Insane performance boost in cutting ability!

[REK Knives]

So I wanted to do a thread to clear up some confusion that I think has taken place in different areas of the knife world, especially among those new to knives. 4-5 years ago when i got into knives I had no idea what a "regrind" was. Even after really getting heavily into sharpening I was unfamiliar with a regrind and how much of a difference it makes in cutting ability.

So I wanted to do a thread to add some clarity to the issue and to point out that a regrind is not for everyone, but it may be for you - read below.

What is a regrind?

So what is a regrind? Hopefully this can help you out:

[video=youtube;i54jtT9Onuk]http://www.youtube.com/watch?v=i54jtT9Onuk[/video]

Keep in mind that this term can be used also when it comes to your actual edge, such as " I need my edge reground" but really what you mean is "I need my edge reprofiled." So a couple of terms need to be defined:

Primary grind
Secondary grind
Micro-bevel

There is definitely some confusion regarding these terms, and as best as I can tell it comes from the difference between the terms on Japanese type knives and Western type knives. In this first picture below, you will see the terms as used with typical japanese knives. These are the terms that Murray Carter uses:

In this other picture below, these are the terms that I tend to favor more, for a couple of reasons. 1. it makes more sense to me, as the primary grind is the main grind that makes a blade blank into an actual knife. 2. if you have a zero ground blade, using the first picture that would have to be called the 'secondary edge/bevel', which is can be confusing.

And when you get into micro bevels, they are "micro" as in you can either barely see it or not at all. this should be done at higher angles than the edge had been finished at with very light passes. this add's strength to the edge to resist lateral deformation and can also make sharpening much easier. But keep in mind that as you sharpen a micro bevel, it can turn into a "secondary bevel".

Is a regrind right for me?

Well, it depends... what are you wanting to use the knife for? Back to the OP thread title... thinning the entire primary grind down does give you a DRASTIC performance increase, the likes of which most people have not experienced unless they have gotten into customs. It will go longer before *feeling* dull and is MUCH easier to sharpen.

The down side to a regrind is that it *can* make the tip relatively weaker (the extent depends on your blade geometry) and *can* make the edge less resistant to lateral deformation or even blow outs depending on many factors (such as stock blade thickness, grind height and type, and how thin you go w/ the regrind). Although this isn't always the case. This is why a regrind must be customized to the knife and the need of the individual. Personally, I love a dual grind, where you have a spanto or tanto type grind in which the main edge is thinner and the tip left thicker for prying. But basically, if you are not planning on using this for batonning or prying then a regrind would be your optimal choice! If you are, then it still may be desirable in such cases as this, where it is optimized for the specific tasks at hand. Many times the blade is far too thick from the factory.

So if you want high slicing ability and super cutting performance, then yes, you won't experience anything better... this is the "next level" to sharpness. But if you want to use your knife as a pry bar or chopper, then I would suggest customizing your primary and secondary grinds for the hardest task that will be demanded of it (Please click here for an example of a custom grind) . From what I have read and experienced a .030-.035" thick edge is optimum for chopping whereas for slicing, an edge <.010" thick will be optimum.

Another point I want to make about what may be right for you is on zero grinds. A zero grind is basically where you have no secondary grind but the primary grind tapers all the way down and IS the edge. This is the case on things like scandi bushcraft knives. And you have probably heard about "zero ground" Emersons (only ones that come from the factory this way are their customs). Emersons do so well being zero ground because they have such a low primary grind height the edge is still pretty strong.

Lastly, if you want an edge that can retain a lot of strength but still increase cutting performance somewhat, your best bet is a compromise. What do I mean? It is something called a "back-bevel" which basically allows you to thin your edge out (by lowering your edge angle somewhat, maybe to 10-15 dps) and then you can micro bevel that edge for strength. While not as good as a regrind, this is a great option for people who have a Spyderco Sharpmaker for instance, as you only have to re-profile once and then you can maintain at the 20 dps setting, or if you simply want an enhanced performance boost without all the hassle of a regrind . I will warn you though, regrinds are addicting!

Here are some pics of regrind work for more ideas on what I have mentioned above.

How do I regrind my knives?

Well you can get a coarse grit stone, lay it to where the primary grind is flat on the stone, and grind away giving care to put more pressure towards the edge. Or you can use a belt grinder (which is much faster). However with power grinding extreme care must be given so as to not over heat the edge, especially when zero grinding. This is one reason why I use and suggest others use, a liquid cooling system if possible. The first method is mainly for function. It will function just fine, just not necessarily be "pretty". The second can look nice if you go slow and take your time, and have some experience under your belt. Any knife maker on these forums pretty much can do this as this is how primary grinds are "roughed in" to blade blanks.

If you choose to do this, please post up feedback as I would love to hear how it went and feedback on use.

Please post up pics if you have them!

In these pics below (before and after) notice the thick edge before and the after (a consistent ~.010" thick edge).

 

[chiral.grolim]

Can we just leave out the Murray Carter nonsense that isn't English?? In English, an "edge" is only formed when two planes meet, and the only edge we care about in knives is the cutting edge. The only way to have a "secondary edge" is between two planes meeting at some secondary location. I guess that you could call the tip-region of a Western Tanto the "secondary edge" to separate it form the "primary edge" along the belly. But in those images from Carter, the "secondary edge" doesn't exist, it indicates a plane not the meeting of planes, it's not English. If we're going to use Japanese terminology we need to use the actual japanese terminology which was apparently mistranslated for that diagram.


EDIT to add:

you also might mention that you can add a "relief" or "back" bevel between the edge and primary bevels by simply grinding at an angle between the other two, very simple to do on a hollow-grind primary, thereby thinning behind the edge without needing to remove much material or excessively impacting blade strength. Here is my adjustment of a Muela PIK-AS skinning knife down from 0.035" to 0.010" behind the 15-dps edge bevel:

 

[REK Knives]

Done, and thanks for pointing that out Chiral!

 

[Rey HRH]

Thanks for your contribution, OP.

And I suppose that between leaving the primary bevel as is and regrounding to the fullest as in your example, there is an acceptable medium of reprofiling the knife to have the primary bevel less than the factory but more than the most acute angle possible?

For example, if the factory edge is 20 degrees and the most acute angle possible is 5 degrees to hit the thickest part of the blade, 10 degrees is a possible compromise between slicing ability and lateral deformation resistance, yes?

 

[HeavyHanded]

I'm not entirely comfortable with the word "nonsense" being used in the same sentence as Murray Carter...

It makes more sense to me to describe what I call the "back bevel" as a secondary edge, than to call it the primary edge. The two planes would meet at a hypothetical edge (in fact on some handmade knives or ones ground from blanks, that meeting point may not initially have even been theoretical), if not for the primary edge being ground into that space. It is the edge that leads into the cutting edge - at least on knives with clearly defined planes.

My rule of thumb for thinning the back bevel is that 98% of all knives will benefit from and well tolerate it. Is no exaggeration to call it an insane boost in cutting perfomance.

Historical examples of utility knives generally are all quite thin stock. The overbuilt knife seems to have come into vogue as knife work diminished in daily use for most people so they lost the ability to assess tool geometry, and as a cosmetic selling point.

When in doubt, thin it out!

 

[chiral.grolim]

I'm not entirely comfortable with the word "nonsense" being used in the same sentence as Murray Carter...

It makes more sense to me to describe what I call the "back bevel" as a secondary edge, than to call it the primary edge. The two planes would meet at a hypothetical edge (in fact on some handmade knives or ones ground from blanks, that meeting point may not initially have even been theoretical), if not for the primary edge being ground into that space. It is the edge that leads into the cutting edge - at least on knives with clearly defined planes.

A man can be honorable in every other way and still have a poor grasp of English. That's OK, just don't perpetuate it.
The "primary edge" is the edge, i.e. where bevels meet to form one. There is NO "secondary edge" behind this edge or in front of it, it doesn't exist. That's nonsense. Furthermore a "hypothetical edge" does NOT describe a "bevel", and even if you tried to explain it that way, such an edge would be "primary" as it leads and is made before a relief/secondary bevel is ground. I described adding another bevel behind the edge as "back" but it could be given another term, so long as you don't call it an "edge" and I refer to it as the "back" bevel because it is ground after the edge-bevel and it certainly isn't "primary" as it wasn't ground first, has almost no impact on the geometry of the blade, and doesn't lead (least important). To call the actual primary-grind a "back bevel" implies that it isn't as important when it is actually MOST important to the overall geometry of the tool. The geometry of the edge can be changed easily and does change naturally as it gets dull and needs to be resharpened, but to alter the overall cutting geometry of the blade, you must alter the "primary grind" as the OP indicates. It's not a "back bevel". As you noted, on older knives you couldn't even SEE the edge-bevel and Scandi-blades try to avoid them altogether. To call it a "back bevel" would imply that Scandi-blades have ONLY a "back bevel" (since we all know that the very act of cutting rubs/grinds down the very edge).
There ARE actual Japanese terms for the anatomy of a knife blade and none of them refer to "hypothetical edge" or "secondary edge", those are a misuse of terminology. If you're going to use Japanese terms, use "Ha" for the cutting edge, use "Hira" or "Kiriba" for the bevel (not sure which is accurate), or better yet use the actual Japanese script, don't misuse English to try to explain...


I know, I need to relax.

 

[bgentry]

Thanks for the thread. Blade thinness is definitely misunderstood, or at least it's not widely understood. "Thin is sharp." Duh. But it took me many years to get that, even after being told by an old man I met. Anyway...

As to this whole debate about the terminology: I don't think primary or secondary properly describe the geometry of the faces of a typical blade. Inserting the word "edge" doesn't make sense either. We are talking about the shape of the sides of the blade, which we tend to call "bevels". The bevel that meets the cutting edge could easily be called primary, secondary, tertiary, micro, etc. So I just call that last bevel that ends at the edge, "the cutting bevel". It meets the edge and that's where the cutting takes place.

I'm easily hung up on terminology and using the right words. It makes me mildly irritated to hear people call the magazine in a pistol a "clip". It's not a clip; it's a magazine. This is well documented and understood by those in the know.

But in this case, I don't think there are any proper, well distributed, well understood terms for the exact parts of the sides of a blade. <shrug>

At least we mostly know what each other are referring to around here.

Brian.

 

[HeavyHanded]

A man can be honorable in every other way and still have a poor grasp of English. That's OK, just don't perpetuate it.
The "primary edge" is the edge, i.e. where bevels meet to form one. There is NO "secondary edge" behind this edge or in front of it, it doesn't exist. That's nonsense. Furthermore a "hypothetical edge" does NOT describe a "bevel", and even if you tried to explain it that way, such an edge would be "primary" as it leads and is made before a relief/secondary bevel is ground. I described adding another bevel behind the edge as "back" but it could be given another term, so long as you don't call it an "edge" and I refer to it as the "back" bevel because it is ground after the edge-bevel and it certainly isn't "primary" as it wasn't ground first, has almost no impact on the geometry of the blade, and doesn't lead (least important). To call the actual primary-grind a "back bevel" implies that it isn't as important when it is actually MOST important to the overall geometry of the tool. The geometry of the edge can be changed easily and does change naturally as it gets dull and needs to be resharpened, but to alter the overall cutting geometry of the blade, you must alter the "primary grind" as the OP indicates. It's not a "back bevel". As you noted, on older knives you couldn't even SEE the edge-bevel and Scandi-blades try to avoid them altogether. To call it a "back bevel" would imply that Scandi-blades have ONLY a "back bevel" (since we all know that the very act of cutting rubs/grinds down the very edge).
There ARE actual Japanese terms for the anatomy of a knife blade and none of them refer to "hypothetical edge" or "secondary edge", those are a misuse of terminology. If you're going to use Japanese terms, use "Ha" for the cutting edge, use "Hira" or "Kiriba" for the bevel (not sure which is accurate), or better yet use the actual Japanese script, don't misuse English to try to explain...


I know, I need to relax.

Calling it the back bevel in no way diminishes its importance. All the parts of the edge act in concert, all are important to the function of the tool.

And no, the Scandi and by extension the full convex and FFG are not made up of just a back bevel. The FFG and (true flat) Scandi can be simply described as a cutting edge - no primary, no secondary, no back bevel, no bevels at all till you get to the shoulder and flat on a Scandi, and technically there is still only one bevel as the flats are not a bevel. To call it a secondary anything is a misnomer.

I began using the term "back bevel" relative to convex edges, as there really is no terminology for different regions of a full convex, despite differences in geometry from one to the next. Nevermind there really are no bevels on an arc...

We also tend to work sides of the edge - just looking at the tool's surface we see one or several bevels that we influence by grinding. The final, or cutting bevel, meets to form an edge with the opposite side, all other bevels are "back" from this bevel.

A last thought, what is the point of calling it a "Primary Edge" in the first place, doing so implies other edges that are not primary. The Japanese do not have the final say on edge terminology, and apparently neither do any of us. As long as we all know what we're talking about it makes no difference whatsoever. I prefer "back bevel" and "cutting edge" or "cutting bevel". If that isn't understandable maybe we should all default to Japanese, but we're going to need a good Sticky...

 

[FTR-14c]

[QUOTE


I tend to use this method often and find it easy, low risk and it makes a world of difference in cutting performance.


you also might mention that you can add a "relief" or "back" bevel between the edge and primary bevels by simply grinding at an angle between the other two, very simple to do on a hollow-grind primary, thereby thinning behind the edge without needing to remove much material or excessively impacting blade strength. Here is my adjustment of a Muela PIK-AS skinning knife down from 0.035" to 0.010" behind the 15-dps edge bevel:

[/QUOTE]


Question for the OP:
Do use a jig when you do a regrind? Your lines look great.

 

[David Martin]

I have struggled to understand these made up terms as well. Once you go making up terms we need a definer to accompany them. So, everyone can get on the same page. DM

 

[Spey]

I "think" that if we are going to agree to use English ..., that the term "Primary" grind should mean the main or initial grind (unlike the Murray Carter English adopted terminology ...). And yes, I do understand Murray calls the first grind applied on a blade the "Secondary", and the second grind applied to a blade the " Primary". I have assumed it tradition he has picked up from Japan, that the "Primary" relates to the Primary-edge which by default has associated bevels ... But to me it is nonsensical to attempt translational tradition when we are Westerners speaking English (no disrespect Murray).

So,
Primary = first and/or main bevel or grind.
And, therefore
By default then the "Secondary" grind would be the next main bevel. Typically on most flat grinds (i.e. non concave or ogive grinds), this "Secondary" grind would reach the apex of the edge of the blade.

From here it seems pretty easy to understand a micro-bevel to the edge apex, back-bevel(s), shoulder(s) between bevels, etc.

Please, let's only have one "Apex" in our descriptive terminology, and let it be at the cutting edge regardless how many bevels there may be, and whether we are discussing flat or non-flat grinds that get us from spine to Apex, Ricasso to Tip.

To the OP - I think there is a lot of confusion in the potential interpretations that can be made from your original post. Example: you make a reference that a "regrind" means regrinding the primary bevel to thin the thickness of the blade at the transition between Primary & Secondary. I would argue that same term "Regrind" many times also relates to changing a Secondary bevel angle (like from 20-dps to 15-dps or less), or relocation the Ricasso effectively increasing the cutting edge length, etc. Regrind in my mind means "changing" any of the original grinds (Primary, Secondary, etc. or going from Convex to Flat, or Hollow to Flat, or visa-versa). I believe if you're going to use "Regrind", it should be accompanied with the associated bevel(s) that are being refereed (Primary-Regrind, Secondary-Regrind, etc.). Also, that the term Regrind may also be substituted with Reprofile by many folks.

When referring to Convex or Ogive grinds, I believe there should also be accompanying description like Convex-Secondary, full-Convex, etc. and the Ogive radius near the edge-apex (fat, lean, etc). I get a lot of owner convexed knives that to the untrained eye "look" beautiful, but perform horridly because they are what I'd term too fat (elliptical Ogive - like 9mm ball ammo vs spitzer bullet).

It seems many folks use, then reuse terms and phrases they have heard without either thinking or understanding what they are describing, how many meanings they could have without appropriate qualifier term. I'm gonna stop now.

Regards,

 

[REK Knives]

Thanks for your contribution, OP.

And I suppose that between leaving the primary bevel as is and regrounding to the fullest as in your example, there is an acceptable medium of reprofiling the knife to have the primary bevel less than the factory but more than the most acute angle possible?

For example, if the factory edge is 20 degrees and the most acute angle possible is 5 degrees to hit the thickest part of the blade, 10 degrees is a possible compromise between slicing ability and lateral deformation resistance, yes?

Yes all that needs to be taken into account for a regrind. When the primary is (using your example) 5 dps, I would regrind it to thin the entire primary grind out and then you can apply a secondary grind for edge strength and a micro bevel if desired. Maybe this thread can help you understand a bit more.

Calling it the back bevel in no way diminishes its importance. All the parts of the edge act in concert, all are important to the function of the tool.

And no, the Scandi and by extension the full convex and FFG are not made up of just a back bevel. The FFG and (true flat) Scandi can be simply described as a cutting edge - no primary, no secondary, no back bevel, no bevels at all till you get to the shoulder and flat on a Scandi, and technically there is still only one bevel as the flats are not a bevel. To call it a secondary anything is a misnomer.

I began using the term "back bevel" relative to convex edges, as there really is no terminology for different regions of a full convex, despite differences in geometry from one to the next. Nevermind there really are no bevels on an arc...

We also tend to work sides of the edge - just looking at the tool's surface we see one or several bevels that we influence by grinding. The final, or cutting bevel, meets to form an edge with the opposite side, all other bevels are "back" from this bevel.

A last thought, what is the point of calling it a "Primary Edge" in the first place, doing so implies other edges that are not primary. The Japanese do not have the final say on edge terminology, and apparently neither do any of us. As long as we all know what we're talking about it makes no difference whatsoever. I prefer "back bevel" and "cutting edge" or "cutting bevel". If that isn't understandable maybe we should all default to Japanese, but we're going to need a good Sticky...

Lol. I would agree that the "primary edge" would be the apex, or part of the blade that first makes contact with whatever you are cutting. But that is why I choose to refer to it as "primary grind" and "secondary grind", either of which could be done in such a way to form an apex.

[QUOTE


I tend to use this method often and find it easy, low risk and it makes a world of difference in cutting performance.


you also might mention that you can add a "relief" or "back" bevel between the edge and primary bevels by simply grinding at an angle between the other two, very simple to do on a hollow-grind primary, thereby thinning behind the edge without needing to remove much material or excessively impacting blade strength. Here is my adjustment of a Muela PIK-AS skinning knife down from 0.035" to 0.010" behind the 15-dps edge bevel:

Question for the OP:
Do use a jig when you do a regrind? Your lines look great.[/QUOTE]

I did not do the grinds you quoted/pictured, Chiral did. Mine are in the OP and no I don't use any type of jig and I do not believe that most other knife makers do either =)

I "think" that if we are going to agree to use English ..., that the term "Primary" grind should mean the main or initial grind (unlike the Murray Carter English adopted terminology ...). And yes, I do understand Murray calls the first grind applied on a blade the "Secondary", and the second grind applied to a blade the " Primary". I have assumed it tradition he has picked up from Japan, that the "Primary" relates to the Primary-edge which by default has associated bevels ... But to me it is nonsensical to attempt translational tradition when we are Westerners speaking English (no disrespect Murray).

So,
Primary = first and/or main bevel or grind.
And, therefore
By default then the "Secondary" grind would be the next main bevel. Typically on most flat grinds (i.e. non concave or ogive grinds), this "Secondary" grind would reach the apex of the edge of the blade.

From here it seems pretty easy to understand a micro-bevel to the edge apex, back-bevel(s), shoulder(s) between bevels, etc.

Please, let's only have one "Apex" in our descriptive terminology, and let it be at the cutting edge regardless how many bevels there may be, and whether we are discussing flat or non-flat grinds that get us from spine to Apex, Ricasso to Tip.

To the OP - I think there is a lot of confusion in the potential interpretations that can be made from your original post. Example: you make a reference that a "regrind" means regrinding the primary bevel to thin the thickness of the blade at the transition between Primary & Secondary. I would argue that same term "Regrind" many times also relates to changing a Secondary bevel angle (like from 20-dps to 15-dps or less), or relocation the Ricasso effectively increasing the cutting edge length, etc. Regrind in my mind means "changing" any of the original grinds (Primary, Secondary, etc. or going from Convex to Flat, or Hollow to Flat, or visa-versa). I believe if you're going to use "Regrind", it should be accompanied with the associated bevel(s) that are being refereed (Primary-Regrind, Secondary-Regrind, etc.). Also, that the term Regrind may also be substituted with Reprofile by many folks.

When referring to Convex or Ogive grinds, I believe there should also be accompanying description like Convex-Secondary, full-Convex, etc. and the Ogive radius near the edge-apex (fat, lean, etc). I get a lot of owner convexed knives that to the untrained eye "look" beautiful, but perform horridly because they are what I'd term too fat (elliptical Ogive - like 9mm ball ammo vs spitzer bullet).

It seems many folks use, then reuse terms and phrases they have heard without either thinking or understanding what they are describing, how many meanings they could have without appropriate qualifier term. I'm gonna stop now.

Regards,

Good points here, and I tend to agree with most of what you wrote. You did a good job explaining yourself. It would be nice to have a general consensus on the American terms that are used for sure. I have simply chosen (as others have) to have the term "regrind" refer to re-surfacing the entire primary grind, and "reprofile" refer to everything else that needs an angle lowered.

In the truest definition of the word, yes, regrind can be applied to any part of the blade that you are grinding away (i.e. regrind the tip, regrind the the bolster, regrind the secondary, etc). I am more of using the term "regrind' in a general/usual way but I do understand that it can be applied elsewhere. All i am saying is that when it is, then it should be specified whereas the default should mean "regrind the primary" as it has come to be understood in the knife world from my take on it.

I just wanted to point out that people DO have different definitions so when we talk about it things need to be specified. =)

 

[hiwa]

In the op's original post , the first diagram (parts of a blade) shows the edge as the "primary" edge and closer to the spine as the secondary "edge". Then the second diagram (flat/hollow grind) shows the edge as the secondary bevel and above it closer to the spine the primary bevel. Huh ? I know for sure I'm not the only one confused by this as I've seen it mixed up many times.

I've given up trying to decide on a name for things as there's constant contradiction. I just refer to the grind of the knife and what kind of edge it has and none of this primary/secondary nonsense. I've seen it flip-flopped too many times.

 

[G. Scott H.]

This is the terminology I've always used, though I sometimes also refer to the primary bevel as the primary "grind." As an example, I'd describe my Cold Steel Rajah II below as having a full flat primary grind with a secondary bevel. Carter is the only person I can think of offhand who refers to grinds and bevels the way he does.

 

[FTR-14c]

I did not do the grinds you quoted/pictured, Chiral did. Mine are in the OP and no I don't use any type of jig and I do not believe that most other knife makers do either =)

Copy that, I was referring to your OP. That is amazing.

 

[chiral.grolim]

Copy that, I was referring to your OP. That is amazing.

I second this ^ :thumbup: Well done.

 

[REK Knives]

I did not do the grinds you quoted/pictured, Chiral did. Mine are in the OP and no I don't use any type of jig and I do not believe that most other knife makers do either =)

Copy that, I was referring to your OP. That is amazing.[/QUOTE]

I second this ^ :thumbup: Well done.

Thanks guys.

And I agree with you Chiral on the terminology, it makes sense to me to refer to it as the Primary bevel or primary grind. =)

 

[sodak]

Can we just leave out the Murray Carter nonsense that isn't English??

Enough with the "nonsense" nonsense. Just because you want a term to mean a certain thing does not make it so. Everyone can use the terminology they like, as long as it makes sense, no harm is done. We are all free to use whatever terminology we prefer.

Razor Edge, you might want to do some searches on regrinds from about 4 or 5 years ago, when Gunmike1 (and others) were having Tom Krein do the grinds. We saw some pretty incredible increases in cutting ability.

 

[Rey HRH]

Razor Edge, you might want to do some searches on regrinds from about 4 or 5 years ago, when Gunmike1 (and others) were having Tom Krein do the grinds. We saw some pretty incredible increases in cutting ability.

I'm just asking: would those searches result in material that substantially add or differ from what the OP posted?

 

[REK Knives]

Enough with the "nonsense" nonsense. Just because you want a term to mean a certain thing does not make it so. Everyone can use the terminology they like, as long as it makes sense, no harm is done. We are all free to use whatever terminology we prefer.

Razor Edge, you might want to do some searches on regrinds from about 4 or 5 years ago, when Gunmike1 (and others) were having Tom Krein do the grinds. We saw some pretty incredible increases in cutting ability.

Yeah I'm quite familiar with krein regrinds I just wanted to post this thread to let some of the newer guys know what a regrind was as I have seen some confusion as of late