Some general Sharpening questions about angles, bevels, etc.

[jtice]

I know that this much be in about a million other threads here,
but I had a few specific questions I would like to ask.

I have been into knived for a while and have always sharpened my own knives.
I currently have a Spyderco Sharpmaker, but I have an EZE setup on the way.

I have always just gone by the edge angle, ussually about 25 to 30 degrees.
But, I have heard people talking about alot more than just the edges angle here.
There was mention of 0.035" I am not sure what that means, and what part of the blade/edge it pertains to.

I have also heard mention of "micro bevels"

I am getting the feeling that some of you are putting double edges on your knives. Having a wider angle at the very edge, so that it is easier to touch up the blade?

Can you give me a rundown on this stuff?
and give me a general guideline to follow for certain blades?
I mainly have 3 types of knives, and 3 types of edges I like them to have.

Folders: main EDC BM 710 M2 - I like a very very sharp edge, used for box cutting, light wire stripping, rope and string cutting, and defence.

Small Fixed Blades: BM Nimravus M2 - I like to keep this one very sharp also, but with more of a rugged edge. Used for rope, small branches, plastics, beer/pop cans, defence.

Large Fixed Blades: Ranger RD9 - used for very heavy chopping of branches and logs, slitting, etc.

Thanks alot
~John

 

[Cliff Stamp]

There was mention of 0.035" I am not sure what that means, and what part of the blade/edge it pertains to.

Usually the thickness of the edge, measured behind the bevel.

I am getting the feeling that some of you are putting double edges on your knives. Having a wider angle at the very edge, so that it is easier to touch up the blade?

Generally, it is much more efficient to raise the sharpening angle when you switch abrasives to improve speed of sharpening. This is almost standard for chisels because the edges are so wide you really don't want to polish the whole thing, it takes way too long.

Folders: main EDC BM 710 M2 - I like a very very sharp edge, used for box cutting, light wire stripping, rope and string cutting, and defence.

You can strip wire with a very low angle if you do it carefully. My small Sebenza can strip a standard tv cable with no visible effect on the knife. The primary edge is set at about five degrees, sharpened flat to the stone basically and there is a very small micro-bevel you can't see set at 20 degrees on the Sharpmaker.

If you want to do really fast, which can involves cutting into the wire core and pulling on the blade to strip off the wire, this can stress the edge laterally and thus you will want more of an edge bevel, about 10/15 and or even 10/20 if you are really aggressive and the more obtuse bevel would be significant, not under 0.010" or so in the micro-bevel.

For cutting soft materials like rope and cardboard there is no limit to M2 in general, it is a very fine grained steel.

Small Fixed Blades: BM Nimravus M2 - I like to keep this one very sharp also, but with more of a rugged edge. Used for rope, small branches, plastics, beer/pop cans, defence.

The beer / pop cans is the sticking point there, depending on how you are cutting it, very fast cuts and torques are more demanding, but it sounds close to a 10/15 profile in general.

Large Fixed Blades: Ranger RD9 - used for very heavy chopping of branches and logs, slitting, etc.

A decent profile to start off with is 15/20, you then tune this to the local wood and your exact methods, the 20 part should be about 0.020" thick to start. You gradually reduce this and start watching the edge, at some point it will start to turn a little on the harder wood working. If you go down gradually, a degree or so, you will catch the deformation so it happens just lightly.

Once you do these mods on a few knives you start to get a fell for what your experience and strength require and it is much faster to optomize new knives as you have a much better idea where to start. I didn't comment on defence in the above because if you actually want the edges to take that kind of use without visible damage they have to be extremely obtuse because you can end up doing hard dynamic cutting into thick metals and bone.

-Cliff

 

[jtice]

Thanks alot Cliff ! Excellent post.

Now, just to make sure I understand the terms...

15/20 means the primary angle is 15 degrees per side, and the very edge is 20 degrees per side?

Does using these dual angle edges have any other advantage, other than just making it easier to sharpen and maintain?

This is very new to me, I have always just picked an angle (usually 25 to 30 degress) and just sharpened the edge to that.

I have never had a problem with the edge getting real wide, and it making it harder to sharpen, and polish with the finer stones.
But, I have not done a 1/4" thick blade yet either.
I can understand that with a blade that thick, you could end up with an edge over 1/8" wide, and have alot of surface there to polish with the finer stones.

Would there be any downfalls to doing that though?
I have seen a few photos of the entire edges polished down, and it looks fantastic.

I am surprised to hear that you are using such a low angle (10/15) for knives used to cut cans etc.
I thought 20 was pushing it for things like that. Seems I have been using much wider angles than I need?

~John

 

[Cougar Allen]

 

[jtice]

Opps, sorry about that.
Still getting used to the forums setup and catagories.
Dont know how I missed that.

 

[Cliff Stamp]

15/20 means the primary angle is 15 degrees per side, and the very edge is 20 degrees per side?

Yes, in some case the micro or final bevel is just the honing angle. You can't see it because it is set by a few passes on a stone and will only be about 0.1 mm wide. Most micro-bevels on cutting tools are this width because generally the forces are fairly low and thus only the very edge tends to turn or compact.

On chopping tools the secondary bevel isn't really micro, you can usually see the distinct more obtuse edge bevel. Many people run convex bevels on these types of knives and if you look down the edge signthing along the underside of the grip, you can see the curvature increase signficantly towards the very edge and taper back to parallel in the shoulder.

Does using these dual angle edges have any other advantage, other than just making it easier to sharpen and maintain?

They allow you to better tune the cutting ability and durability. Generally the forces materials exert on an edge tend to be focused on the very edge and fall off dramatically above it. Even though at the very edge you may need 15 degrees to stop it from twisting, once you go past a certain thickness you don't need this obtuse bevel anymore and you can thus reduce it. This is in general why knives have distinct primary grinds and not just one bevel on flat stock.

I have never had a problem with the edge getting real wide, and it making it harder to sharpen, and polish with the finer stones.

How long on average does it take to sharpen a blade? Assume it is really dull, say you dug a hole in the ground with it, or cut up a lot of used carpet. With use of microbevels you can actually take this to a finish polish in 1-2 minutes on a four inch blade and the blade will push cut newsprint (assuming a nice steel, no floppy burr issues).

I can understand that with a blade that thick, you could end up with an edge over 1/8" wide, and have alot of surface there to polish with the finer stones.

Yes, they can even get wider, 1/4" wide or so edges isn't uncommon and on some convex bevels the grind runs the width of the knife so you really don't want to finish hone the entire thing.

Would there be any downfalls to doing that though?

Micro-beveling in general, no. Making an edge too wide, yes. If you go below a certain angle the edge will just collapse because it no longer has the strength to stay rigid.

I am surprised to hear that you are using such a low angle (10/15) for knives used to cut cans etc.

Pop and beer cans are really thin and soft, I can cut them with my small Sebenza with the above profile and there will be no damage visible under 10x magnificantion. The edge will still push cut newsprint though you will notice a small loss in sharpness. Food cans are not much more difficult if you cut them taking care to minimize the torque across the edge.

Trying to cut a curve is really difficult as you are essentially prying the metal apart with the edge, just cut a + sign in the top and pry it open. If you start twisting in the metal you will want a more significant extent of micro-bevel but it doesn't need to be much more obtuse. 20 degrees in general is a really high bevel.

Normal hardwood felling axes for example are around 15 degrees in the final bevel, and only at that angle for the last bit of the edge and quickly sweep back to lower angles. On softer steels you will have to increase the edge angles significantly because the strength is lower. Carving hardwoods for example you can go a lot lower on 66 HRC 1095 than 54 HRC 420J2 for example.

-Cliff

 

[HoB]

Cliff, for your second to last word, I think you meant to use 'less' not 'more'.

On the can cutting: I agree with Cliff, even a thicker food can can be cut with a pretty acute edge. Important is though, that you do not side load the edge. Because of the localized stress, you can easily break out LARGE chips out of the edge, if you twist the blade inside the cut a little bit. But a decent steel that is properly sharpened (no burr) looses surprisingly little sharpness when cutting carefully into a can. If you want to cut along the rim of the can, you need a pretty sturdy edge (personally I would use even more than 20 deg per side for that), because you are constantly torquing the blade due to the radius of the cut you are making. For the cross in the lid as Cliff was suggesting you can get away with a much more fragile blade.

 

[Cliff Stamp]

Cutting a circle is pretty difficult, especially how most people I have watched do it. The best way from the point of view of the knife is to make smooth cuts starting at the point and cut to the choil in one smooth motion and gradually turn the blade in the cut. Draw the blade out after moving it back from the metal and repeat. A lot of people that attempt this with knives use them like can openers, stab and work the point around. It is usually much faster and neater to use straight cuts and it produces a lot less jagged edges. If you don't like the plus sign, just cut a square flap. Similar for opening juice cans and similar, cut notches, don't for example stab the blade in and then twist to smash all the metal out of the way.

-Cliff

 

[jtice]

Thanks alot Cliff, your responces have been packed with info, and very helpful.

So, it seems that the dual bevel has two main advantages.
It lets you keep the primary bevel at a lower angle, keeping your blade thinner at the edge.
And having the wider angle secondary bevel at the very edge, lets you have less surface area to sharpen, and less surface area that is forced though the cut.
Since the very edge is what does the actual cutting, this is the only part of the blade you really need to be at teh larger angles.

Funny you should ask about cutting carpet,
did that just last week with the M2 Nimravus.
I was very surprised at first how fast the carpet duled the M2.
But after I thought about it, it made sence. The indoor/outdoor carpet has a very gritty backing to it.

I sharpened the Nimravus on the Sharpmaker before I started.
and again after I was done. I think it only took me about 10 minutes.
Using the medium, and then the fine stones.
I think the old Sharpmaker I have is 25 degrees, but I am not sure.
Obviously, I have just the one bevel.

Only thing I dont quite understand is this...
You say the dual bevel helps you better tune the cutting ability and durability.
I suppose I can understand the cutting ability.
The edge is a wider angle, gets the material cut, and the main bevel is thinner, not being as wide as the secondary bevel makes it have a thinner profile, so it is not making the material spread apart further than it needs to.
But I dont quite understand why it would be more durable.
I would think that a 20 degree angle all the way back, would make for a thicker blade, making it stonger,
vs. the thinner 10 or 15 degree smaller/thinner bevel behind it.

~John

 

[Cliff Stamp]

I was very surprised at first how fast the carpet duled the M2.

It is pretty bad since it is usually filled with dirt, you can get much better edge life if you have a really high relief grind because the cutting ability will be higher at a given sharpness. The edge retention will also in general be higher if left more coarse. Benchmade also leaves their M2 fairly soft for M2, it is however difficult to reharden M2 because of the secondary carbide precipitation so you can't just have it reheat treated as the grain explodes when austenized. However in general there are not a lot of production knives offering better performance, hopefully when Spyderco comes out with thier HSS line they hardened it like HSS.

But I dont quite understand why it would be more durable.
I would think that a 20 degree angle all the way back, would make for a thicker blade, making it stonger,
vs. the thinner 10 or 15 degree smaller/thinner bevel behind it.

It would, however you could easily make it 15/25 which would both out cut it and have better durability on most materials. As you noted, only the very edge which is heavily loaded needs the more obtuse bevel, anything above it just lowers the cutting ability so hack that off. The real benefit is that since you have cut off all the extra metal you don't need you can raise the edge angle a little more and gain durability in the case of accidental impacts or overloading and the knife will still cuts better than before on a lot of materials. It is a tuning process, in general by optomizing where the edge needs strength and where it doesn't, multi-bevels allow a better combination of strength/cutting ability than just one bevel which has to make more of a compromise because you only have essentially one variable to work with.

-Cliff

 

[jtice]

Thank you very much Cliff,

You have explained things very well, and have been a huge help. :thumbup:

~John

 

[jtice]

Just got my EZE sharpening system.
Seems really well built. I will do alittle writeup about it in a couple weeks.

Quick question though,
What mm setting should I put the reak guide at?
Book suggest 40, but will that make my angles correct on teh front knife clamp?

~John

 

[jtice]

Just tried the EZE,
The stones took a long time to get shimmed up just right in the holders so that the rod was level with the stone.
It looks like this is going to be an issue with just about any stone though.
With the rear guide set at 40mm, and the front clamp set to 15 degrees, I tried it out on a BM 3.5" blade.
The clamp had to have one end ground down to allow room for the thumbstud.

I am not sure about the rear guides set height though,
the angle seems very small, the bevel being at least twice what it was from the factory.
I have no idea what the angle from the factory was though.

I have a suspision that I have done something wrong.
My Spyderco Sharpmaker is supposed to be either 20 or 25 degrees, I cant remember.
It doeesnt made a bevel this wide though.

Also, I noticed that the bezel does not look the same on both sides,
one is alittle wider than the other in spots.
What could have caused this?
That happens alittle on my Sharpmaker, but I figured that was due to it being more freehand.

The edge seems to be fairly nice though, got it pretty smooth with the fine side of the stone.
But, to tell you the truth, if I really took my time, I got them sharper on the Sharpmarker.
At least, cutting skin easier.

~John

 

[DGG]

John -

I'm going to come crashing into the middle of this thread. I don't think anyone should get too crazy about angles. The key I think is to make the angles consistent along the edge on both sides so they join to form a very thin line which is the cutting edge. Whether the knife is at 15 degrees per side, or 18 degree, or 20 degrees is not that critical. Consistency is important or you will never get the "BURR". I also favor a quick strop/hone when finished. For some reason this really seems to make an edge scary sharp and it doesn't cost hardly anything, take any time to do, and is very easy to do.

 

[jtice]

The knife was sharp after I finished, just not SHARP.

I made a few light passes on the fine stones with my Sharpmaker,
that really seemed to help, at least for skin cutting ability.
It made it just barely shave hair after that.

Its just going to take practice, I need to try a few other knives on it.
I am still surprised how shallow the 15 degree edge was, huge difference from 20 and 25.

Does anyone know what angle the OLD Spyderco Sharpmaker is?
I might set the EZE up to match that,
that way it will match up well when I make the finial passes on it.

Also, EZE owners, what mm setting do you have the rear guide at?
I have mine on 40mm, thats what the manual said to set it at.

~John

 

[butane216]

John -

I'm going to come crashing into the middle of this thread. I don't think anyone should get too crazy about angles. The key I think is to make the angles consistent along the edge on both sides so they join to form a very thin line which is the cutting edge. Whether the knife is at 15 degrees per side, or 18 degree, or 20 degrees is not that critical. Consistency is important or you will never get the "BURR". I also favor a quick strop/hone when finished. For some reason this really seems to make an edge scary sharp and it doesn't cost hardly anything, take any time to do, and is very easy to do.

sounds like you've read Jurantich's book

 

[Cliff Stamp]

Does anyone know what angle the OLD Spyderco Sharpmaker is?
I might set the EZE up to match that,
that way it will match up well when I make the finial passes on it.

It would be most efficient if you undercut it a little and thus the Sharpmaker would just be micro-beveling.

Also, I noticed that the bezel does not look the same on both sides, one is alittle wider than the other in spots.
What could have caused this?

The bevel changes in width along the blade? There are a number of users of this system on the SwampRat forums, hopefully you can get some direct feedback there.

Whether the knife is at 15 degrees per side, or 18 degree, or 20 degrees is not that critical.

A knife at 15 vs 20 degrees makes a large difference, Joe has described this in detail with a resharpening and getting changes of hundreds of percent by adjusting angle and grit. 10 vs 20 doesn't even feel like the same knife. This can make so much of a difference that for example 420J2 will easily have better functional edge retention than S30V (or insert some other stainless you prefer). For larger blades it is also necessary to keep the edge from folding, and for coarse steels it is necessary to keep the edge from breaking apart. Some won't even sharpen at the lower angles. See work done by Swaim, Johnston and more recently Sodak.

-Cliff

 

[jtice]

Yes the bevel is quite uneven.
It varies in width as you go along the bldes lenth,
and, the width on one side doesnt match the width on the other side.
Very strange. Thats never happend that much on the Sharpmaker.

~John

 

[DGG]

sounds like you've read Jurantich's book

Yup I did! And from forums, magazine articles, and most of all lots of trial and errror.

I'll gladly learn from a good teacher. Recently I bit the bullet and bought and Edge Pro Apex. I like the way it sharpens but hate having to soak the stones in the john for 20 minutes to get them wet before using them. I guess that's a small price to pay for a very sharp edge.

One of the things I learned are that there are many types of "cuts". Some cuts are made by slicing the knife across the material. Some cuts are made by pushing the edge into the material being cut. And some cuts are a combination of those two cuts.

"A knife at 15 vs 20 degrees makes a large difference, Joe has described this in detail with a resharpening and getting changes of hundreds of percent by adjusting angle and grit. 10 vs 20 doesn't even feel like the same knife. This can make so much of a difference that for example 420J2 will easily have better functional edge retention than S30V (or insert some other stainless you prefer). For larger blades it is also necessary to keep the edge from folding, and for coarse steels it is necessary to keep the edge from breaking apart. Some won't even sharpen at the lower angles. See work done by Swaim, Johnston and more recently Sodak.

-Cliff"

I agree 100%. But I think you/we/Joe are referring mainly to the "secondary" or "back bevel."

For the dinky primary micro-edge bevel I don't see that much difference between 18-18-20 degrees when I sharpen. Am I right in thinking that the thinner the blade the easier the cutting? I think that is why serrated knives cut so well. The edges are very thin within the serrations and cut easily into the material being cut. Is this correct?

 

[db]

“
jtice said…
and, the width on one side doesnt match the width on the other side.
Are you sharpening on one side only until you get a burr then sharpening on the other side? If so this is what can happen when you do that. Your moving the edge off center and the bevel is larger on one side than the other. To correct it next time sharpen on the smaller bevel side until you move the edge back towards the middle. This may seem like a non issue with some but it can be fixed and does happen a lot when you only grind one side to get the burr. To prevent this from happening again switch sides, every 50 or what ever you want strokes, grinding both sides until you get a burr. You also don’t even need to get a burr but that’s another method.