Insane performance boost in cutting ability!

About 5 or 6 years ago, I had a lot of thinning done by Tom Krein. Two of the knives were Spyderco Calypso Jr.s, one in VG10 and one in ZDP 189. I have to be careful with the VG10 and put a large microbevel on it, it was really too soft for this level of "thinness". The ZDP one was a monster, it held up well, probably due to it's higher hardness. I still put a fairly thick microbevel on it, and it cut like a light saber...
 
Thanks as well for the input and video Chiral! keep us posted...

sodak said:
About 5 or 6 years ago, I had a lot of thinning done by Tom Krein. Two of the knives were Spyderco Calypso Jr.s, one in VG10 and one in ZDP 189. I have to be careful with the VG10 and put a large microbevel on it, it was really too soft for this level of "thinness". The ZDP one was a monster, it held up well, probably due to it's higher hardness. I still put a fairly thick microbevel on it, and it cut like a light saber...
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Yeah it does need to be done with care and not just zero grinding everything for sure. But you are absolutely correct... it almost melts the atoms away as it cuts through stuff after a regrind! ;)
 
This should boost performance considerably... Emerson Journeyman that WAS a conventional primary grind with a belly, and had a chisel ground edge. I converted it to tanto v edge ~.005" 22-24 dps.

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I've been reading this thread and I think I'm starting to get it. "Thin is sharp." "It's not the angle, it's the thickness (at the shoulder?).

Now, I'm considering the "how." I don't want to do a full regrind. I want to do a relief bevel as someone mentioned with a targeted shoulder thickness.

My thought is I don't want to take material needlessly which is what I would do if I put in the relief bevel first all the way to the edge and then put in the primary edge. I'm looking that if I take the relief angle all the way to the edge, I'm just going to have to remove that edge away until I get the primary edge angle I want.

So I'm thinking I should "rough in" the primary bevel first using the coarse stone then put in the relief bevel until I get the right shoulder thickness. Refine the relief bevel then refine the primary edge. This would minimize the material removed while still getting both primary edge angle and shoulder thickness that I want.

Am I correct in my thinking?
 
Rey HRH said:
I've been reading this thread and I think I'm starting to get it. "Thin is sharp." "It's not the angle, it's the thickness (at the shoulder?).
Click to expand...

Exactly. Think of it this way. If you took a toothpick and a pencil, sharpened the end to the exact same angle and tried to poke them through the same t-shirt, which would go through easier?

Now, I'm considering the "how." I don't want to do a full regrind. I want to do a relief bevel as someone mentioned with a targeted shoulder thickness.

My thought is I don't want to take material needlessly which is what I would do if I put in the relief bevel first all the way to the edge and then put in the primary edge. I'm looking that if I take the relief angle all the way to the edge, I'm just going to have to remove that edge away until I get the primary edge angle I want.

So I'm thinking I should "rough in" the primary bevel first using the coarse stone then put in the relief bevel until I get the right shoulder thickness. Refine the relief bevel then refine the primary edge. This would minimize the material removed while still getting both primary edge angle and shoulder thickness that I want.

Am I correct in my thinking?
Click to expand...

Well let's go back to these terms:

Edge-Bevel.jpg


A quick note: a micro-bevel isn't pictured above but basically it would be the actual edge applied to the apex of the secondary bevel. It is almost invisible when you look at it.

What it sounds like to me that you are saying is that you want to lower the secondary bevel to a lower dps angle, then put in a micro bevel... is this correct?

sorry I am kind of confused w/ your terms...
 
Rey HRH said:
I've been reading this thread and I think I'm starting to get it. "Thin is sharp." "It's not the angle, it's the thickness (at the shoulder?).

Now, I'm considering the "how." I don't want to do a full regrind. I want to do a relief bevel as someone mentioned with a targeted shoulder thickness.

My thought is I don't want to take material needlessly which is what I would do if I put in the relief bevel first all the way to the edge and then put in the primary edge. I'm looking that if I take the relief angle all the way to the edge, I'm just going to have to remove that edge away until I get the primary edge angle I want.

So I'm thinking I should "rough in" the primary bevel first using the coarse stone then put in the relief bevel until I get the right shoulder thickness. Refine the relief bevel then refine the primary edge. This would minimize the material removed while still getting both primary edge angle and shoulder thickness that I want.

Am I correct in my thinking?
Click to expand...

Sharpness at the apex is a function of apex-diameter and everything behind it, i.e. thickness - the lower the apex-diameter, the sharper the edge; and the thinner the edge the deeper the penetration due to decreased 'wedging'.
Strength of the edge is a function of material support, i.e. thickness - the thicker the edge as measured however far back from the apex, the stronger the edge at the expense of penetration.
You always want a low apex-diameter, but varying the angle behind the apex produces a stronger or weaker edge based on how angle corresponds to the thickness of the material. You need a blade strong enough to handle the stresses of use but thin enough to not impede cutting performance.
Commonly the stresses of use only threaten the first millimeter or few of cutting edge, so this becomes your edge-bevel that must be resharpened as the blade dulls with use. Behind the edge, you transition into the strength of the blade itself that holds the edge in place, and once again the principles of thick vs thin apply. A thick shoulder indicates increased strength, a thin shoulder indicates increased cutting performance through less wedging. You want that shoulder as thin as possible without compromising the strength of the blade in the uses to which it will be subjected.

On terminology, most knives have only one edge, i.e. the cutting edge. It is not a "primary" edge, it's the only edge, produced by the meeting of bevels on either side of the blade.

Most makers grind the primary bevel down to a certain thickness at the edge before they ever add a sharpened edge via a secondary bevel. When the edge dulls, this edge-bevel is ground again. It sounds like you are describing the same thing. You only regrind the primary bevel if the blade is too thick behind the edge-bevel.
 
razor-edge-knives said:
What it sounds like to me that you are saying is that you want to lower the secondary bevel to a lower dps angle, then put in a micro bevel... is this correct?

sorry I am kind of confused w/ your terms...
Click to expand...

Not your problem with the confusion, I'm feeling my way around the terms so it's on me. And maybe I just don't have the proper sense of the resulting relative geometry of what I'm looking for, I haven't done the math yet.

Using your last diagram, flat ground profile. My vision is to put in a relief bevel which, as I understand it, is a bevel with an angle that is more than the primary bevel angle and less than the secondary bevel angle such that the thickness at the shoulder of the secondary bevel is "thin" enough.

(I don't know if throwing numbers will help or make it even more confusing. If the latter, then feel free to skip this part). Let's say the primary bevel is 5 degrees and the desired secondary bevel is 15 degrees. Then I want to put in a relief bevel at an angle somewhere between 5 and 15 degrees such that when I'm done, the thickness at the shoulder of the secondary bevel is .010" and it's still at 15 dps. I pulled these numbers from chiral.grolim's post on this thread stamped 02-02-2015, 04:05 PM.

And my previous post above was about how to get to this state with minimal material loss and modification of the knife dimensions assuming of course that what I want is directionally correct (i.e. obtuse enough angle at the secondary bevel to "hold" the edge and thin enough at the shoulder to be sharp.)
 
Rey HRH said:
Not your problem with the confusion, I'm feeling my way around the terms so it's on me. And maybe I just don't have the proper sense of the resulting relative geometry of what I'm looking for, I haven't done the math yet.

Using your last diagram, flat ground profile. My vision is to put in a relief bevel which, as I understand it, is a bevel with an angle that is more than the primary bevel angle and less than the secondary bevel angle such that the thickness at the shoulder of the secondary bevel is "thin" enough.

(I don't know if throwing numbers will help or make it even more confusing. If the latter, then feel free to skip this part). Let's say the primary bevel is 5 degrees and the desired secondary bevel is 15 degrees. Then I want to put in a relief bevel at an angle somewhere between 5 and 15 degrees such that when I'm done, the thickness at the shoulder of the secondary bevel is .010" and it's still at 15 dps. I pulled these numbers from chiral.grolim's post on this thread stamped 02-02-2015, 04:05 PM.

And my previous post above was about how to get to this state with minimal material loss and modification of the knife dimensions assuming of course that what I want is directionally correct (i.e. obtuse enough angle at the secondary bevel to "hold" the edge and thin enough at the shoulder to be sharp.)
Click to expand...

ahhh ok i see what you are saying now. yeah in order to have minimum steel loss you will probably want to alternate going from the relief to the secondary until you get it to where you want it.
 
I just want to thank the OP and everyone else who contributed to this thread.

It helped me reached an epiphany on sharpening and correctly juxtaposed the issues that were in the shadows of my mind but were still too ethereal for me to recognize. Now I have a frame of reference to put in context the stuff I've been taking in via threads on here, books and dvds I bought, and youtube videos.
 
I have reground a few knives of my own, but none for others. I reground my barong machete from Cold Steel to a primary bevel of about 4.5 degrees per side, then sharpened at various angles to suit use. That blade is currently a root cutter and dandelion digger, so the edge really hasn't been present for a while. It was a very nice cutter before that though.

I also reground a longer machete to the same bevel angle and gave it an edge angle of around 18-20 degrees per side. It's the only blade I've used that would cut an empty 2 liter bottle and leave the bottom sitting on the table. Too bad the regrind didn't fix the horrible handle.

I don't know why 15 dps/30 degree inclusive should be a hard and fast rule. I've seen edge angles recommended as low as 5 dps depending on use. If my work knife were only used for cutting, not scraping or other such lateral uses, it would have as thin an angle as I could manage. My trapper has a dedicated cutting blade at 7 dps with a 10 dps microbevel, and cuts copper wire and aluminum cans without damage. Now, the spey blade is 20 dps and gets used for all sorts of things. Most scandi/bushcraft blades are less than 30 degrees inclusive, and while some add a microbevel, many consider the notion silly, and are happy with the use they get. Spyderco makes knives with included edge angles of less than 20 degrees. My serrated Salt 1 was between 14 and 18 degrees inclusive, depending on which scallop was measured. I used it for cutting very rough material (rock wool sprayed on fire proofing) without damage other than dulling.

Lowering the thickness behind the edge increases cutting ability and lowering the edge angle increases edge holding, as long as it's still strong enough. This depends entirely on the user and the use. The most consistent sharpening angle advise I've seen is to sharpen at the lowest angle that resists damage. This can be expanded by adding the lowest edge thickness as well. The last knife I reground was my old Buck Scoutlite. I reground it to a zero edge, nearly completely removing the hollow grind. Then I sharpened it at various angles until I settled on a 12 dps back bevel with 15 dps microbevel. It now sports a 17 dps backbevel and 20 dps microbevel. The main reason for the change is the edge has thickened significantly, and it just takes less metal removal to resharpen. I'm slowly regrinding it again with a coarse stone, and at some point it will be thin enough to go back to the thinner angles.
 
chiral.grolim said:
I also recently came across GravityRoller's adjustments to a couple of Kershaw camp-knives - still a bit heavy behind the edge but a definite improvement:
Click to expand...

chiral.grolim,

Appreciate your comments here. I agree “still a bit heavy behind the edge”. But, both of these knives have continued down the road of thinning & testing since that video you linked. I’ll post links to a couple additional progress videos below. I hope it's not out of place to post here, but would appreciate any constructive comments or thoughts you and or the OP may have.

These two knives are/were part of a progressive sharpening project to see first-hand for myself the results of “thin” geometry, how improvements can be made, etc. Progressive, meaning (instead of taking an Eastern approach and starting very thin, then steepening if/when damage occurs), somewhat more Western approach of getting thin through first hand performance testing. I had a general idea of where I thought/hoped this project would end up, but rather than just assume I knew anything I chose instead to progressively go down the path to thinness while along the way progressively testing the edges back to back in real world usage testing (that included one trip to the ER for the owner of the Camp-10 … along with a hot ER Doctor :-) vid's below hopefully of Dr. Martens in action.

The only reason for the videos was self-documentation (a way of keeping us and the blades honest through this process of enlightenment, and to be able to review where we had come from without presumption of where we would end up). My “belt grinding” on these two leaves a lot to be desired, and once we actually pick the final grinds I intend to clean things up. I have been using an Edge Pro Apex to set a triple bevel at the secondary grind area as a control method for the final convex secondary geometry. Effectively, the edge bevels referenced are the angle closet to the edge-apex, then two progressive back-bevels that transition into the primary. The grinds are also asymmetric from ricasso to tip, and the Outcast is asymmetrical from left to right (flatter on left side in the right handed work area). My hat is off to you guys for the awesome grinds I have seen by others here in the forums, they look VERY Nice!

As referenced in the videos, I plan for the final grind to have a slight maintenance micro-bevel that will effectively give a bit of extra strength to the final geometry. The initial assumption/hope that I had planned on was 15-dps in the chopping area, and something less in the feather-sticking area (to allow the knives to be flatter to the stick allowing ease of pressure along the grain while cutting). I plan on one more full-day of testing these two in the field before deciding if progressing to shallower angles once again.

Here’s the video progression of these two knives from current condition back a few sharpening’s:
Hope these links are all working :-/

[video=youtube;5ehzPejtSe4]https://www.youtube.com/watch?v=5ehzPejtSe4&list=PLKO2m4TQ_9r4TtiI449zwgjD fYYKk1vtZ&index=6[/video]

[video=youtube;G-fn4-BbCSE]https://www.youtube.com/watch?v=G-fn4-BbCSE&list=PLKO2m4TQ_9r4TtiI449zwgjDfYYKk1vtZ&inde x=15[/video]

Video below Camp-10 has a single secondary bevel at 20-dps continuous ricasso to tip (this was the first regrind/rebevel on this knife).
There are specific notes on each grind in the notes section of each of these YouTube videos.

[video=youtube;BBQVbxfIeK8]https://www.youtube.com/watch?v=BBQVbxfIeK8&list=PLKO2m4TQ_9r4TtiI449zwgjD fYYKk1vtZ&index=12[/video]

Progression Cont Next Post (hopefully)
 
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Con't Camp-10 & Outcast

[video=youtube;s51GcAPaeHE]https://www.youtube.com/watch?v=s51GcAPaeHE&list=PLKO2m4TQ_9r4TtiI449zwgjD fYYKk1vtZ&index=14[/video]

[video=youtube;trBJ3ZWbbxw]https://www.youtube.com/watch?v=trBJ3ZWbbxw&list=PLKO2m4TQ_9r4TtiI449zwgjD fYYKk1vtZ&index=13[/video]
 
Con't Camp-10 & Outcast


And for the hot ER Doctor, Camp-10 owner and just 'cause we all like stitches & novacaine ... right ...?

[video=youtube;BwKa-67f2Cs]https://www.youtube.com/watch?v=BwKa-67f2Cs&list=PLKO2m4TQ_9r4TtiI449zwgjDfYYKk1vtZ&ind ex=16[/video]

[video=youtube;gKXvLXHkptA]https://www.youtube.com/watch?v=gKXvLXHkptA&list=PLKO2m4TQ_9r4TtiI449zwgjD fYYKk1vtZ&index=17[/video]
 
chiral.grolim,
Appreciate the comments on the Camp-10 & Outcast project I've been doing ;-)

RE: Secondary on a Scandi
I really do not understand this. It seems to go against the whole principle of Scandi grind in the first place. A Scandi typically has a primary bevel that is 2x to 3x dps (degrees per side) than knives designed to wear a secondary (typically 5-dps or less). If on the other hand a Scandi is very shallow at or below 10-dps, then I can understand a micro-bevel (provided the steel needs reinforcment behind the cutting edge), but a full secondary on top of a Scandi really seems ... (Let's just say I am stumped on the why one would choose to do this ...).

Edit:
I found the thread this image came from and it appears that I misinterpreted the picture. It appears that the Scandi grind at the cutting edge is still there and that a back bevel has been ground above that (what I would normally associate as the primary grind). So it appears now to be a flat ground blade with a secondary and probably relatively resultant thin spine. Maybe the project was to turn a Mora into a fillet knife (don't know, but still confusing to me).
 
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I've made a thousand knives; therefore I've ground two thousand bevels. In the making of a knife the first or primary bevels to be ground are those that originate at the spine. It's impossible to grind the cuttting edge before the first or primary bevel is ground. There should be no confusion about this. Its a matter of the order in which they are ground and, of course using an English dictionary.

I use the term back bevel to mean any grind thats done above the cutting edge and that does not reshape the primary or first bevel.

Good thread, Fred
 
Fred.Rowe said:
I've made a thousand knives; therefore I've ground two thousand bevels. In the making of a knife the first or primary bevels to be ground are those that originate at the spine. It's impossible to grind the cuttting edge before the first or primary bevel is ground. There should be no confusion about this. Its a matter of the order in which they are ground and, of course using an English dictionary.

I use the term back bevel to mean any grind thats done above the cutting edge and that does not reshape the primary or first bevel.

Good thread, Fred
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That's how I've always perceived it, with grinds named according to the order in which they're originally applied ('Primary' always means 'first', 'secondary' comes after that, etc). I'm not sure where or how I came to view it as such; might've read similar views from other knifemakers. But it's good to hear I wasn't confused. Simple and logical. :)

Thanks Fred. :thumbup:


David
 
Spey said:
Edit:
I found the thread this image came from and it appears that I misinterpreted the picture. It appears that the Scandi grind at the cutting edge is still there and that a back bevel has been ground above that (what I would normally associate as the primary grind). So it appears now to be a flat ground blade with a secondary and probably relatively resultant thin spine. Maybe the project was to turn a Mora into a fillet knife (don't know, but still confusing to me).
Click to expand...

It was originally confusing to me too :) But this picture I made seemed to really help me clarify in my mind what is going on:

Scandi.jpg


The bold red line is a typical scandi grind, which from reading i have done normally range from about 12-15 dps there on the edge. So my point is that if you could have a .030" thick edge w/ a conventional primary/secondary, why would you want to go thicker than that when .030" is plenty to resist pretty much any and all lateral deformation when chopping? going thicker, like on a scandi, seems counter productive.
 
razor-edge-knives said:
It was originally confusing to me too :) But this picture I made seemed to really help me clarify in my mind what is going on:

Scandi.jpg


The bold red line is a typical scandi grind, which from reading i have done normally range from about 12-15 dps there on the edge. So my point is that if you could have a .030" thick edge w/ a conventional primary/secondary, why would you want to go thicker than that when .030" is plenty to resist pretty much any and all lateral deformation when chopping? going thicker, like on a scandi, seems counter productive.
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Exactly. And this is why that scandi grind resists deformation/damage so well - it's a very thick grind. That's how you can get by with a softer steel. I would rather have the thin grind with a steel strong enough to support the edge. It will cut much, much better.
 
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