Thinning Hollow Grind Blades?

[pinnah]

Seeking advice on the advisability and method to thin hollow grind blades.

I do a lot of camping. For my needs, the 2 most important uses of my knives are for food prep and cutting wood shavings for fire starting.

By far, the best performing knives for this are my Opinels. Problem is, emotionally I love Buck knives. But compared to my Opinels, well, there's just no comparison for food prep and wood shaving.

I've observed that among my Buck knives, those with the thinnest blade and the least amount of "shoulder" to the hollow grind do the best (e.g. 500 or 482 compared the thicker blades 110 and 112).

Would thinning the spin and unground shoulder of the hollow grind improve the cutting performance of a knife like the 110 or 103?

If so, what the best way to do it with out power tools?

Note, I'm aware that a big part of the cutting performance of the Opinel comes from the full convex grind and I know I'm not going to create that on a 110 or 103.

Thanks for any guidance

 

[shecky]

I've reprofiled a few hollow ground blades by laying the grind flat against a stone so that the top of the grind and the top of the edge bevel rest on the stone. Then grind away. My aim is for a zero edge (no separate edge bevel). This does alter the look of the blade, and the hollow ends up much smaller, or even gone. But the result is a blade that slices better, has a usable edge for longer, and is easier to sharpen.

 

[Obsessed with Edges]

You might not need to actually 'thin' the shoulder of the hollow grind much at all. Just round off or smooth it out, so there isn't a hard edge there. That abrupt corner at the very shoulder of the grind is what makes most of the difference in resistance to slicing.

If you really must thin it out though, shecky's suggestion above is straight & to the point. Either on a stone, or use wet/dry sanpaper on a hard backing, like glass. Just lay the blade flush to the abrasive (contact at both the edge bevel and the hollow's shoulder), and grind away.

Personally, I don't think I'd worry too much about the shoulder of a high hollow grind anyway, unless there's a huge taper in the blade (very thick spine). On a hollow grind, the thinness of the edge itself will make most of the difference. Re-bevelling to a thinner edge angle is what I'd normally do, and this is especially simple on a hollow grind, as there's not much metal to remove near the edge. Doesn't take long.

 

[pinnah]

Thanks for the input guys.

A few bits of clarification...

First, if I want to soften the shoulder on the high hollow grind but want the cutting edge to be convex, instead of a 0-edge/full flat, do I guess that the trick is to get the angle just so the edge is off of the stone as I work on the shoulder? Did I just get an advanced degree in "duh!"?

Second, is spine thickness an issue? My Opinel #10 is approx 2.5mm thick at the spine. My Buck folder measure about 3.0mm. Measurements taken with a crude caliper. The Opinel goes through veggies and wood marvelously. The Bucks have a tendency to bind up in both. Even with the shoulder of the hollow grind softened, am I right to think that thinning the spine will also help? Or, not so much?

Third (thread drift and more of comment/follow-up for OWE/David on a thread from the traditional forum)... David, I've been playing with your suggestion to convex the edge of the hollow ground Bucks. I'm using sharpie as a way of getting feedback. I'm looking to take material off of the shoulder of the cutting edge with progressively higher grits of paper on my strop board, yes?

 

[Obsessed with Edges]

Thanks for the input guys.

A few bits of clarification...

First, if I want to soften the shoulder on the high hollow grind but want the cutting edge to be convex, instead of a 0-edge/full flat, do I guess that the trick is to get the angle just so the edge is off of the stone as I work on the shoulder? Did I just get an advanced degree in "duh!"?

Actually, this makes it easier. You can soften the hollow grind's shoulder and convex the shoulder of the edge bevel simultaneously, simply by doing your sanding/grinding on a softer backing, like leather. This is often the exact result I get in convexing some of my blades on my sandpaper/strop block combo. I do it for the sake of the edge, but oftentimes end up taking some material from the shoulder of hollow/sabre grinds in the process.

Second, is spine thickness an issue? My Opinel #10 is approx 2.5mm thick at the spine. My Buck folder measure about 3.0mm. Measurements taken with a crude caliper. The Opinel goes through veggies and wood marvelously. The Bucks have a tendency to bind up in both. Even with the shoulder of the hollow grind softened, am I right to think that thinning the spine will also help? Or, not so much?

I wouldn't be too concerned about spine thickness here. 3.0 mm isn't all that thick (at least in my view). I have an older A.G. Russell folder, which features a full-height hollow grind up to a ~ 5mm spine thickness, on a blade that's about 19-20mm wide, edge to spine. That's what I'd call extreme. Even on that one, just thinning the edge bevel itself, to a more acute angle, made a huge difference in slicing. I haven't worried about trying to thin the spine on that one (it has a certain beauty in itself ).

Third (thread drift and more of comment/follow-up for OWE/David on a thread from the traditional forum)... David, I've been playing with your suggestion to convex the edge of the hollow ground Bucks. I'm using sharpie as a way of getting feedback. I'm looking to take material off of the shoulder of the cutting edge with progressively higher grits of paper on my strop board, yes?

That should work fine. Depending on what grit you'd prefer to finish at, I'd start with the higher grit first. You might be surprised at how little aggressiveness it takes, just to smooth off the shoulder of the edge bevel. I first started noticing how simple this was, when I was regularly using 1000/2000 grit paper to touch up my edges. It really doesn't take much at all, especially on a thin hollow grind's edge. If you prefer to finish at a slightly 'toothier' grit, then something in the 400 - 800 range should work well. Again, try the higher end of that range first, if that's appropriate for the finish you want.

 

[Rapt_up]

Thanks for the input guys.

A few bits of clarification...


Second, is spine thickness an issue? My Opinel #10 is approx 2.5mm thick at the spine. My Buck folder measure about 3.0mm. Measurements taken with a crude caliper. The Opinel goes through veggies and wood marvelously. The Bucks have a tendency to bind up in both. Even with the shoulder of the hollow grind softened, am I right to think that thinning the spine will also help? Or, not so much?

The thing with hollow grind is that they give you nice and thin near the vcutting edge but are less good for full depth plus slicing. (kitchen style) because they have very low resistance to slicing at first but have a big increast right near the end of the cut when you are trying to wedge apart the cut material mroe abruptly as you drive the last bit and the spine through the cut material.

In general terms with a flat grind the force is more uniform, as the "wedgoing" doesn't change angle, with a convex you do most of the "wedging" close to the cut and then additional depth makes less difference.

 

[pinnah]

So, a quick update on some progress. Also want to parrot back what I think I'm hearing to confirm that I'm understanding things correctly...

UPDATE - Spent most of yesterday on conference calls so while the mindless buzzing noise in my ears tried to drain every last bit of sanity from my brain, I had the chance to work on the Buck 112 and Case 316-5 on the strop with some 800 and 2000 grit paper as described above. Actually, the 440C 112 spent a bit of time on 400 grit. I used magic marker and magnification and was able to confirm/keep the work on the shoulder of the cutting edge.

This morning, I spent a few minutes before work going after some sticks with the tuned up 112 and 316-5 next to my Opinel #10. Huge improvement. The Opinel still "hooks up" in the wood more easily and seems to peel off curled shavings with greater ease. It also feels much easier to control the depth of the cutting. But still, the 112 and 316-5 are much, much better and producing curled shavings.

As fate would have it, a buddy at work brought by one of his wood working books: "Whittling Twigs and Branches" by Chris Lubkemann, which discusses how to create figures like roosters that use fanned curls extensively. Think feather stick meets primitive art. In his section on blades, Lubkemann notes that neither sharp shouldered factory edges (like those created by my Lansky system) nor pure flat edges (preferred by many wood workers, it would seem) are ideal for producing fanned curls. Instead, he suggests a beveled edge which has had it's shoulders rounded - in short, a convexed edge. His preferred sharpening method to get this is wet/dry paper on wood/leather backing. Sounding pretty familiar.


CONFIRMATION - Here's my understanding of what's going on, mostly from OWE's excellent and very helpful post in the Traditional Forum where I first raised my questions (thanks, Dave!). As I understand it, there is a primary and a secondary issue. Would love to hear confirmation that I'm on the right track....

Primary Issue: When using a guided system like the Lansky (which I use), it is likely to produce a sharp, crisply defined shoulder to the cutting edge. This problem is more pronounced on hollow ground blades than it is for convex ground blades assuming the same sharpening angle since the thinner blade (above the cutting edge) of the hollow grind will produce a more acute angle at the edge shoulder. This crisp, sharp shoulder on the cutting edge can cause drag when cutting wood or vegetables and thus either bind or tear the cut material.

Secondary Issue 1 (more speculative on my part): With my 1095 Opinels which have a convex blade grind, stropping alone (Simicrhome on leather) would be enough to "soften" the shoulder of the cutting edge. With my 440C 112, stropping alone (Simicrhome on leather) would not be enough to round out the shoulder of the cutting edge, but stropping on wet/dry paper on leather (800/2000 grit) would be.

Secondary Issue 2: Even with similarly convexed cutting edges, the convex grind of the Opinel will tend to out perform hollow grind blades for this kind of cutting due to the "splitting wedge" function of the convex grind. But, this gap can be closed considerably if the cutting edge of the hollow ground blade is properly convexed at the shoulder of the cutting edge.

So... am I getting closer to understanding this right?

 

[Obsessed with Edges]

So, a quick update on some progress. Also want to parrot back what I think I'm hearing to confirm that I'm understanding things correctly...

UPDATE - Spent most of yesterday on conference calls so while the mindless buzzing noise in my ears tried to drain every last bit of sanity from my brain, I had the chance to work on the Buck 112 and Case 316-5 on the strop with some 800 and 2000 grit paper as described above. Actually, the 440C 112 spent a bit of time on 400 grit. I used magic marker and magnification and was able to confirm/keep the work on the shoulder of the cutting edge.

This morning, I spent a few minutes before work going after some sticks with the tuned up 112 and 316-5 next to my Opinel #10. Huge improvement. The Opinel still "hooks up" in the wood more easily and seems to peel off curled shavings with greater ease. It also feels much easier to control the depth of the cutting. But still, the 112 and 316-5 are much, much better and producing curled shavings.

As fate would have it, a buddy at work brought by one of his wood working books: "Whittling Twigs and Branches" by Chris Lubkemann, which discusses how to create figures like roosters that use fanned curls extensively. Think feather stick meets primitive art. In his section on blades, Lubkemann notes that neither sharp shouldered factory edges (like those created by my Lansky system) nor pure flat edges (preferred by many wood workers, it would seem) are ideal for producing fanned curls. Instead, he suggests a beveled edge which has had it's shoulders rounded - in short, a convexed edge. His preferred sharpening method to get this is wet/dry paper on wood/leather backing. Sounding pretty familiar.

You've been busy! And it looks like it's been productive and enlightening as well. :thumbup:

CONFIRMATION - Here's my understanding of what's going on, mostly from OWE's excellent and very helpful post in the Traditional Forum where I first raised my questions (thanks, Dave!). As I understand it, there is a primary and a secondary issue. Would love to hear confirmation that I'm on the right track....

Primary Issue: When using a guided system like the Lansky (which I use), it is likely to produce a sharp, crisply defined shoulder to the cutting edge. This problem is more pronounced on hollow ground blades than it is for convex ground blades assuming the same sharpening angle since the thinner blade (above the cutting edge) of the hollow grind will produce a more acute angle at the edge shoulder. This crisp, sharp shoulder on the cutting edge can cause drag when cutting wood or vegetables and thus either bind or tear the cut material.

Secondary Issue 1 (more speculative on my part): With my 1095 Opinels which have a convex blade grind, stropping alone (Simicrhome on leather) would be enough to "soften" the shoulder of the cutting edge. With my 440C 112, stropping alone (Simicrhome on leather) would not be enough to round out the shoulder of the cutting edge, but stropping on wet/dry paper on leather (800/2000 grit) would be.

Secondary Issue 2: Even with similarly convexed cutting edges, the convex grind of the Opinel will tend to out perform hollow grind blades for this kind of cutting due to the "splitting wedge" function of the convex grind. But, this gap can be closed considerably if the cutting edge of the hollow ground blade is properly convexed at the shoulder of the cutting edge.

So... am I getting closer to understanding this right?

I think you're on the right track, i.e. you seem to be seeing results consistent with my impressions, on all points listed above. I'm especially encouraged to see you're noticing the real benefit of smoothing/rounding the shoulder of the V-bevel. It really opened my eyes, when I noticed it, especially considering how little modification is needed to make that huge difference in cutting resistance.

Edit:
One very minor (trivial) point. Opinel uses a steel called 'XC-90' (apparently a French recipe) for their carbon blades. It isn't 1095 (by name), but seems very similar in composition. Very basic stuff, 0.8 - 1.05% carbon content, and small traces of some other elements. Essentially nothing to form any hard carbides, so it'll sharpen up/shape/sand very easily, consistent with what you've seen. In other words, very (very) much like 1095.