Convex Sharpening Confusion

[Shamshir]

Hello,

I'm a bit confused about convex sharpening and cannot reconciles the variety of things I've read. Your assistance is much appreciated.

Here are some facts about my situation
- Knife: BRKT Gunny Hunter A2.
- Experience: Novice
- Device: I've chosen sandpaper over soft backing rather than stones+rolling the wrist
- Before using sandpaper, I'm trying green compound on leather + sharpie to practice
- ~7oz leather glued to a board

Here's the crux of the confusion. I've marked the blade with a sharpie to see how things go. If I lay the knife flat and raise it until there is no shadow and strop, only the marker on the blade/shoulder is cleared. The very edge is still black. In order to get the edge (extra polished shiny part of the zero convex OR the micro bevel?!), I have to raise the knife to "Bite Angle" (i.e. where I counter-strop raising the angle until the knife bites, then lower the angle a tad and strop).

I've attached 3 images:
- How thick the leather is, how thick a mouse pad I have is (maybe use this? Or get a thicker squishier one?)
- The lower angel (where the marker on the blade is cleared)
- The higher angel (where the marker on the edge is cleared)

So....

- In order to lay the knife flat (low angle) should I be using a 1/4" mouse pad (from early 90's) instead of the leather?
- To maintain a full convex, Should I use a higher angel for the edge and a lower angel for the blade/shoulder? If so, then where is the "easy convex" soft backing trick?
- Is it that the blade isn't zero convex?
- Do I need to roll my wrist (in which case, might as well jump in the deep end and try stones for convex?)

What am I doing wrong? Or what have I got wrong? My impression was that for convex, a soft backing would be used and then most of the blade and edge would be kept "in-line", sharpened/ground-off uniformly.

Thanks again,
Shamshir.

 

[bucketstove]

Hi Shamshir,
what grit sandpaper are you using?
what are you using for lube?
how long are you sharpening, how many strokes?

from the picture first picture, a solution could be as simple as, push harder, and you'll be reaching the apex

 

[DeadboxHero]

Long story short, there is a microbevel preventing you from reaching the apex,

The Gunny has a thin blade stock which makes a very acute geometry. For wood carving, I recommend raising it like in your second picture and grind away until both sides are even, then stick with one side until a burr is formed, etc.

You can then blend the convex by lowering the angle for a uniform finish.

 

[method_burger]

I do a wrist roll while sharpening, and I mount the strop at an angle (with small wrist rolls, this is to strop the convex portion easier). I only do one part of the edge at a time, straight down the strop, instead of along the length of the knife, and because it is slightly mounted, the whole bevel is stropped. I like to pull towards myself for convex, so the strop is mounted slightly higher towards me. This is based on no microbevels, because if there was a microbevel, I would just strop that part. And my strop is not very soft, but I think that is more preference than anything else.

Also, before you strop, try to deburr and cut paper or whatever. It might be that from the factory, it came with a microbevel, and you haven't sharpened that away. (not sure because I never owned a gunny hunter) If it cuts, to a somewhat satisfactory degree, then you should strop. If it doesn't cut, keep sharpening. But information about what sandpaper grit you use would be helpful.

 

[Danketch]

From my experience with Bark River's, a lot of them have a high shoulder, prevent a true zero-degree convex. That shoulder needs to be ground down first, to get it sharp. I used mainly a DMT duo-fold to get it there, but waterstones or a silicone carbide stone would get it there at well. I gave up on the mouse pad/sandpaper deal, a long time ago, as I found it was too easy for me to round the apex over. This may be the case for you as well. For me its easier to sharpen convex edges on a harder backing than a softer one, and it seems its easier to control the angle/edge I want as well.

Basically, what deadbox said, but use a harder substrate, as you might be rounding the edges too soon.

 

[Obsessed with Edges]

Soft backing is easy for a beginner in convexing, but not very good for creating or refining the apex.

Firmer backing can also be easy, and much, much better at both creating and refining the apex.

Wherever it originated, I really believe the notion of using a mousepad for convexing was a very bad idea, creating more problems that it solves. True, it does make it 'easy' for creating the bigger convex of the primary grind on a blade (above the edge). Leather backing can sometimes be marginally better, depending on how firm or thin it is. But beyond that, a softish backing will just be an obstacle in the way of the aggressive grinding needed to form a crisper apex, and it'll also be detrimental to maintaining a crisp apex, tending more towards rounding it off instead. Going too-soft under the sandpaper just allows the paper to roll around the apex, which rounds it off and also doesn't exert the firm pressure necessary to crisply shape the edge.

For a beginner considering soft or hard backings under the sandpaper, there's a better 'middle ground' solution for creating convexes and keeping them sharp. Instead of doing it over a mousepad or leather, use only a couple or three sheets of plain paper underneath the sandpaper to initiate the convex. That still gives enough 'cushion' to easily form it, but will still be firm enough to shape and refine the edge so it's starting to get sharp. As you get closer to being 'sharp', REMOVE a sheet of paper (or two) under the sandpaper, then refine some more. Eventually, you want to get to a point where you're using ONLY the sandpaper over a firm/hard backing (wood, glass, stone, etc) to refine the apex, which will leave it in much, much better shape. Developing a feel for doing this on a hard backing will naturally train the hands for transitioning to stones for this as well. In terms of faster grinding and forming the crispest edges possible, a stone will do it better than anything else. This isn't to say you can't get good results in that 'middle ground' though, using the sandpaper over a very firm (at least) backing with steadily-improving skills.


David

 

[cbwx34]

From my experience with Bark River's, a lot of them have a high shoulder, prevent a true zero-degree convex.

Yup, me too. The "confusion" is because Bark River pretends this isn't true.

I agree a firmer backing is better. Soft backing or pushing hard will only make it worse. You can sharpen similar to what Murray Carter recommends (he has videos on YouTube)... not using a waterstone necessarily, but the concept of work the main part of the blade to thin it, then raise the knife slightly and establish the edge. (You can do it with sandpaper/leather to keep a convex profile, or whatever you decide to use.)

Edit: You might also want to check out the Stropping-angle-plus-pressure thread.

 

[Shamshir]

Thanks for your input everybody. This is great feedback.

Some follow up questions:

~~~~~~~~~~

bucketstove,

I haven't started using sandpaper yet. I figured I'd just try polishing off marker so I can see what's happening with the angles.

~~~~~~~~~~

DeadboxHero,

So your recommendation is for me to keep something close to the current edge angle (higher angle), sharpen/maintain the edge at that angle, but also to blend it better with the rest of the blade by using lower angles (like my 3rd picture) too?

~~~~~~~~~~

method_burger,

It's sharp enough to cut printing paper, but not a lot better than that.

~~~~~~~~~~

Obsessed with Edges.

Regarding your 'middle round' solution. Glad you mentioned it. This touches on something I read often but never figured out. A few papers that would provide even less curvature than the leather... so what's the idea? Is it that we want just a bit of "give" so that the very edge is curved? Outside of a small curvature the papers would offer, I still have to roll my wrist or manage multiple blended angles to maintain convex. Yeah? So what advantage does it give over hard stone?

~~~~~~~~~~

cbwx34,

Yeah, I've seen that video... aspirational. I bought a Svord Peasant to round off into convex and practice convex maintanance on stones. I figured in the meanwhile, I'd handle the gunny with a more forgiving method. But based on this discussion, perhaps I'll race towards stones faster.

~~~~~~~~~~

All in all...

What I'm getting is that soft backing can round my edge and doesn't help a whole lot with a convex geometry. So, with that draw back in mind, and since I have to manage multiple angle, why wouldn't I just focus and practice on wetstones? What advance is the leather backed option have over the stones?

And finally, when rolling my wrist on a stone, is there a trick to help not raise the angle too high (beyond the apex)? Or is it just an art my bones have to learn?


Thanks again.

 

[Obsessed with Edges]

"Obsessed with Edges.

Regarding your 'middle round' solution. Glad you mentioned it. This touches on something I read often but never figured out. A few papers that would provide even less curvature than the leather... so what's the idea? Is it that we want just a bit of "give" so that the very edge is curved? Outside of a small curvature the papers would offer, I still have to roll my wrist or manage multiple blended angles to maintain convex. Yeah? So what advantage does it give over hard stone?"

The main advantage is in giving just enough cushion for the convex to form easily, without too much 'give' which tends to round off the edge. That little bit of cushion is often what 'feels easier' for a novice starting out, without needing to deliberately 'roll' the wrist. No real advantage in terms of the edge it'll produce, as compared to using a stone. But the stone, or using the sandpaper only over a hard backing like glass, will produce a crisper (therefore sharper) edge overall, if the user is up to doing it that way.

There generally will be less curvature with a firmer backing, assuming the hand is pretty steady. But a shallower convex is almost always a better thing anyway, in terms of helping the edge stay crisp.


David

 

[HeavyHanded]

All in all...

What I'm getting is that soft backing can round my edge and doesn't help a whole lot with a convex geometry. So, with that draw back in mind, and since I have to manage multiple angle, why wouldn't I just focus and practice on wetstones? What advance is the leather backed option have over the stones?

And finally, when rolling my wrist on a stone, is there a trick to help not raise the angle too high (beyond the apex)? Or is it just an art my bones have to learn?


Thanks again.

The only advantage to using conformable backings on your convex is cosmetic - it is a lot easier to get it looking nice. When it comes to shaping the edge especially if its a very shallow convex, working with a hard stone or at the most sandpaper over a very hard surface will give you a lot more control.

You can run the Sharpie lines radially - from spine to edge all the length and this will show exactly where you're hitting. Once you get a feel for it, the feel of the apex on or just about to start catching, you'll find sharpening convex on a hard stone is easier than sharpening a V bevel on a hard stone...except for the cosmetics.

Once its good and set, you'll find maintaining a good geometry on full convex is very easy with a leather strop but can also be done on your hard stone, balsa strop etc - anything you might use for a flat bevel.