Sharpening Dual Grit Edges

[The Home Slice]

Hey Spyderco community, my name is Gabe (YouTube Creator from The Home Slice channel) - and I have popularized a style of sharpening called "Dual Grit". I am brand new to the Forum scene, so feel free to notify me how things work here if I am out of normal protocol at any point.

In Dual Grit Sharpening, you sharpen the first side of the edge with a coarse stone, and work the second side of the edge up to a fine stone, leaving the 2 edge finishes combined at the apex. Usually, the edge forms best using all edge-trailing strokes, and some stropping is often required to clean up the edge from unhelpful amounts of burr.

My Preferred Sharpening Gear for Dual Grit Edges at the time of this entry are:

• Coarse Side - 250-400 grit CBN or Diamond plate (e.g. Spyderco, or DMT) for high aggression, though Norton Crystolon Coarse (SiC) works well too, especially for more conventional/lower carbon steel, or thinner edges

• Fine Side - Soft water-stone (using SueHiro Cerax 3K atm, also good results from King 6K) OR fine resin-bonded/OCB diamond water-stone (e.g. Venev) on steel with more than 3% Vanadium)

• Strop - I do 3-10 strokes on flat denim loaded with Mother's Mag & Aluminum polish for low-mid Vanadium steels, and 30+ light strokes of fine (sub 1 micron) diamond on flat leather for high Vanadium Steel

• Note: I have also had very good aggression results from UltraFine Ceramics (Spyderco, Fallkniven) on fine side of edge, but these seem to require a little more stropping to remove fine feather-burr

Dual Grit sharpening was first thought to create micro-serrations, but Dr. Todd Simpson's wrote an article (using some samples I sent to him) discovering that the edge dynamics are very complex, including an extended apex that is heavily textured and thinner than the sharpened edge angle, but still durable enough for most everyday strains (I will try to link the full article in thread).

The sharpening method seems to extend working-edge functionality and aggression significantly (the most outstanding test result to date being a roughly 50% increase in wear resistance in Pete's CPM MagnaCut test - link in thread). However, as all things are a trade-off, it seems that this long lasting aggression may come at a cost of slightly reduced push-cutting/shaving efficiency and a slightly less durable apex for impact tasks (at least in my testing so far).

The most up-to-date picture of my sharpening method right now is also linked in thread if you want more specifics, and I am working with the folks at Spyderco to conduct testing on a range of different steels in an effort to find sharpening protocols that are optimized for each specific category of steel, and perhaps some specific steels that benefit from one particular method, stone, or abrasive combination.

I have created this topic to offer what knowledge I have to anyone on the forum, and I am most happy to respond to questions (sharing what I do and don't know).
This is a place for people to share their experiences, ideas, and questions - so that I/we can troubleshoot how to get the longest possible life out of your knife edges for the least work.

Fire at will...

[benja-man]

Hey, cool to see you having joined the forum to share some of your knowledge :-)

Personally I suck at sharpening, gave dual grit only one try using a sharpmaker and a serrated knife without any success. So still getting my skills up with conventional methods.

[Urkilnmesmalls]

Good to have you here Gabe! I have dabbled in the dual grit edge myself in the earliest days of your YouTube channel. I found it impressive, but I haven’t kept up with it due to laziness when it comes to sharpening lately. One stone and a couple swipes on the stop for me lately. I might need to try it again. I bet cruwear responds amazingly to it.

[Scandi Grind]

Cool, nice to have you aboard! I might have to try this general technique sometime.

[The Home Slice]

As promised - the links I referred to:

• Science of Sharp article by Dr. Todd Simpson -
  https://scienceofsharp.com/2021/06/15/d ... harpening/

• Best Dual Grit Test on Pete's channel (Cedric & Ada Outdoors) -
  https://youtu.be/bvPdb-n3__Q

• The closest video to my current experimental method:
  https://youtu.be/1wSgNNs2ISU

[The Home Slice]

Hey, cool to see you having joined the forum to share some of your knowledge :-)

Personally I suck at sharpening, gave dual grit only one try using a sharpmaker and a serrated knife without any success. So still getting my skills up with conventional methods.

Thanks for the response!

IMO no one sucks at sharpening, you may just need a piece of knowledge or two to get to the next level. Knowing what to look for in your edge or sharpening experience turns practice into skill; I'd encourage you to continue with learning conventional methods. If you consistently hit a certain roadblock, please feel free to share what it is and if I've been there and have any tips I'd be happy to share. You can even send me a private message if you don't want to spam up one of the forum threads.

Cheers.

[The Home Slice]

Good to have you here Gabe! I have dabbled in the dual grit edge myself in the earliest days of your YouTube channel. I found it impressive, but I haven’t kept up with it due to laziness when it comes to sharpening lately. One stone and a couple swipes on the stop for me lately. I might need to try it again. I bet cruwear responds amazingly to it.

Aw, that's all good man - glad you got to try it early on. I myself am alternating between fine and dual grit at the moment in an effort to ascertain the differences.

And the only thing that keeps me from "sharpening laziness" is a few subscribers who are depending on me to do my homework, and who provide critical feedback when I slack off Hahahaha

With regards to CruWear, I currently have the BladeHQ "Cru-Carta PM2" as it is endearingly called. I have so many stones and steels at present, I cannot promise I will remember to give an in-depth review of dual-grit Cru-Wear, but I certainly plan to update the forum and the channel with an overview of what steels and stones work best once I get through testing both low and high carbon in stainless and tool steels.

Cheers,

[The Home Slice]

Cool, nice to have you aboard! I might have to try this general technique sometime.

Let me know how it goes if you do - or if you run into any problems. My video tutorial is now in a link just after your comment, so you can check it out if that's helpful!

Cheers,

[Urkilnmesmalls]

Good to have you here Gabe! I have dabbled in the dual grit edge myself in the earliest days of your YouTube channel. I found it impressive, but I haven’t kept up with it due to laziness when it comes to sharpening lately. One stone and a couple swipes on the stop for me lately. I might need to try it again. I bet cruwear responds amazingly to it.

Aw, that's all good man - glad you got to try it early on. I myself am alternating between fine and dual grit at the moment in an effort to ascertain the differences.

And the only thing that keeps me from "sharpening laziness" is a few subscribers who are depending on me to do my homework, and who provide critical feedback when I slack off Hahahaha

With regards to CruWear, I currently have the BladeHQ "Cru-Carta PM2" as it is endearingly called. I have so many stones and steels at present, I cannot promise I will remember to give an in-depth review of dual-grit Cru-Wear, but I certainly plan to update the forum and the channel with an overview of what steels and stones work best once I get through testing both low and high carbon in stainless and tool steels.

Cheers,

I have that same blade. I might give it a try myself. I recall I did 140 on one side and up to 8000 on the other side and I really got a lot of use out of s30v

[WyoJon]

This is really interesting. I like the idea. I have long practiced sharpening edges heel to toe, and toe to heel, to get the teeth in both directio s with much success.

[WyoJon]

Hey, cool to see you having joined the forum to share some of your knowledge :-)

Personally I suck at sharpening, gave dual grit only one try using a sharpmaker and a serrated knife without any success. So still getting my skills up with conventional methods.

Thanks for the response!

IMO no one sucks at sharpening, you may just need a piece of knowledge or two to get to the next level. Knowing what to look for in your edge or sharpening experience turns practice into skill; I'd encourage you to continue with learning conventional methods. If you consistently hit a certain roadblock, please feel free to share what it is and if I've been there and have any tips I'd be happy to share. You can even send me a private message if you don't want to spam up one of the forum threads.

Cheers.

Using a jewelwers loupe to watch what is happening helped me a lot.

[kennbr34]

It's an interesting concept, but what immediately comes to mind for me is that I touch my knives up on a pocket hone a lot, and it seems like it would undo the dual finish.

Having quickly read Todd's article I am curious about how the ductility of the steel would affect the virtues of this method.

I'm not sure if I am drawing the same conclusions as Todd, but it seems to me that the primary mechanism of improvement here is a secondary burr created at the end of the first which is absorbing much of the deformation that the first burr would normally see. This is allowing the first burr to remain relatively unscathed compared to how it would be affected without the secondary burr to protect it. Then, because what we essentially have is a protected wire edge, it results in a geometry at the apex which is thinner than it normally would be, allowing for more edge retention.

I'm curious about ductility because I wonder how much plastic deformation specifically in the secondary burr is the performative factor here. Similar to crumple zones in car wrecks, for example. By taking the force and deforming, it's absorbing energy that would normally be transferred directly to the main burr, which we all know does not react well to that. I'm suspecting that the secondary burr is essentially acting as a cushion, drastically reducing the force imparted on the main burr and allowing it to maintain its geometry much longer than it normally could.

If my assumption is correct, I would expect this method to benefit softer/tougher steels more. As the ductility decreases I would suspect it to shatter and chip rather than deform plastically. That would still lead to an observable increase in edge retention as the shattering of the primary burr would still be absorbing energy transferred to the primary burr, but I think a secondary burr that is ductile enough not to shatter will absorb more energy, as well as lead to less damage to the primary burr supporting it since chips tend to migrate along grain paths and take out larger portions of the underlying structure.

If one was to compare the result of one particular knife before and after dual grit sharpening, I suspect the improvement will be more dramatic for tougher/softer steels which possess more ductility. Or in other words, steels with high carbide volume or ultra hard heat treatment might not see as dramatic improvements.

Those Victoronix pairing knives are pretty soft, fine-grained steel are they not? I would be really curious to see the images examining some high-handedness and/or high-carbide steel. My guess is that they would show a lot more damage to the primary burr as a result of the secondary burr chipping/shattering. Going by Larrin Thomas's articles on edge stability, anyway.

Anyway, take my thoughts with a grain of salt, since I have absolutely zero qualifications as a metallurgist. But from spending way too much time reading Larrin Thomas's and Todd Simpson's blogs, that's my take on this.

[u.w.]

Hey Gabe,
Welcome to the forum! I've enjoyed many of your videos; and, Thank You for taking the time and sharing.
I've oft wondered if your "dual grit edge" is the just the "fine side" being a good de-burrer of the coarse side burr, thereby getting closer to, or better achieving, a burr-free apex?
Based on the videos you and Pete have put the time into and shared, it (your dual-grit edge) seems to be a good edge. Thanks again for putting in so much time and sharing your data/findings.

u.w.

[The Home Slice]

A) It's an interesting concept, but what immediately comes to mind for me is that I touch my knives up on a pocket hone a lot, and it seems like it would undo the dual finish...

B) It seems to me that the primary mechanism of improvement here is a secondary burr created at the end of the first which is absorbing much of the deformation that the first burr would normally see. This is allowing the first burr to remain relatively unscathed compared to how it would be affected without the secondary burr to protect it.

C)I'm curious about ductility because I wonder how much plastic deformation specifically in the secondary burr is the performative factor here. If my assumption is correct, I would expect this method to benefit softer/tougher steels more.

Love your thoughts - it's great to hear from another KnifeSteelNerds/ScienceOfSharp fanatic! I'm gonna try to respond to the main thoughts in your post.

A) Yeah, dual grit is more of a "setting the edge" kind of thing - for longest lasting aggressive working edge. A pocket hone (Spyderco Ceramic or similar I assume?) would likely remove the effect almost instantly. Which is not to say you can't touch up a dual grit edge. If you try dual grit, I'd recommend:

• Set the edge with your coarse and fine stones (try finishing with edge trailing strokes), strop with a compound which you are comfortable with if you have one.

• Use until you don't like the performance, then realign on unloaded leather to bring it back to keen.

• When desirable performance can no longer be reached, it's usually because you've worn down to the base of that extended burr, or (in rare cases) broken it off, but at this stage your apex is still not very wide (Todd estimated the base of the large burr to be about 3 microns in most places) - so you can still use a couple strokes on a pocket hone to return it to functioning surprisingly easily.

Just my thoughts from my experiences with dual grit.

B) I do think that the burr-making/deburring tendencies of the 2 stones do work together in dual grit edges. I had not thought of it as 2 separate burrs, but I can follow your line of thought. From what I understood from the article and subsequent conversations, I believe that the long lasting edge retention comes from a combination of things - with 2 of the main ones being

• That it takes little force to initiate cuts due to the aggressive coarse texturing at the apex and the thinner geometry of the extended apex leading to less edge-damaging force being applied for the same amount of work.

• The edge apex abrades more slowly due to the edge extension having a section which remains at nearly constant/fixed thickness (IE the large burr is around 7-10 microns in height but remains just under/around 3 microns thick over that length, leading to the working edge performance of the apex being relatively "frozen" at that thickness until the apex extension is worn away).

That is the best way I have to understand it at present anyway. I do not know if the burr has a distinct secondary burr which acts like a shock absorber, that's an interesting thought! I have experienced that dual grit edges are not the best for high shock and impact work like chopping, due to the thin-ness of the apex.

C) I do think higher ductility steels often experience a larger performance increase with a dual grit edge. I have tried dual grit with lots of steels, and the main "flop" which I have experienced was Maxamet, with dual grit performing much more like a wire edge. That said, my methods (particularly burr-minimization and stropping) were not very good at the time when Pete performed that test, and we may be able to get better results.

The successful tests which Pete has done have all shown roughly a 50% increase in observed edge retention, and the lowest toughness steel to still gain that much retention was Benchmade's M390. I suspect (and anecdotally observe) that for the best edge-retention increase, the steel needs enough Carbon and Hardness for that large burr to stand firm and not bend over (blind guess I'd estimate more than half a percent of Carbon and more than 57 HRC), but the benefit seems to begin to be reduced when there are many carbides touching inside the steel, because when the apex steel is moved, voids form between carbides (like in Todd's S110V article part 3) weakening the dual grit edge.

I find exceptional results with LC200N, 12C27, AEB-L & similar - all the way up to MagnaCut & CruWear. I'm doing some testing now to determine whether lower toughness steels can support a dual grit edge well including D2, 1% C ingot steels (VG10, 154CM etc.), as well as high carbide volume steels (Maxamet, 10V, 15V, K390, S90V, etc.); I should know something within the next year or so.

Cheers bro,

[The Home Slice]

Hey Gabe,
Welcome to the forum! I've enjoyed many of your videos; and, Thank You for taking the time and sharing.
I've oft wondered if your "dual grit edge" is the just the "fine side" being a good de-burrer of the coarse side burr, thereby getting closer to, or better achieving, a burr-free apex?
Based on the videos you and Pete have put the time into and shared, it (your dual-grit edge) seems to be a good edge. Thanks again for putting in so much time and sharing your data/findings.

u.w.

Thanks U.W. - much appreciated! I do think there is an element of combining of burr-formation/minimization tendencies going on.

When you abrade a large coarse-stone-burr with that same coarse stone, I think it causes too much violent bending and moving of metal for the edge apex to be very free from steel that has undergone permanent damage (plastic-deformation) these edges often remain too wide for a slicing to feel smooth, unless you do some very creative and thorough stropping.

When you thin out a burr with a fine stone, it often becomes too small to feel, but can still be present and is easily folded over or broken off, producing a wide or rounded surface which is less effective than desired.

It seems like if you use a fine stone (especially with a sort-of soft binder) in a dual grit edge, it realigns the coarse burr to center, removing some of the most damaged metal in the process and avoiding the first problem. It has been my experience that many dual grit stone combinations still require some amount of stropping to avoid the second problem.

That said, sharpening dual grit with no stropping at all has, in my experience, been a decent way to lessen the effects of both problems on a budget.

[Bill1170]

As soon as I read that this dual-grit edge is made with edge trailing strokes, my first thought was that this creates a serrated burr. Reading further that it works better with more ductile steels only reinforced that notion, because ductile steels burr more easily than super hard steels. Interesting work!