Why cant i get thin blades as sharp as thick blades

J

jamiesaun

Joined
Jan 1, 2016
Messages
44
So, when I sharpen a blade with some girth behind the cutting edge, they turn out scary sharp. But when I try to sharpen a realy thin blade, they turn out just so so. I still get them pretty sharp, they'll slice paper and shave okay, but they don't clean shave like a thicker blade will when I'm done with it.

I suspect this is for 2 reasons. First, the bevel is so tiny that it's harder to keep it consistent. And second, it's almost like the edge is rolling, no matter what I do to try to avoid it. Like the edge is so thin that it just rolls on the strop. I can't really feel any burrs though, so I am at a loss and ready to give up on really thin blades.

I use the same process for both types of blades, but they turn out quite different.

Anybody know why I have a problem with really thin blades, but can sharpen a thicker blade with the best of 'em?

Thanks in advance
 
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Increase the angle on the thin items until you find a sweet spot that doesn't roll over and keeps its edge.
 
Thanks for the tip. I had considered that, But won't that make the bevel really small? Does it not matter if the bevel is super tiny? Like a 1/32 or whatever?
 
That OK. Thin knives are going to have small bevels. The point is sharpening the tool to task. So it does the job it was meant to do.
 
When you say thin, do you mean spine thickness? Or distance from edge to spine? I think you mean spine (body) thickness, but I wanted to clarify.

Brian.
 
If you're rolling the edge off a strop, I'd guess you have a wire edge.

Thin edges and narrow bevels stone to the apex much faster than thick edges with wide bevels. So if you're sharpening both types of edge geometries the same, you're over-sharpening the thin edges which is creating that big burr.

I'd try a lighter touch, watching carefully for a burr.
 
Is this a problem with one particular knife or all knives that are thin behind the edge? Maybe you are using to much pressure on the stone/strop and the edge is deforming slightly?
 
You are correct. But more like blade thickness. Like a hollow ground knife. The blade is super thin behind the cutting edge
 
This is my guess too. It's with all knifes that are thin behind the edge. I can get them pretty sharp, but not as sharp as thicker blades, and I'm not really sure why yet.
 
I sorta get where the OP is going with this, I think. Thin spines, and super thin edges (.005" and under), just don't have that same feel as a thicker edge does when you take that apex to your fingertips. It may be just simply there is more mass in the thicker edge, so that translates better to your sense of feeling in your fingertips. But take that thin knife and cut thru cardboard, and there is no question, it's wicked sharp and the thin geometry allows for an efficient cut. Sort of like a blade on a safety razor vs the edge on a chef's knife that has a .010" edge before sharpening. Yeah, no question the razor is sharp, but that relatively "large" edge bevel on the chef's knife just feels sharper on the fingers (when sharpened well)....to me anyway.
 
This is kind-of what I was wondering. Am I over sharpening, as in getting the edge so thin that it just rolls over to one side, then rolls over to the other side. Like tin foil or something.

I'll try what pjwoolw suggested which is increase the bevel angle. Hopefully this works.
 
jamiesaun said:
This is my guess too. It's with all knifes that are thin behind the edge. I can get them pretty sharp, but not as sharp as thicker blades, and I'm not really sure why yet.
Click to expand...

For very thin-edged blades, the inherently narrower bevels (on edges that have secondary bevels) are much more difficult to stablilize and 'feel' when honing or stropping; more so, if your edge angles are relatively high (wide) at or beyond 40° inclusive. Wider (more obtuse) edge angles will make the bevels even narrower, for a given blade/edge thickness. That's likely what you're having trouble with, as previously mentioned. There may also be issues with too much pressure used on the narrower bevels, which can also aggravate edge-rounding on softer strops of leather or thicker fabrics.

An alternative is to profile your edges at a lower angle to a 'zero edge' or 'zero grind', on which the primary grind of the blade, or a significant portion of it, is essentially honed directly to a sharp apex, with no distinct, narrow secondary bevel behind the edge. Done this way, it's much easier to feel larger expanse of the primary grind on a hone or strop (because the blade is held to a much lower angle), and thin edges can be honed to extreme sharpness pretty easily. Usually, in the absence of distinct secondary bevels, some convexity will result near/close to the edge, unless the whole blade is laid dead-flat to the hone or strop. That being said, the lower honing angle makes stabilizing the blade much easier. The pic below is an illustration of a lowered approach on one of my knives (Buck 301 folder), showing the resulting convexed & polished portions which replaced the factory edge bevels, which were obviously narrower. In the pics, the shiny portions near the edge may look like wider bevels, though there's no longer a distinct 'shoulder' on them.


David
 
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Obsessed with Edges said:
For very thin-edged blades, the inherently narrower bevels (on edges that have secondary bevels) are much more difficult to stablilize and 'feel' when honing or stropping; more so, if your edge angles are relatively high (wide) at or beyond 40° inclusive. Wider (more obtuse) edge angles will make the bevels even narrower, for a given blade/edge thickness. That's likely what you're having trouble with, as previously mentioned. There may also be issues with too much pressure used on the narrower bevels, which can also aggravate edge-rounding on softer strops of leather or thicker fabrics.

An alternative is to profile your edges at a lower angle to a 'zero edge' or 'zero grind', on which the primary grind of the blade, or a significant portion of it, is essentially honed directly to a sharp apex, with no distinct, narrow secondary bevel behind the edge. Done this way, it's much easier to feel larger expanse of the primary grind on a hone or strop (because the blade is held to a much lower angle), and thin edges can be honed to extreme sharpness pretty easily. Usually, in the absence of distinct secondary bevels, some convexity will result near/close to the edge, unless the whole blade is laid dead-flat to the hone or strop. That being said, the lower honing angle makes stabilizing the blade much easier. The pic below is an illustration of a lowered approach on one of my knives (Buck 301 folder), showing the resulting convexed & polished portions which replaced the factory edge bevels, which were obviously narrower. In the pics, the shiny portions near the edge may look like wider bevels, though there's no longer a distinct 'shoulder' on them.

PB200033_zpsde779182.jpg

PB200030_zps02e95c5b.jpg



David
Click to expand...

so get rid of the secondary grind all together and make it a true flat grind? That's not a bad idea. it'll be way easier to sharpen...that's for sure.
 
samuraistuart said:
I sorta get where the OP is going with this, I think. Thin spines, and super thin edges (.005" and under), just don't have that same feel as a thicker edge does when you take that apex to your fingertips. It may be just simply there is more mass in the thicker edge, so that translates better to your sense of feeling in your fingertips. But take that thin knife and cut thru cardboard, and there is no question, it's wicked sharp and the thin geometry allows for an efficient cut. Sort of like a blade on a safety razor vs the edge on a chef's knife that has a .010" edge before sharpening. Yeah, no question the razor is sharp, but that relatively "large" edge bevel on the chef's knife just feels sharper on the fingers (when sharpened well)....to me anyway.
Click to expand...

This is also something I had considered. Maybe it is just as sharp, it just doesn't feel like it? I wasn't sure if that was even possible, but it sounds like im not the only one with this problem.
 
jamiesaun said:
so get rid of the secondary grind all together and make it a true flat grind? That's not a bad idea. it'll be way easier to sharpen...that's for sure.
Click to expand...

Either flat or convex (mine finish out with at least a little convex where the 'bevels' would otherwise be); either one becomes much easier to sharpen & maintain, with the larger area of contact on the sharpening media. If you still want a more robust edge angle, a microbevel applied after sharpening the primary can be done in just a pass or two on each side, minimizing opportunity for error.

Over time and with more practice, you might eventually find a hold that suits your hands for comfortable and consistent angle control. Doesn't necessarily matter what the actual angle will be specifically; only that it becomes more repeatable, after which you'll find it easier to produce more consistent-looking bevels and crisper edges. That's what I finally figured out and settled into with a lot of experimentation and repetition; I've found my 'comfort zone' to be in a ~25° inclusive ballpark, sometimes lower. It makes freehand sharpening much more intuitive and easy, when your adopted method just 'feels right' and is natural to you; and that will be developed with repetition over time.


David
 
Awesome. Yeah, with a big knife, it's easy to keep a bevel straight and consistent. With a thin knife, it's a lot tougher. I'm now positive this is the problem I'm having.

Thanks
 
When I started sharpening my Boker Congress Carver, I discovered that my intended angles on a couple of the blades were within a degree or two of the primary grind. So, I just laid that sucker flat and went after it. After enough edge polishing, it will push cut end grain hardwood like butter.
 
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