To add a secondary (or back) bevel or not to?

miso2

miso2

Joined
Nov 19, 2014
Messages
2,633
Hi all,

I had reprofiled my ZT 0770CF M390 from the factory angle of around 20 DPS to 15 DPS. So far, I love the improved cutting performance and better retention of the initial sharpness than before. But, this reprofiling made the edge bevel quite wide (see the pic below) and therefore the width-behind-the-edge thick. Since I have learnt in this forum and elsewhere that these things could affect cutting performance and ease of sharpening, I am wondering whether I should put back bevels to make the knife work better.

Should I add back bevels and which angle should I choose? And how wide the edge bevel should be after putting the back bevels?
I would appreciate your inputs.


IMG_0326.JPG
 
I would suggest,your knife your call.All my folders are sharpened at 20 DPS,I don’t bother with a back bevel I am happy with the cutting performance.
 
Knife looks great ;-)

How far up should you take a back-bevel ...?

Ideally, I would say all the way up to the flats & swedge before the spine. Basically a full reprofile of the primary (from secondary up). Anything less is a compromise.

One step in direction of compromise would be to take down the shoulder between the original primary & your new secondary bevels (perhaps somewhere half way between the two current bevels degrees).

What you decide is fairly personalized based on what you plan to use your knife for, and possibly your preference related to aesthetics.

Personally, I think super wide bevels on otherwise stone/acid-washed blades looks outta place. If the added potential performance is needed/wanted, well then ... form-follows-function over rules every time in my mind.
 
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Spey,

Thanks for the compliment. I used Edge Pro, and that is why it looks great (not my sharpening skill).

I did consider doing regrind but do not own equipment for it. I guess it can be done with sharpening stones, though I am not sure if I can do it properly without destroying the knife with my skills....... I will leave it as it is for now......


Miso
 
Unless it is hindering performance, I'd leave it as is. Would be fairly easy to thin it out by hand, but cosmetically finishing it off by hand takes a lot of time.
 
HeavyHanded,

Since I have never compared performance before and after putting back bevels, I don't know whether the wide bevels hinder the performance. I just thought that putting back bevels would boost the performance, when done properly. I am pleased to learn that regrind can be done freehand but not still sure whether I can do it myself. Thanks for the info.


Miso
 
Miso,

just want to point out that "bevel thickness" is often misunderstood. If you have a 20 dps that is .020" thick at the shoulder and then you reprofile that edge to 15 dps and it is .030" thick at the shoulders then the reprofiled will actually cut better than the "thinner" 20 dps edge. The reason being is because, when you reprofile, you are actually pushing the edge back into the thicker part of the blade but before you reprofiled, the thickness of the blade was still there, it just was thicker near the apex whereas now it is the same overall "blade thickness" further away from the apex.

Sorry if this is not making sense, it would be easier w/ visuals.

So if you do put a back-bevel on that one then note that your edge will be even wider, although it WILL cut better. And I do also agree that doing a full regrind of the primary would make it perform like you would not believe.
 
miso2 said:
Hi all,

I had reprofiled my ZT 0770CF M390 from the factory angle of around 20 DPS to 15 DPS. So far, I love the improved cutting performance and better retention of the initial sharpness than before. But, this reprofiling made the edge bevel quite wide (see the pic below) and therefore the width-behind-the-edge thick. Since I have learnt in this forum and elsewhere that these things could affect cutting performance and ease of sharpening, I am wondering whether I should put back bevels to make the knife work better.

Should I add back bevels and which angle should I choose? And how wide the edge bevel should be after putting the back bevels?
I would appreciate your inputs.


IMG_0326.JPG
Click to expand...

The width of the bevels only indicates what you've done, which is to reduce (thin) the edge grind angle on the relatively thick blade. That effort, by itself, has already improved cutting performance. Unless I'm misinterpreting what you're saying, the width 'behind the edge' is, in reality, no thicker than before; in fact, it's thinner at the same distance immediately behind the (old) edge bevels, as compared to what it was before you re-ground the edge. Adding a 'back bevel' would additionally thin the blade above the edge grind, which always improves cutting as well. But, there's no reason to worry about diminished cutting performance right now, based on the width of the cutting bevels alone.

Again, if I'm misinterpreting what you're trying to do/say, please disregard my point above. But it reads (to me) as if you're worried the wider bevels are indicating that the cutting geometry is thicker than before, which it isn't. Bottom line: as the cutting geometry (edge angle) gets thinner by grinding new bevels, the bevels resulting from that will get wider, as measured from the apex to the shoulder of the new bevels. The thicker the overall blade stock is, the wider those new bevels will appear. Again, that's not an indicator of poor (thick) edge geometry, but just the opposite.


David
 
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Obsessed with Edges said:
The width of the bevels only indicates what you've done, which is to reduce (thin) the edge grind angle on the relatively thick blade. That effort, by itself, has already improved cutting performance. Unless I'm misinterpreting what you're saying, the width 'behind the edge' is, in reality, no thicker than before; in fact, it's thinner at the same distance immediately behind the (old) edge bevels, as compared to what it was before you re-ground the edge. Adding a 'back bevel' would additionally thin the blade above the edge grind, which always improves cutting as well. But, there's no reason to worry about diminished cutting performance right now, based on the width of the cutting bevels alone.

Again, if I'm misinterpreting what you're trying to do/say, please disregard my point above. But it reads (to me) as if you're worried the wider bevels are indicating that the cutting geometry is thicker than before, which it isn't. Bottom line: as the cutting geometry (edge angle) gets thinner by grinding new bevels, the bevels resulting from that will get wider, as measured from the apex to the shoulder of the new bevels. The thicker the overall blade stock is, the wider those new bevels will appear. Again, that's not an indicator of poor (thick) edge geometry, but just the opposite.


David
Click to expand...

So much more elegantly said... Thanks David!
 
razor-edge-knives said:
So much more elegantly said... Thanks David!
Click to expand...

After I posted, I saw your explanation, and was equally impressed about your perspective on it. Looks like we're reaching the same conclusion; I was worried I might be misreading what's being described in the OP, but maybe not.

Thanks Josh. :thumbup:


David
 
Josh,

It does make perfect sense to me. I remember your post of regrinding and wowed by the reground knife. I wish I could do it on my knives like that!

Since I am happy with the performance and the look of 0770cf as is, I will leave it. But I will try to regrind my Manix S110V with water stones to see the performance boost myself.

Thank you for the info,


Miso
 
David,

Thank you for the info. Together with Josh's explanation, it is now clear to me. I was confused with the definition and the interpretation of the "bevel thickness".


Miso
 
miso2 said:
Josh,

It does make perfect sense to me. I remember your post of regrinding and wowed by the reground knife. I wish I could do it on my knives like that!

Since I am happy with the performance and the look of 0770cf as is, I will leave it. But I will try to regrind my Manix S110V with water stones to see the performance boost myself.

Thank you for the info,


Miso
Click to expand...

You will want to use silicon carbide at least and finish with diamonds on that steel, preferably diamond plates for the entire job if doing by hand. I'm no expert on s110v, but while your waterstones may well sharpen it acceptably, removing larger amounts of steel from the primary grind will be painfully slow going.
 
HeavyHanded,

Thanks for the tips. I've got some hard silicon carbide stones for EdgePro and will try to use it for regrind. If it is too hard and slow, I will get diamond plates.


Miso
 
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