Why secondary and micro bevels?

[BMK]

Thank you. The secondary bevels that many of you refer to is a "micro Scandi" (if you will). What you are describing is a blade that has a Scandi working edge and that working edge does 100% of the cutting. In the end, it is a secondary convex bevel or a secondary Scandi bevel that is actually doing all the cutting. BTW, I think many axes that are used to chop wood are convex beveled.

The question remains, why not just use a single bevel to zero?

Anyone???

try to chop thru a log with a scandi ground knife let me know when you get there LOL....as was stated in a earlier post the "scandi" grind is for ease of sharpening IE there is no skill involved in sharpening one of these blades ....lay it on the stone and drag it back and forth that's why its so popular go to a "survival" skills class and that's what they teach....as to your original question why the secondary edge bevel because that's the way its done. i really dont want to sound like a dick head here but IHO the flat/convex done properly with the right HT will out cut chop flat out preform a scandi knife/chopper....but dont take my word for it do some testing for yourself, i just make knives for a living what do i know

 

[Brian Ayres]

Thank you. The secondary bevels that many of you refer to is a "micro Scandi" (if you will). What you are describing is a blade that has a Scandi working edge and that working edge does 100% of the cutting.

ROTFLMFAO.... You kill me! Sigh.... I'm a Dr. I'm writing you a prescription for more interpersonal developmental therapy. Go twice week until you can play nice.

 

[Rick Marchand]

The question remains, why not just use a single bevel to zero?

Anyone???

Convex is tougher to fit into this answer but a zero grind scandi has way too much material behind the edge to be an effective slicer in most mediums. Contrary to what you may think is an obvious relation to thickness/"meat" behind the edge and strength/toughness..... you can go pretty darn thin and still retain strength. There is a reason why the industry norm is what it is. Specialty uses aside, the secondary bevel geometry seems to rule the roost on popularity among users.

 

[BMK]

Thanks, Rick. Of course there is no "best grind". Your answer makes perfect sense and I appreciate your very clear response.

I eventually settled on a near full flat/slightly convex with a microbevel. The shoulder on the secondary is less than .010" on slicers and .010" to .025" on choppers. A full scandi/sabre grind behave like a chisel, which is why it is often favoured among bushcrafters for woodcraft. A convex edge can be very strong and efficient if done properly (very few do it properly, unfortunately). In the end, it is not so much the name of the grind as it is the way in which it is approached by the maker. I have seen scandi out perform convex... outperform v-grind... out perform... etc...

Asking which grind is better is like asking what the best tasting fruit is...

The answer is "beer", BTW.

Rick

 

[Fred.Rowe]

Thank you. Sounds complicated. Many people acknowledge the ease of sharpening Scandi and convex bevels.

My question mentions Scandi and full convex bevels. I really don't understand why secondary bevels are used at all. I hope I'm missing something.

A secondary edge is used for ease of sharpening. Imagine sharpening a big fighter with a full flat grind with no secondary grind at the edge; how can it be accomplished? Is the entire flat bevel of the blade moved across a stone? That would be difficult to accomplish. Scandi grinds have the same problem. The correct way to sharpen a scandi, is to lay the flat on a stone or belt and grind or abrade until the edge is sharp.
If you sharpen a zero edge full flat blade, using an angle of twelve degrees relative to the stone or belt you have given it a micro bevel or secondary edge. If you do the same to a scandi ground blade, it is no longer a scandi ground blade. Its a flat grind with a secondary grind at the edge.

I'm with fluidsteel; a blades ability to be sharp is dictated by its thickness at the spine and the amount of distal taper. I make grind choices relative to these two factors.

Fred

 

[chainring]

Nathan expresses my thoughts well. I don't think the diagram represents angles very well. Most scandi edges that I've seen are a steeper angle than secondary bevels, in my observation. Scandis end up with a thicker blade throughout their width, but a thinner, more vulnerable edge. Cuts like a sonofagon - as my fingers will attest - but won't hold up to opening crates of ammo!

And Rick, the answer is actually, "Dr. Pepper."

Geometry.

Everything is a give and a take, and the best choice is usually a compromise. Let's take this experiment: Let's make multiple knives out of 2" tall 1/4" thick steel in varying geometries.

First, let's do a full height flat ground, zero edge form. That edge is going to be wickedly sharp. However, the geometry behind the cutting edge leaves the edge more vulnerable to damage (i.e. it's thin behind the edge).

Next, lets do a scandi type (still zero edge), with the bevel only coming up 1/3 of the height of the blade. Now that will still be pretty sharp at its edge and have a bit more protection from damage with the increased thickness, but the geometry above the edge is different. It will be more obtuse than the first knife we made, and thus its performance in certain tasks is diminished.

Now we do a full flat ground blade, with a very small secondary bevel. The edge will be sharp enough for what we need it to do (as long as we aren't shaving our face with it), it will have a bit of meat behind the edge for protection against damage, and the geometry above the cutting edge is better than our scandi grind for improved cutting performance in certain tasks.

For a general purpose type of knife (which most consumer grade knives out there are), the secondary bevel often has the best compromise of edge holding and cutting geometry.

As for sharpening, let's consider some of today's modern alloys with high wear resistance. Sharpening a very small bit of steel on a secondary bevel is much faster than sharpening a big bevel on a scandi or full-flat grind. It may be easier to hold the bevel consistently with those types of grinds, but it's going to take some work to remove steel along the entire width of the bevel to get it sharp.

--nathan

 

[Robert Dark]

Here is a pic of one of my blades and my hairy arm.

Daniel, there is way too much hair on your arm for a "REAL" knife maker. A true knife maker would either have burned it off at the forge or shaved it off testing his blades. Of course, you could be one of those fast hair-growin' magilla-gorillas.

Robert (whose burned and shaved arms are as slick as glass)

 

[Bo T]

Lets take my Mora #1. It came with a 20 degree scandi edge. It sharpened up slowly-by hand. But it was very sharp. For many tasks the 20 degree edge was great. But, with high carbon steel at Rhc 60 the edge chips easily. So now I have an edge with a couple of nicks in it. If I maintain my 10 degree bevel while sharpening by hand it will take quite a bit longer to sharpen out the nicks than it would by increasing the bevel to 17 degrees. And a 34 degree edge is less prone to chipping than a 20 degree edge. So I removed the chips by putting a 34 degree edge on my # 1 in 15 minutes +/- instead of a lot longer sharpening to a 20 degree edge. This micro bevel isn't very big so it sharpens up quickly in the field because very little metal needs to be removed. As the micro bevel gets larger I can clean up the 10 degree bevel as time permits keeping it nice and smooth and keeping the micro in micro bevel.

 

[BMK]

Bo T,

I don't think its reasonable to use a 20 degree Scandi edge as a point of comparison since (in my neophyte universe) most Scandi bevels are ~25 degrees.

 

[David Sharp]

Bo T,

I don't think its reasonable to use a 20 degree Scandi edge as a point of comparison since (in my neophyte universe) most Scandi bevels are ~25 degrees.

Not to be argumentative but who said a Scandi is 25 degrees? Please site your source. I have a collection of straight from Scandinavia Scandi blades and I can't say that conclusively.

David Sharp

 

[Fred.Rowe]

Not to be argumentative but who said a Scandi is 25 degrees? Please site your source. I have a collection of straight from Scandinavia Scandi blades and I can't say that conclusively.

David Sharp

Twenty five degrees is the accepted average for a Scandinavian grind. Since scandis only go part way up the blade they need to be fairly steep. Consider the fact that the accepted sharpening angle on many knives is 12 degrees, very close to the bisected scandi angle of 12.5 degrees. It works.

.Fred

 

[Daniel Fairly Knives]

Daniel, there is way too much hair on your arm for a "REAL" knife maker. A true knife maker would either have burned it off at the forge or shaved it off testing his blades. Of course, you could be one of those fast hair-growin' magilla-gorillas.

Robert (whose burned and shaved arms are as slick as glass)

Ahhh, you need to see the other side of my arms, they are patchy lol... I always burn my thumbs but that's about it, lol... no forging for me. Now cuts... um I have a few always! My phonebooks and cinderblocks are trashed though, as well as lots of trees around my property. It is fun!



BMK, scandis can't handle torsional forces as well as a thicker blade with a microbevel. Ferraris can't handle off roading and Hummers aren't the fastest car ... it's all good.

By the way, you have been coming up with some good looking knives that look like they would work very well for tons of tasks, keep up the great work.

 

[lazlo]

Contrary to what you may think is an obvious relation to thickness/"meat" behind the edge and strength/toughness..... you can go pretty darn thin and still retain strength. There is a reason why the industry norm is what it is.

When you say "industry" do you mean custom knives? Mass produced knives seem to have much thicker edges, which I presume is because they have mass produced heat treat?

 

[Rick Marchand]

When you say "industry" do you mean custom knives? Mass produced knives seem to have much thicker edges, which I presume is because they have mass produced heat treat?

I mean ALL knives lumped together in one heaping pile of pointy, pokey, slashy, stabby loveliness..... The knifemaking industry in general.

I don't see the relation between production knife shoulder thickness and heat treat, bud?

 

[BMK]

It would be interesting for Bark River who uses convex grinds (I believe) exclusively and Fiddleback who seems to like the Scandi bevel weigh in here.

 

[Rick Marchand]

Those are two good examples of folks who can grind a proper convex.:thumbup:

 

[BMK]

Thank you for your responses and kind words regarding my work. You made this a very interesting discussion.

 

[RyanW]

I think the reason is two part

1. Purpose - what is the knife going to be doing and that is answered in the meat of the blade.

2. Sharpening - by the end user, it is hard for many users to touch up a full convex (no secondary, Micro, Scandi Bevel) when needed. if a micro bevel is put on it they can easily sharpen it.
In fact I would guess most convex blades go out from the maker become Convex with a micro bevel pretty quickly.

 

[BMK]

The misconception about sharpening convex and scandi bevels is fascinating.

1. Convex: get a piece of leather, put some polishing compound on it and move the blade over the leather.

2. Scandi: lay the bevel flat against some abrasive and move the knife - as close to a no brainer sharpening operation as you can get

Both are actually easier to sharpen than any micro or secondary bevel where the angle is a mystery, jigs are often used and maintaining the angle is a conundrum.

 

[Stacy E. Apelt - Bladesmith]

I have read most of the posts, but if I missed this being posted, sorry for the duplication.

What is being missed by most posters is the fact that the HIGHEST angle possible on a full flat grind is very low. For instance, a 1/4" thick spine with a 1.25" blade width will yield an 11 degree edge. Make that blade 1/8" thick, and the edge is less than 6 degrees. If you do the grind as most are saying , that is the highest angle possible. To get a 20 degree edge on that blade would require the blade to be nearly 1/2" thick. Do the math if you doubt me.

Now, I think all will agree that a 6 degree edge will not last more than a few cuts.....but is incredibly sharp.
If we add a micro-bevel to the edge at ,say 15 degrees included angle, we get a much stronger edge but still retain the thin blade section right behind the edge. This will cut very well, and last longer. A fillet blade is made like this. The edge can be re-sharpened without re-doing the entire bevel. Make the secondary 20-25 degrees and we have a very useful edge for general cutting.


Personally, I think the term "Scandi" is horribly misused and not understood by most makers. A Scandi is a "Scandinavian" grind....used on Scandinavian Knives. This is normally a sabre grind to the edge with no secondary. The full flat grind was rarely used, and only on very narrow blades like fillet blades. Calling the grind on any blade wider than 1" a Scandi is somewhat silly. Most I have seen are closer to 3/4". If we do a true scandi grind on a blade that is 1/8" thick, and the grind is 1/2" high, we get a 15 degree edge.

As said, re-sharpening a Scandi requires the entire blade surface to be re-ground. This is not efficient and most people just add a small secondary to a knife with a true Scandi grind.......so it isn't really a Scandi after the first sharpening, is it.
If there is any polish or fine finishing to the blade, it will be ruined when you resharpen a Scandi. All true Nordic blades I have seen or own, have a matte finish, caused by the entire surface being lapped in the sharpening process.
Most look worse than a $5 tackle box bait knife as far as scratched bevels go.