and after creating a micro bevel on each tool it came out to 27. Each tool was sharpened using the scary sharp technique of sandpaper on plate glass. I sharpened them to 2000 grit. I sharpened until I raised a burr and then flipped the tool and again sharpened until I raised a burr on the other side. Then I went to the next grit. I had done some research and 8000 grit waterstones that are a Japanese standard were rated somewhere around 1200 to 1500 sandpaper grit, depending on who you believe. So that is why I went a step further.   I then stropped the tools to get a keener edge.

I did find out that the particle metal took a few more strokes to get the same edge. I also learned that the gold stropping bars used by carvers seemed to work faster on the particle metal. For the test I used the green bar (Chrome Oxide Compound) on all tools so they were all sharpened the same.

I took all the tools and shaved my arm bald and they all sliced through paper easier than almost any tool I have ever sharpened. I could not tell the difference. These tools were easily as sharp as my carving tools or better. So the initial answer to my question was simple.  All three metals sharpened the same. But I wasn’t satisfied with that. I tried looking at the edge under a microscope, but I simply didn’t have the proper tool for that.   I worked for Tennessee Tech University before retirement and called a friend who works in the Engineering department. I asked if he could help with photographing the edges at high magnification. They were nice enough to help me with this. When I first talked to my friend, I had suggested 200 or 400 times magnification because that is what Alan Lacer used in his wonderful article on how honing improves the edge and the cut quality. We found out pretty quickly that my tools were far too sharp for this. Wayne suggested the Scanning Electron microscope which required cutting the tips off the tools to be able to fit into the machine. I took them home and gritted my teeth as I cut 2” off the tools. I hated to do that, but it was for a good cause. 

When I got back, we started at 200X and the edge was perfectly straight. We kept increasing the magnification, looking for that sawtooth edge that would hopefully tell me something. We had to go all the way to 2500X before we could see a deformed edge. At 5000X we could see it clearly. At this magnification it appeared that the HSS edge was little finer. Of course, we are talking about an extremely small difference.  Here are the photos so you can see.

High Carbon Steel - 200X

High Carbon Steel - 5000X

High Speed Steel - 200X

High Speed Steel - 5000X

V11 Particle Metal - 200X

V11 Particle Metal - 5000X

I was explaining this to a friend who happened to own a BESS blade sharpening tester. So I borrowed this and rigged up a jig to hold my tools. With this machine, you cut through a known test medium and it measures how much force is needed to cut this medium, which is a good comparison of edge sharpness. I tested each tool. The high carbon steel and the particle metal steel tested virtually identical. The HSS tested less sharp, which was surprising after seeing the scanned images. I did this test three times and came to the same results. Again, I have to stress the differences are extremely small: they averaged just seven grams different. I tested lots of other things to see how the tools compared and you can see that in the chart I included.

You often hear the term "sharp as a razor".  Well, I found out pretty quickly that it depends on the razor. These tools tested sharper than a standard utility razor blade, but not quite as sharp as a high quality single edge razor blade. They did test sharper than any of my kitchen knives that I keep “razor” sharp, meaning they shave hair. I tested several of my carving tools and they were slightly duller than my test steels. I have two chip-carving knives that both tested sharper, but then they are also ground at a more acute angle and have very thin blades. The angle of the sharpened edge does have a bearing on how sharp they test. Single-edge razor blades were about 20 degrees and double-edge (which tested the sharpest of all the edges I tested) seemed to be more acute than 20, but was very hard to read using the angle scale I had. Doing these tests also opened my eyes up to the term "razor sharp". There are obviously various degrees of razor sharp. By stropping my single edge razor, I was able to get it sharper than my chip carving tool, but not nearly as sharp as a double-edge razor. All this testing further proved in my eye that all of the steels would sharpen to the same degree. It also demonstrated that they would sharpen further than most of us will ever need, especially for turning. 

Well, this was fun, but then I realized that I had not tested any carbide tools. I happen to have some brand new Hunter cutters, so I called my friend back up. I can’t say enough how helpful he is. I made a special holder to hold the tool at the correct angle and took them back up to TTU. I didn’t have any idea what to expect. I knew the Hunter cutters came sharp because I had cut myself on them. I knew they had much smaller carbide particle than earlier carbides and thought they might have a better edge. As you can see in the photo, they have a very different look than the straight edges, but then this is a curved cutter.

Hunter Cutter - 200X Magnification

Hunter Cutter - 5000X Magnification

I really wasn’t expecting that undulating look. Again, we had to go to very high magnification to even see a difference. It was obvious this wasn’t as sharp as the other tools, but was still very sharp. When I got home I again made a new jig to be able to use the BESS sharpness tester. The tool tested just barely less sharp than my utility razor blade and that really surprised me. It tested sharper than most of my kitchen knives. I tested two other smaller cutters right out of the box and got similar results. These tools are sharp. As a comparison, I took my Thompson Spindle gouge, sharpened it on my 180 grit CBN wheel, and then honed the edge using a 600 grit diamond hone. This tool tested less sharp than the kitchen knives but was still very sharp. Not quite as good as the Hunter cutters, but in tests on real wood it leaves a super clean cut. Now I do need to take into consideration this tool has a 40-degree included angle, so it will never cut as well as a 27-degree angle. The Hunter cutters have somewhere around a 30-degree edge--which is why they cut so well. My kitchen knives have about a 25-degree angle. 

Now some will argue about my tests, but I have sharpened enough different steels over the years to feel that what I found is accurate. Your sharpening skill will have much more to do with how sharp a tool gets than the material. So don’t worry about the steel, it will do the job. Practice your sharpening techniques. There are differences in steel quality, however. I bought four tools from Harbour Freight. Two of them hold an edge just as well as my Sorby tools. Two of them won’t hold an edge at all. If you buy quality steel from the beginning you won’t have that problem.

Now edge holding is a whole different thing, and I simply don’t have the tools or skills to do a really good test of that. I was going to try a simple test, but when I had to cut the tools down to 2” that ruled that out. I will say from my experience the carbon steel is the least durable, the particle metal is a little better than HSS, and the carbide is the longest. But as you know, that’s just from personal use and not definitive from a scientific standpoint. If you sharpen very frequently, which you should, then the difference in edge holding is really marginal.

Click here to read about the author, John Lucas.