Can someone explain a secondary bevel? >>

[patrickb]

I'm fairly meat-headed when it comes to sharpening, hence the Sharpamker sitting on my desk :~) And while I can get a decent edge on most of my knives, I really don't understand what I'm doing to effect the edge.

Simply, I'm removing metal to form a V, in which the bottom of the V forms a sharp edge. Does that sound about right? Where I'm confused is when I hear terms like primary & 2ndary bevel and how they relate to the working edge and more importantly a sharper knife.

I recently tried to reprofile a knife that wasn't sharp and didn't have the same angles as my sharpmaker. Using a 1" x 6" diamond hone, I leaned it against my sharpmaker's rod and used the same stroke as usual. I'd tried sharpening several times on the 30 deg side but was never able to get a decent shaving edge on the knife (D2). I later took Thom Brogan's advice and sharpened for a while on the 40 degree side using the diamond hone, then the sharpmaker rods and in the end I finished up with the 30 deg side.

Voilà! A shaving sharp edge. This happens to be the same advice offered the in the video so I clearly should have RTFM better than I did. I'm wondering if someone can explain how this 2ndary bevel comes into play and why it worked so well in my case above.

 

[Dcon67]

Actually by your description, you did it backwards....The primary bevel (ab angle, which in your case with a sharpmaker would be 30* inclusive, 15* per side as in the diagram) is to thin the blade so that there is less resistance when cutting, and the secondary bevel (cd angle, at 40* inclusive) has to be at the larger angle, or you would be sharpening the "shoulder" and re-profiling rather than actually sharpening the edge. The secondary bevel is to aid in removing the burr from the primary bevel, and to make the final edge stronger and longer lasting.

 

[Nosmo]

Here is a picture of a blade in the process of being sharpened. There are two angles being used. The 15 degree angle is behind the
actual cutting edge and I refer to this as the secondary bevel.
The actual cutting edge, or primary bevel, is 17 degrees and is shown in the picture as a thin line. Excuse the quality of the picture.
It is very small, but this is the edge that does the work and this blade would be reffered to as having been sharpened to 17 degrees.

Now the advantage of the secondary bevel is that the steel has been thinned down behind the actual cutting edge, there bye
allowing the blade to 'slice' more easily. Now there will be times when you need more metal behind the edge, for tough jobs,
and then a different combination of angles might be selected.

If you are interested in all this, then you are on your way to purchasing an Edge Pro Sharpener with infinite angle adjustment.

 

[Steve Hayden]

This is much the same principle as convex edges and works really well as dcon said.

Just FYI you can type the ° symbol by holding the Alt key and typing 248.

 

[ColoradoDave]

Just want to mention ... John Juranitch (Razor Edge Systems) uses the terms "primary" and "secondary" exactly opposite of what most (?) of us on BFC do: i.e., he refers to the smaller, final cutting edge as the primary edge, and the relief bevel as the secondary edge -- http://www.ameritech.net/users/knives/Juranitch1977Feb.htm

Personally, I find myself thinking more and more in terms of "relief" bevel(s), and final cutting edge "microbevel," for sake of clarity. Either way, it's probably a good idea to make sure of nomenclature being used when discussing sharpening.

BTW ... excellent illustrations, Dcon and Nosmo.

Dave

 

[mete]

Dcon explains it well. The scandinavian grind is one where you sharpen the entire bevel. My scandinavian blades run 20-30 degrees which is fine for that except for my puuko which is only 16 degrees.That it too fine an angle for a durable edge so it has a secondary bevel of about 25 degrees.

 

[Nosmo]

Just want to mention ... John Juranitch (Razor Edge Systems) uses the terms "primary" and "secondary" exactly opposite of what most (?) of us on BFC do: i.e., he refers to the smaller, final cutting edge as the primary edge, and the relief bevel as the secondary edge -- http://www.ameritech.net/users/knives/Juranitch1977Feb.htm

Personally, I find myself thinking more and more in terms of "relief" bevel(s), and final cutting edge "microbevel," for sake of clarity. Either way, it's probably a good idea to make sure of nomenclature being used when discussing sharpening.

BTW ... excellent illustrations, Dcon and Nosmo.

Dave

I think the confusion over the years stems form the dictionary definition of the word 'primary'. The Oxford dictionary says both "Earliest in time or order"
and "Most important,chief"

In the context of describing knife sharpening bevels, the meanings contradict each other.

I like your idea and terminology........

 

[blademan 13]

Mete does a good job explaining this IMO. A scandi grind has a single "primary" bevel. Some choose to reinforce this edge with a more durable, obtuse "secondary" bevel. I agree with the assumption that it is the order the bevels are created, the same way used to describe grinds on a blade.

 

[patrickb]

Actually by your description, you did it backwards....QUOTE]

You are exactly right. I explained it backwards in my original post. Appreciate the clarification and wonderful diagrams. Thanks a bunch to you both!

-pb

 

[patrickb]

Just FYI you can type the ° symbol by holding the Alt key and typing 248.

I've always wanted to know how to do that. Thanks for the tip.

-pb

 

[Geode]

Dcon67 and Nosmo - most excellent posts!

 

[panella]

Nosmo and other EdgePro users:

I'm an EdgePro veteran. I get razor sharp edges fairly easily. But I rarely put a secondary (or "microbevel") on my blades for fear of screwing up the already fine edge I've attained. Is there a special technique to use? Do you set the EdgePro a few degrees higher (more obtuse - e.g. from , say, 15 degrees to 17 degrees)) and go for a burr? On such a small edge this doesn't seem right.

As I said, I know how to get a great and lasting "V" or Scandi grind. How do I approach the microbevel?
Thanks.

- Paul

 

[Nosmo]

Well here goes panella.
Lets say that you have a blade with a single bevel of 17°.( looks like the solid line in picture A ).

Now if you want to thin the blade, but you do NOT want to change your cutting angle of 17°, this is what you want to do.

Set the Edge pro to 15° and start work. Your nice sharp edge will not be touched as you will be removing metal as per the dotted line in Picture A.

Stop removing metal before you get too close th the edge. Only remove the green amount as in picture B.

Now the second scenario might go slightly different.
Lets say that you have a blade with a single bevel of 17°.( looks like the solid line in picture A ).
Now you are not happy with this angle as for the work it does it keeps chipping and you want to increase the angle.

Then set the Edge Pro at a greater angle ( 19° or 21° as an example )
and cut in a new edge.

Don't remove too much.
Just enough to make a nice new edge.

 

[panella]

Much thanks Nosmo. Great pics! I think I'll go with plan A where you don't reprofile the initial edge.

I've used the second method you described a few times on some larger fixed blades with varying success. Problem is that I felt that I was always guessing about what grits to use and sometimes ended up oversharpening and screwing up a super edge.

 

[Dcon67]

Also there are a lot of nice advantages to sharpening it that way.....It allows you to make that nice mirror finish on the primary bevel, and still play with the grits on the final edge without messing it up.....i.e. using a med grit to make it a little toothier if you plan on cutting a lot of rope.

It also makes resharpening a breeze, you can resharpen just the secondary bevel several times before having to touch the primary bevel, and since the surface area you are sharpening is so small it only takes a few minutes to do it.

Myself, I take it another step.....I initially sharpen a knife (a daily user) with my Edgepro at a primary bevel of 15 then a secondary at about 18 .Then once it dulls, for the next 3 or 4 sharpenings I use my Sharpmaker at a 20 setting which again, only takes a few passes to bring up the burr due to the small surface area actually contacting the stones. This effectively creates a triple bevel.....Until its time to dig out the Edgepro and work on the secondary again.....eventually you will have to reprofile the primary bevel as you work your way up the blade with sharpenings.

This may sound confusing and like a lot of work, but to contrary, I do it that way to make it easier on myself. It takes a long time to get that nice polished edge, with the nice even grinds, and if I had to redo that everytime I wanted to resharpen the knife, I would put it off. By using the additional bevels, I can resharpen it to hair poppin sharp in minutes. At least thats my reason for doing it.

 

[Crayola]

My take on nomenclature:

Usually when making a knife you really don't differentiate between "blade" geometry and "edge" geometry, since when designing/making a knife you consider them together. Afterwards though, users usually separate them.

Take a "scandi" ground knife, the classic puuko with a single bevel, also known as a zero grind. In this case I'd say there is a promary bevel, which also happens to be the edge bevel. Now lets say the puuko's grind is at 12 degrees per side, and you decide to touch up the edge on the 30 degree setting on the sharpmaker. Now you'd have a primary bevel, and a secondary bevel, the first WIDE one at 12 degrees per side and the second TINY one at 15 degrees per side. Now if you touch the edge up again a little at the 20 degree setting, you'd have a primary, secondary, and tertiary bevel. Th emore bevels you add, the more you count.

Now, usually the end user though does not include the initial blade grind into the math. So if you take a knife and flat grind it, and then put on an edge bevel, people usually count that edg bevel as #1, or call it a primary edge bevel. Say you sharpened that at 15 degrees per side and want a quick touch-up, or you need to make it a bit stronger. You might touch the edge up on the 20 degree setting of the sharpmaker, so you would have 2 bevels at the edge (remember, we are ignoring the main blade grind). This 20 degree bevel people call a secondary bevel, since it is a second angle at the edge. For those not counting the exact numbers and are more describing its function, they call it a micro bevel: it is just another little bevel there to strengthen an edge, or make sharpening faster, etc.

In the whole grand scheme of things, I like to count all of the bevels, and not just because I make knives! All of the bevels are there for a reason and play a part in a knife's function, so I count 'em all to give them all fair consideration. When my flat ground knives end up getting too thick from repeated sharpening, this tells me it is time to readdress the primary bevel, that main knife blade bevel. Juranich's solution ofr folks at home is just to grind in a big relief bevel, thinning the knife out a bit. I just take the knife to my grinder and thin the whole main bevel out, to make sharpening that much easier down the line. For those without grinders, large coarse hones for grindign in relief grinds works too, so don't worry! But I do recommend counting all of the bevels.

I hope this helps!

 

[Nosmo]

After reading Dcon67's and Crayola's post above, I see where you both are coming from as to nomenclature.

From a knife makers prospective I can see the reasoning in referring to the first bevel that is ground in as the primary bevel.

From a users prospective, I can understand him looking at a blade with two ( example ) very obvious bevels,
and concluding that the cutting edge is the primary bevel and the other the secondary.

 

[Crayola]

Nosmo:

Exactly! Makes sense, but creates confusion eh! One way orders them from the order they are made, the other is more of a function thing - which bevel is doing the work for me? - that kind of thing. The confusion is when people try to talk with eachother and use different nomenclatures!

 

[Thomas Linton]

Mete does a good job explaining this IMO. A scandi grind has a single "primary" bevel. Some choose to reinforce this edge with a more durable, obtuse "secondary" bevel. I agree with the assumption that it is the order the bevels are created, the same way used to describe grinds on a blade.

Funny thing about the "scandi grind." Very few knives made in Scandinavia have the "scandi grind" and most of the minority that do come from Sweden. This is acknowledged by makers from that area. For example, the knives from Iisakki, the largest Finn maker ( I have six) , all come with a final microbevel. I have three Helle knives from Norway and all came with a final microbevel. Ditto my Roselli and three Hackman knives. As a result, if you don't know what is meant by "Scandi grind" and rely solely on what is actually produced by "Scandi" makers, you might easily be confused.

 

[Steve-O]

I too have been confused by words, when someone says primary, secondary or scandi I do not always know what they mean.

But in my head, I know what I like, it is simple. Regardless of the original grind (on a dull pocket knife) you need to thin the blade, then give it an edge.

Depending on the thickness of the blade and the original grind and your purpose, these two steps can be easy, a bit of work or hours of pain.

Even the degrees of sharpening can be confusing..I prefer the single sided ones...15° rather than 30°. Standardization would be nice.

Most of my knives are folders not meant for hunting, and here are my thoughts.

Thin the blade edge (from original grind) to 15° to 17°, this makes the blade thin which will cut/slice very well, but depending on use and materials, may make it weak.

Thin the blade edge (from original grind) to 18° to 22°, this keeps the blade around what most manufacturers suggest, produce and is tougher.

But keep in mind - You can't put a 15° edge on a blade that has a 20° bevel. I have several small, thin pocket knives that I keep at 11° to 15°, most larger knives I try for 16° to 18°...sometimes it takes a while. My one Sebenza is down to about 20°, even with the hollow grind; damn that BG is tough stuff.

Angle means little, you can have a super sharp knife with a 20° edge (with the right materials), angle mostly tranlates to toughness.


Hope this helps,


Steve-O