Help with bevel length change at tip compared to the rest of the edge?

G

Geneh2001

Joined
Sep 14, 2010
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Let's see if I can articulate my question: I see more bevel closer to the tip of my blades than on the flats. Most of my blades are flat or full flat grind. Assume the bevel angle is constant, but I think it is because the blade is thicker at the back than the edge. When I see pictures of knifes most of them show a bevel that is the same from tip to tail.

Is this a problem for a general purpose outdoors bushcrafting or camping knife? Weaker tip prone to damage? I don't slice with the tip, I slice with the flat and curve, and on a bigger knife might use it to split smaller wood if lacking a wedge or hatchet. (And as much as I like to get out, I don't very much, so do not have enough hands-on experience...)

Or is this an aesthetic issue that indicates a noob or careless technique? Currently I'm using EdgePro. I had a Lansky-type which did change the angle towards the tip, but with the EP I keep the stone in the same area and move the knife according to instruction videos.

The top blade is a RAT-7, hopefully you can see the new bevel edge that would be cut, then the blue marker showing the original bevel. The bottom blade shows the issue I'm talking about very well. The blade is the same thickness across the back. The flat edge is very thin and shows almost no bevel length, but the tip on has a very long bevel length.



th_Rat7andGRBevelAngle1_zps4a23ae6f.jpg
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th_Rat7andGRBevelAngle2_zps6275c9e3.jpg
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This is due to keeping a constant angle when sharpening. I don't worry about it at all. Basically, if the distal taper doesn't match the decreasing width, this will happen. Very few knives match those two parameters up.
 
I just replied to a similar question in another thread, regarding a difference in bevel width near the tip, with some variation in width of the bevels between each side. The issues appear to be similar in some respects, in that it has to do with how the blades are ground by the maker/manufacturer:

Obsessed with Edges said:
Assuming that's the factory bevel, the asymmetry is very common (on almost all knives, not just that one). The primary grind on most blades will be somewhat asymmetrical, though most of the time it's not a problem. The asymmetrical grind itself leaves the steel a little thicker on one side (relative to the centerline of the blade, drawn from the center of the spine down to the apex of the cutting edge). When the steel is thicker on one side like this, a wider bevel will always result on the thicker side, when sharpening each side to the same angle.

A similar effect (wider bevel) can be produced on a more symmetrically-ground blade, if the sharpening angle on one side is more acute (lower angle) than on the other side. The more acute side will have a wider bevel.

If you're sure the sharpening angle on each side is the same (or fairly close), and you can verify you're contacting the edge when sharpening on both sides, I wouldn't worry too much (or at all) about the bevel being a litte wider on one side. Under that circumstance, it's mainly a cosmetic issue and won't affect functionality at all.

If, on the other hand, you're noticing that the edge isn't making contact with the hone on one side (but the shoulder of the bevel is), it may be that the edge angles are different on each side, which will only create frustrating sharpening difficulties until it's evened out by re-bevelling, a.k.a. re-profiling the edge to better symmetry.
Click to expand...

Additionally, even with symmetrically-ground blades, as the cutting edge sweeps toward the tip, up into thicker steel near the spine, the bevel width will always get wider, if the same sharpening angle is maintained (as would be the case using a guided sharpener, like the EP/WickedEdge/Lansky/Gatco/Aligner/etc).

On knives that appear to have a uniform bevel width all the way to the tip, this is because the sharpening angle had to have been increased (made more obtuse), as the cutting edge sweeps up toward the thicker steel near the intersection of the spine & tip. This is more common on factory edge bevels, which look good, but the angle near the tip is always a lot more obtuse than it is further back into the body of the blade, where the steel at the cutting edge is further from the spine, and therefore thinner (assuming a tapered grind from spine to edge).


David
 
Good to know. Thought it was just me. I didn't see that other thread - will have to search a bit better. Thank you!
 
Depending on the type of grind it can be hard to maintain the same edge thickness all the way around the curve of the belly of the knife blade. There are various hollow ground blades where the hollow grind follows the curve of the blade, these can maintain the same edge thickness for the entire edge but the point of one of these doesn't seem too strong to me.

A FFG blade will naturally have a thicker edge at the point, the geometry forces it to. A Spyderco FFG is tilted both ways which is visible if you look at the spine of the blade, so the edge is the narrowest about halfway around the belly, and still thicker at the point and near the choil. I wonder if they fudge a bit on the FFG so the edge is more uniform. I have a Para 2 but I haven't checked this theory.

But back to the subject- if the grind makes the edge thickness greater at the point, and you sharpen at a consistent angle all the way around, then the edge grind will be wider at the point. If the increased edge of the grind bothers you then the solution is to use a different angle near the point. I've studied various grinds to see how they resolve these inconsistencies in the geometry and I find a few knives that have interesting solutions. The first is the Spyderco Vallotton. In this one you can see that it has a hollow grind that makes the edge thin along the bottom of the blade, but as it curves up towards the point they changed to a convex grind and the depth of the grind increased. Another knife that I find with an interesting grind is the Hinderer. The blade has a grind that looks a lot like a tanto grind meaning flat grinds in 2 different directions, but the blade has a more conventional curve. The dual flat grinds allow a blade with a strong point but flat grinds and a curved belly.

I'm not sure if a thicker edge and wider grind is weaker, maybe it is stronger because the material right behind the edge is thicker. It can be made even stronger with a different grind angle. For a utility or bushcraft knife I'm not sure if this is required. If you anticipate needing to stab through tough materials then a different grind angle probably doesn't matter.
 
bdmicarta said:
Depending on the type of grind it can be hard to maintain the same edge thickness all the way around the curve of the belly of the knife blade. ... A FFG blade will naturally have a thicker edge at the point, the geometry forces it to...if the grind makes the edge thickness greater at the point, and you sharpen at a consistent angle all the way around, then the edge grind will be wider at the point. If the increased edge of the grind bothers you ...I'm not sure if a thicker edge and wider grind is weaker, maybe it is stronger because the material right behind the edge is thicker. It can be made even stronger with a different grind angle. For a utility or bushcraft knife I'm not sure if this is required. If you anticipate needing to stab through tough materials then a different grind angle probably doesn't matter.
Click to expand...

Nope, doesn't bother me as long as it is expected and correct - not a error on my part. I would really hate to think I'm sharpening correctly and then have someone come up and say, "you're doing it wrong..." I don't think I'll be stabbing through something tough but the thought of a weak tip, again because of incorrect bevel angle, bothers me. Since everyone so far agrees, "not a problem," I'm happy with that.

Thank you!!
 
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