Steep secondary bevel shaves wood better?

M

matthew rapaport

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Jun 23, 1999
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OK, I wonder if anyone, esp. Cliff, has noticed anything like the following effect....

I bougtht a hunting knife from Eric Chang. This knife is relatively thick at the spine (5/32"), and very very thin at the end of its beautiful flat-to-the-spine grind at .014"! Eric sent it to me with a very steep (maybe 22 deg/side) secondary bevel.

To build a fire, I often shave thin slices of wood from some pine that I have which is loaded with pitch. NIB, Eric's knife did that shaving far more easily, and with far more control than any other knife I own except a Dozier Master Hunter that happens also to still have its factory edge, and is also a somewhat heavy knife. I should note that at the same time this same Dozier slides through 3/8" hemp rope almost effortlessly!

As well as Eric's knife shaved wood however, it was one of the worst cutters of hemp rope I have dispite its NIB ability to shave hair. It had a very smooth edge. So I thinned the secondary bevel of this knife to perhaps 17 deg/side and finished it a little more coarse with a 325 grit diamond stone. Now Eric's knife slices rope very easily (though not quite as easily as the Dozier), but <i>its performance as a wood shaver has degraded to just above the level of most of my other knives</i>. I'm really wondering what it is about the thinner/coarser secondary bevel that causes this? That's all I changed... Honest!
:eek:
 
Heck, I'll jump in here. I did a bunch of whittling tests just last night, on a number of my knives. My Dozier K-4, large Sebenza and PCKS Buck 110 were three of them. The Buck 110, which I'd given a much more polished edge bevel, whittled quite a bit better than the coarser honed Dozier and Sebenza. I guess that push cuts just demand a polished edge. That's not so good for other utility chores, but awesome for whittling.
 
When you are shaving wood, you are not simply cutting into it, as you are when you are slicing through the hemp rope. On the wood, you cut into it and then turn the blade up and run it along the wood. It is the turning up that is causing the problem. The more obtuse the bevel that is facing into the wood, the easier this gets because of a leverage advantage. Thus when you made it more acute, it got harder to turn because it "wanted" to keep going deeper into the wood. What you can do to avoid this but raise the rope cutting ability is make the bevel on one side 22, but on the other side 12. Now the overall profile is the same as if both were 17 (in regards to included angle), so the rope sees a similar force as you wedge there from both sides. However the wood whittling doesn't see as much of a difference as if both were reduced down to 17 [I have not tested that but it seems logical - I'll try it in a day or two]. Chisels are often back beveled slightly, making them in effect v-ground to improve this aspect of cutting ability. It is sort of counter intuitive as you are making the included profile more obtuse, yet the cutting ablility is increasing as you are gaining control. Of course, the coarse edge didn't help the push cutting ability at all, it acts to directly decrease it. But even at the same polish, the wood shaving ability would have taken a drastic decrease.

-Cliff
 
Cliff,

This is a new idea to me and I am quite curious about the results you will get. Does this technique require that you make your knive a dedicated right or left-handed one? That is, does the more obtuse angled edge bevel need to be held against the wood being whittled?
 
On the wood, you cut into it and then turn the blade up and run it along the wood. It is the turning up that is causing the problem. The more obtuse the bevel that is facing into the wood, the easier this gets because of a leverage advantage. Thus when you made it more acute, it got harder to turn because it "wanted" to keep going deeper into the wood.
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This is a very interesting idea. All of my other knives do pretty well shaving very thin slices off the pitch-laden wood. You are correct in that if I try to make them dig a little deeper to make slightly thicker slices, I have a hard time controlling their depth, and not just controlling them, but even pushing them through at all. The more obtuse edge however controlled easily, and also pushed through the medium pretty easily at varying depths (none deeper than about 1/16") that was what was so noticably different. Of course you are also right about the negative effect of the coarser edge.
 
on a chisel grind you want the non ground side to the inside of the body were you have more strength and control so for a right hander i would put the 12dg bevel on the side you look at with the knife in your right hand and the 22dg bevel on the the obverse side. this wil lessen the tendence for the knife to roll over. i am sure you have heard of the TACTICAL chisel grinds to roll inwards while slice cutting? this is because they are ground for a lefty.
 
for the whittiling put the 22dg on the in side and the 12dg on the obverse. thats for right handers.:footinmou
 
Geode :

does the more obtuse angled edge bevel need to be held against the wood being whittled?
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If the more obtuse bevel is against the wood you have better control (can turn it easier). I finally tested this out last night. It is is interesting, by making the bevel uneven, you have a sort of dual functionality. If you put the acute bevel on the inside you can rough off stock fast, however if you put the obtuse bevel on the inside you can whittle much easier. You can see the difference on food prep as well, peeling potatoes and turnips etc. .

-Cliff
 
Laurence and Cliff,

Your insights in having dual edge bevels in this thread have been some of the most valuable ones to me since following the BF. Thanks again - now I am going to make myself semi-ambidexterous so that I can use either bevel on a dual bevel knife.

The Edgepro will be getting a workout the next few weeks.
 
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