Why secondary and micro bevels?

[BMK]

A question only a fully committed neophyte like me could ask:

Why do many knife makers grind a secondary or micro-bevel as opposed to ginding a single angle or curve as in the case of a Scandi or full convex bevel?

Every time you resharpen a micro-bevel or secondary edge, blade geometry changes. With the Scandi and full convex bevel, edge geometry remains constant through sharpening cycles.

I have not seen the numbers but I bet there is less friction when separating material if there is no secondary edge or micro-bevel. If someone has access to these numbers, I would like to see them.

If material separation is what a knife is designed to do, then why use secondary and micro-bevels?

Thanks for your ideas. Fire away!

 

[Sparljo]

Its easier to sharpen and keep sharp. Very few blades will hold up with a true zero ground edge.

Think of a Scandi grind as a magnified version of a micro bevel.

 

[JasonSCarter]

Not to be rude, but Strength... that should be obvious. A scandi grind is perfect for strait razors, or knives that are primarily slicers. Ever see the edge flex test for one of those? Now try that with a hunting knife. The edge wont flex due to the extra "meat" just over the top of the edge. it's much more rigid. Able to take impacts/greater applied force with out or with VERY little deformation.

Jason

 

[BMK]

If, as explained above, a Scandi grind is "a magnified version of a micro bevel", then a Scandi is actually stronger because it has more steel behind the working edge. I have two zero ground edged knives in front of me right now - one is a Scandi and one is a full convex grind. Both are very strong and hair popping sharp.

There are at least 100 secondary or micro bevel knives out there to every one Scandi or full convex knife. There must be a reason for the ubiquity of secondary beveled blades.

This is about as fundamental a question that can be asked about knives and so far, I don't understand.

 

[Daniel Fairly Knives]

I do both, it depends on the knife. I like micro bevels because they are strong and easy to sharpen. They do well with torsional forces... won't chip as easily when twisted. Zero bevels are great slicers and can be very strong also, there are a million ways to grind a knife.

So I say as long as they are good knives then that is what is important, some can be performance oriented in one direction or just overall good knives, there a lot of ways to do it.


Here are some of my odd grinds.

I think the knife is called a kata-kira-ba... it is a zero bevel chisel grind with a tiny convex to it.

This one is a .360 thick chopper ground to a near zero bevel.

Two more... The small Ti one is a zero bevel like a scandi but chisel ground and the big chopper is a near full flat grind with a convexed tip... large microbevel for chopping but it will still cut thin paper no problem.

 

[james terrio]

I like zero-edge convex grinds on big knives, but most guys don't have belt grinders and a variety of belts to play with for touching them up. Or they may just be afraid to scuff up a nice-looking expensive knife. A micro-bevel is easy to sharpen with a bench-stone or Lanksy/Sharpmaker etc.

 

[Drew Riley]

Not to be rude, but Strength... that should be obvious. A scandi grind is perfect for strait razors, or knives that are primarily slicers. Ever see the edge flex test for one of those? Now try that with a hunting knife. The edge wont flex due to the extra "meat" just over the top of the edge. it's much more rigid. Able to take impacts/greater applied force with out or with VERY little deformation.

Jason

Agreed. If you draw a "magnified" version of a scandi grind, vs. a full flat grind with a secondary bevel, it should be very obvious that there is more steel behind the latter. It may not slice as well as a zero edge, but it will hold up to a lot more abuse before rolling or chipping, with all other things (heat treat, temper, steel type) being equal.

 

[BMK]

Agreed. If you draw a "magnified" version of a scandi grind, vs. a full flat grind with a secondary bevel, it should be very obvious that there is more steel behind the latter. It may not slice as well as a zero edge, but it will hold up to a lot more abuse before rolling or chipping, with all other things (heat treat, temper, steel type) being equal.

More steel behind the flat grind with a secondary bevel of the same angle as a Scandi bevel? Take a look:

#2 is flat and #3 is Scandi

 

[Drew Riley]

More steel behind the flat grind with a secondary bevel of the same angle as a Scandi bevel? Take a look:

#2 is flat and #3 is Scandi

According that picture, I'd say 2 was a full scandi (weakest edge of all) 3 was a partial scandi (a big stronger but not as good of a slicer as 2) and 5 was closest to a flat grind with a secondary, albeit a partial flat grind. 5 has more steel behind the edge, compared with 2 and 3.

5 might not be as good of a slicer/peeler as 2 or 3, but it will hold up the longest under chopping, impacts, and hard cutting.

 

[thegeek574]

More steel behind the flat grind with a secondary bevel of the same angle as a Scandi bevel? Take a look:

#2 is flat and #3 is Scandi

that is one of the more obtuse scandis that oi have seen. also, he was referring to a FFG with a secondary bevel. that would make it significantly stronger.

 

[BMK]

I fail to see how any flat grind with no secondary bevel can be more obtuse than any Scandi beveled at a standard 20-30 degrees. The fact of the matter is: Scandi grinds have more steel behind the working edge and more steel in the blade (period) than a zero beveled flat grind with no secondary bevel.

 

[BMK]

I fail to see how any flat grind with no secondary bevel can be more obtuse than any Scandi beveled at a standard 20-30 degrees. The fact of the matter is: Scandi grinds have more steel behind the working edge and more steel in the blade (period) than a zero beveled flat grind with no secondary bevel.

 

[Brian Ayres]

More steel behind the flat grind with a secondary bevel of the same angle as a Scandi bevel? Take a look:

#2 is flat and #3 is Scandi

Monkey,monkey monkey....tsk tsk tsk.
Lol, you've been getting along so well.... :thumbup: #2 is a zero edge the same as #3... As stated, #5 is a flat grind with secondary bevel. Granted, the profiles are for illustration purposes as their geometry isn't exactly great.
For a serious answer to why everyone doesn't do scandi grinds... As James said, they're hard to sharpen well. I owned two knives with scandi grinds like the ones you make when I was a teenager and added a secondary bevel to both...

On another note. I admire seeing your progression as a knifemaker over the last few months. Adding a plunge line to some of your knives to keep the sharpened blade out of the finger choil is nice.:thumbup::thumbup:

Different blade geometries serve different purposes. So, say we have two knives, both O-1 with the same heat treatment, and a full flat grind with a secondary bevel. One, an 1/8"x2"x10" bladed kitchen slicer vs a 1/4"x1"x4" bladed full flat grind with a secondary bevel. Both are the same blade style, but the geometry and slicing ability are vastly different. Also, the second blade will stand up to more lateral strain than the first knife. Make the same knives with a 12 degree scandi and they will still be different blades in performance...

In summary, different edges for different purposes... I'd take a hollow grind straight razor over a scandi at my throat any day of the week.

 

[BMK]

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.

Monkey,monkey monkey....tsk tsk tsk.
Lol, you've been getting along so well.... :thumbup: #2 is a zero edge the same as #3... As stated, #5 is a flat grind with secondary bevel. Granted, the profiles are for illustration purposes as their geometry isn't exactly great.
For a serious answer to why everyone doesn't do scandi grinds... As James said, they're hard to sharpen well. I owned two knives with scandi grinds like the ones you make when I was a teenager and added a secondary bevel to both...

On another note. I admire seeing your progression as a knifemaker over the last few months. Adding a plunge line to some of your knives to keep the sharpened blade out of the finger choil is nice.:thumbup::thumbup:

Different blade geometries serve different purposes. So, say we have two knives, both O-1 with the same heat treatment, and a full flat grind with a secondary bevel. One, an 1/8"x2"x10" bladed kitchen slicer vs a 1/4"x1"x4" bladed full flat grind with a secondary bevel. Both are the same blade style, but the geometry and slicing ability are vastly different. Also, the second blade will stand up to more lateral strain than the first knife. Make the same knives with a 12 degree scandi and they will still be different blades in performance...

In summary, different edges for different purposes... I'd take a hollow grind straight razor over a scandi at my throat any day of the week.

 

[Carl_First_Timer]

I'd say scandi Grind, at the same angle of a secondary bevel, is stronger. However the secondary bevel has a weight advantage. The weight loss to strength gained ratio would seem to be advantage secondary bevel.

EDITED to add: A scandi and Secondary bevel all being the same will chip out just as much as each other, up to the full same angle.

 

[Brian Ayres]

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.

Well, in cutting tests, the convex blades have a tendency to hang up on stickyish media. Such as cutting rubatex pipe insulation.(I know, I know, who cuts much rubatex in real life???) Convex grinds are very strong, and often the first choice for choppers. A flat grind on a kitchen knife vs a convex grind on the same knife would cut cheese without sticking better. It's all about geometry. Blade width, edge type and blade thickness and blade grind will all create variables that make one blade profile better for one purpose than another even with the same exact material and heat treatment.

 

[silver_pilate]

I really don't understand why secondary bevels are used at all

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

 

[Lon Humphrey]

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

 

[silver_pilate]

And a note on friction....

Most consumer grade, mass-produced razor blades have a secondary bevel for the reason that it decreases friction during the push cut. A straight edge will tend to push into a substrate and the separated substrate will just ride up the large bevel on either side creating friction. A microbevel will tend to cut the substrate and then part it, keeping the substrate just above the cut off of the large bevel on either side and reducing friction.

So on a very small level, a microbevel may actually reduce friction a tiny bit.

--nathan

 

[Rick Marchand]

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