Dual bevel, or no?

S

SixTwelve

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Jan 14, 2016
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My question is about the cutting edge. Regardless of the type of grind, does anybody put a different angle on the actual cutting edge, and if so, why? I am confused about this. I have made a few knives, and to this point I have just allowed the angle of the bevel to continue to the edge. I try to hit somewhere between 18 and 22 degrees, and it has worked out great. From what I see, to produce a dual bevel it would be necessary to make the secondary bevel at a larger angle than the primary. I can't understand the functional reason for this.
Someone please explain.

Thanks
 
I am a little confused by the question. Are you doing a scandi grind? If so, most of those don't have a secondary bevel. If its a full flat grind the bevels will be around 2-5 degrees or so and will have an edge bevel of 10-20 degrees per side.
 
I think he's saying he goes to a zero edge grind. so the edge would be 2-5 degrees on a FFG. I put on about 18degree edges on my FFGs
 
Both methods are viable, though most makers typically prefer a secondary bevel so that the edge isn't as fragile. The angle will usually depend on the intended role of the knife.
 
Scandi grinds are normally 12 or 12.5 dPS or 24--25 inclusive. In their original form there was no second grind at the edge.

Bowie knives with full flat grinds, ones that are 2" +high will accept an angle of 2 or 2 1/2 degrees per side when grinding the primary bevels. If taken to a zero edge, this angle will not support a strong cutting edge, One that measures 4 or 5 degrees inclusive is far to weak to hold up to any cutting chore. Straight razors are in the 12 to 14 inclusive range. The change in angle is selected, with most makers deciding which angle by observing the edge thickness and thickness of the spine. A blade that is ground to a zero edge can carry a more obtuse angle at the edge, {it's thinner} With thicker edges it makes more sense to use a more acute angle { the edge at the shoulders is thicker } and therefor will not cut as well, a steeper edge angle is needed for it to perform well.


Choosing an edge angle should begin when the knife is designed; in this way you will edge up with a blade geometry that is proportional and functional.

Finely made kitchen slicers will be ground to a fine zero edge and any angle that is used to sharpen the blade will not be noticeable.

Its all about the geometry, Fred
 
Fred,
I see those numbers for a Scandi regularly, but they don't work. In 1/8" stock, a 25 degree edge would only go up a tad less than .3"

What I have seen in most older Scandi grinds is a basic primary bevel that was forges in the blade, and the zero edge bevel ground on the sharpening stones going up about 1/2". So, in fact, they do have a dual bevel.
 
Stacy E. Apelt - Bladesmith said:
Fred,
I see those numbers for a Scandi regularly, but they don't work. In 1/8" stock, a 25 degree edge would only go up a tad less than .3"

What I have seen in most older Scandi grinds is a basic primary bevel that was forges in the blade, and the zero edge bevel ground on the sharpening stones going up about 1/2". So, in fact, they do have a dual bevel.
Click to expand...

My experience is only with thicker stock and I am confident you are correct with your post. Using an ERU I have found them to be anywhere from 12 incl. to 15 inclusive. It never ceases to amaze me the geometries that can be found in knives.

Hope your year is going well, Fred
 
knife to a gunfight said:
Both methods are viable, though most makers typically prefer a secondary bevel so that the edge isn't as fragile. The angle will usually depend on the intended role of the knife.
Click to expand...

This. Thinner cuts better is the general rule. So you want your edge angle as low as possible, your edge/grind thickness to be as thin as possible, and your grind height and stock thickness to be as thin as you can get WITHOUT compromising strength or toughness for the intended purposes. You don't want to compromise any part of the geometry by going too thin but you don't want to be overly thick either. This is where testing and experience on the part of the knife maker comes in to play.

The purpose of a back bevel/relief bevel/secondary is to thin out the cutting edge a little thinner than you normally would be able to go, then you can apply a final bevel (micro or close to it) at the normal geometry.

This is one of the best ways I have seen to fine tune your knives.

[video=youtube;Hy23qeCL1s8]https://www.youtube.com/watch?v=Hy23qeCL1s8[/video]
 
Fred.Rowe said:
My experience is only with thicker stock and I am confident you are correct with your post. Using an ERU I have found them to be anywhere from 12 incl. to 15 inclusive. It never ceases to amaze me the geometries that can be found in knives.

Hope your year is going well, Fred
Click to expand...

Actually, the thinner the stock, the less the bevel would go up the side on a scandi. In 1/16" stock, a 25° grind line would be about .15" high.
 
Ok fellas, wow you lost me there but that's ok. Apparently I need to get some better prerequisite knowledge before I will understand this topic fully, but for now it's enough to know that my current thinking is flawed. My trig is pretty good so I should be able to figure this out. I will watch the suggested video from Josh and if I have more questions maybe I can voice them in a more intelligent manner.

Thanks to everyone that replied!!

Will
 
SixTwelve said:
My question is about the cutting edge. Regardless of the type of grind, does anybody put a different angle on the actual cutting edge, and if so, why? I am confused about this. I have made a few knives, and to this point I have just allowed the angle of the bevel to continue to the edge. I try to hit somewhere between 18 and 22 degrees, and it has worked out great. From what I see, to produce a dual bevel it would be necessary to make the secondary bevel at a larger angle than the primary. I can't understand the functional reason for this.
Someone please explain. Thanks
Click to expand...

I'll start with some terminology:

INCLUSIVE: Explained in this image http://kitchenknifeguru.com/wp-content/uploads/2012/03/included-angle2.png It is used to avoid ambiguity when describing angles.

EDGE THICKNESS: Illustrated in this image http://kosterknives.com/ScandiVsFlat.gif - in the 'Flat' grind, the edge thickness is 0.013". It is often described as the 'thickness behind the edge' or 'the thickness of the edge before sharpening.'

ZERO EDGE: Describes a knife with no secondary bevel - i.e. what you are doing, as far as I can tell.

SCANDI GRIND: A somewhat ambiguous term that means different things to different people. Most agree that it is a steeper primary bevel, usually with a zero edge. Again, it sounds like you are doing a scandi grind. A scandi grind can be thought of as a saber grind (google it) with a zero edge.

FLAT GRIND: Another somewhat ambiguous term. Most agree it is a shallower primary bevel, always with a secondary bevel.

Anyway, hopefully with that terminology defined, you can make sense of the replies in this thread and here http://www.bladeforums.com/forums/showthread.php/1068324-Which-is-better-for-batoning-Scandi-or-Flat
 
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