Sharpening Big Chopping Knives?

[Mtn Hawk]

Apologies in advance if this subject has been covered. I went back many pages and couldn't find a thread on the best sharpening method and edge geometry for big chopping knives. Seems like I remember reading some a few years ago, and may have even posted myself, but not being able to use the "Search" function is limiting. If I can get links to existing threads on this subject that would be great.

I have a big chopping knife (9.5" blade) I need to sharpen. This has a convex edge but I have been unsuccessful at sharpening it that way, although I've read and tried many different instructions. (Please, no more instructions or links, or posts telling me how "easy" this is.) I'd just as soon not convex sharpen, anyway, as most of my sharpening is done in the wilderness. It's much easier to carry a stone for freehand sharpening than pack the supplies that are needed for convex sharpening or heavy and/or bulky tools and equipment.

Most of the wood I chop (pine and fir in the Western mountains) is dead, dry, and quite hard, so I'm concerned about having enough edge durability that blade chipping, fracturing, rolling, or other damage does not occur, yet I don't want the edge so thick that chopping is not effective. Sometimes one knife is all I take, so I need an edge that is also suitable for more delicate chores such as food preparation and cleaning fish and small game.

I am thinking about thinning the edge out at a fairly low angle, which would remove the convex edge and make it into a V-grind, then putting on a 20-30 degree microbevel. This would add some durability to the edge for chopping but still leave it thin enough for finer cutting.

Please no theories or guesses about what sharpening method and edge geometry might work or should work, and I am not a "scary sharp" type. I am only interested in advice on what is practical and works best, based on real-world experience.

Thanks...........

 

[mordi]

If already convex ,no need to thin out the blade. I sharpen cleavers and large camp knives at apx.23 deg ,strong but not very delicate, good enough for basic food prep . I use edgePro. To maintain you can use sharpmaker at a slight angle

 

[siguy]

i just got a 1x30 belt sander from harbor freight, and with fine grit belts and a fine stone to break the burr, i am getting great convex edges and have even full-convex ground some saber hollow ground cheap knives.

but if you don't want to get into that (you mentioned that most of your sharpening is done in the field) then get a medium and a fine grit stone, or a combo stone. sharpen it as you described you plan on it, but don't worry about thinning it. just sharpen the edge like a v-grind edge, in a few years of sharpening the knife will become much more v-grind like. i personally finish my edges most of the time with a soft arkansas stone that i keep in my pocket.

 

[Dog of War]

For what you want to do, I'd suggest sharpening the primary edge at about 12 degrees per side, and then applying 20 deg./side microbevel. I have found this works well for most large blades used for chopping wood -- not theory, but real world results (although theory tends to support this.) The 12 deg/side primary bevel gives a noticeable improvement in chopping depth and ease over a blade sharpened at the more usual 15-20 deg/side, while the 20 deg/side microbevel makes the final edge much more durable and less prone to rolling or chipping out than if you had no microbevel, or run a more acute microbevel such as 15 deg/side.

After doing this, if you find the edge isn't holding up, it's now very easy to add a small secondary bevel of, say, 15 deg/side, giving you a multibevel edge of 12/15 deg, plus a 20 degree microbevel. The work done taking the edge down to 12 deg/side isn't wasted at all, as the multibevel edge will perform better than a single bevel edge of 15 deg/side, and maintenance sharpening will be quicker and easier because of the extra relief.

Sorry if that sounds too rigid or even theory-based, the fact is that fairly slight changes in the angle of the primary bevel, especially in the range from 10-15 deg./side, can make huge differences in the performance and durability of an edge. But don't take my word for it, try it for yourself.

As for convexing the edge, it's a matter of personal preference. The only meaningful difference in performance between convex and non-convex edges has to do with the underlying geometry and cross-section of the edge. And at more acute angle like we're talking about (compared to most factory edges at least) the difference becomes even more meaningless. So I would say, if it's easier for you to do a convex edge, do it.

 

[WhitleyStu]

Here is a link to a post I made last year on how I maintain my convex edge blades...

 

[thombrogan]

Mtn Hawk,

Don't you have a Razor Edge coarse hone and Sharpmaker for doing such things? If memory serves, your coarse hone was faster than your 1"x30" sander and may have been faster than a DMT 120 grit diamond benchstone as well.

 

[Bwilson]

I put a 15 degree main bevel w/ a 20 degree micro on my ratweiler and it GREATLY increased its chopping ability. I don't know if this matters much but for the 15 degree main I used the polishing tapes with the edgepro to put a mirror finish on it. I took the 20degree micro to only 220 because I like "teeth" for general cutting. I think the high polish on the primary helps with the chopping a little bit but I'm no expert by any means.

 

[Andrew Colglazier]

I hand sharpen traditionally with a big butcher's steel, and finish with a polish on a ceramic rod if I want to take the time.

I have no idea what degree the angle is and all that stuff, but the knives get sharp.

Andy

 

[Grampa]

Mtn Hawk -

If you check out Whitley Stu's thread, and go with the 1x30 belt grinder, you'll be getting an edge that will only need stropping in the field, not sharpening.

It takes very little time to learn how to use it, and it will put an edge on anything that should have one, faster than anything you're using now.

And oh yeah, it does convex edges beautifully!

 

[Mtn Hawk]

Thanks much for all your replies. A lot of good info here.

Dog of War-- I appreciate your advice and thorough reply. I haven't sharpened knives for a long time. Before I took off metal from a good knife I wanted to make sure that I am on the right track with my thinking. Everything you said makes sense and started to remind me of things I'd forgotten. I especially appreciate you bringing up the option of adding a secondary bevel. I probably wouldn't have thought of that.

BWilson-- Thanks for your feedback. My knife is a Battle Rat, so related to your Ratweiler. I would think that the convex bulge just above the convex edge would prevent it from going as deep into hard wood as a thin V-grind (everything else being equal). It seems to me I read that the opposite is true when cutting green wood, that the convex edge is better because it forces the wood apart more.

The problem, as I see it, is to make sure that the thinner V-grind is durable enough that it doesn't start causing edge problems during heavy use. It also seems logical that a polished edge would go through wood easier, although I don't know how I could do that while keeping my wilderness sharpening tools to a minimum. I also agree with you about keeping knife edges a little "toothy" for general cutting. I believe this is highly recommended by Joe Talmadge.

If already convex ,no need to thin out the blade.

but don't worry about thinning it. just sharpen the edge like a v-grind edge, in a few years of sharpening the knife will become much more v-grind like.

If I remember correctly, using a flat stone on a convex edge would hit the rounded "shoulders" of the edge, not the edge itself, and so not sharpen the blade. The convexity would have to be removed for a flat stone to hit the edge.

WhitleyStu-- Nice modification! Glad it works well for you.
Grampa-- I bought a 1X30 belt grinder a few years ago but could never get a good convex edge with it, or by trying several other convex sharpening methods. From the posts I've read, some guys can get a good convex edge and some can't.

thombrogan-- Impressive memory! I am a big fan of Razor Edge hones and their sharpening method, which I use on many of my knives. However, since the big choppers usually take a lot more abuse than smaller knives, before I started removing metal I wanted to be sure a thinner edge would hold up when chopping hard, dead wood. You are correct that the Razor Edge coarse hone removed metal faster than my 1"x30" sander and DMT 120 grit. I like to freehand sharpen my outdoor knives (so I can do it proficiently in the field) and only use the Sharpmaker for kitchen and folding knives.

Andrew Colglazier-- Glad you are getting sharp knives but steeling isn't sharpening. Eventually you will have to sharpen.

 

[Andrew Colglazier]

Andrew Colglazier-- Glad you are getting sharp knives but steeling isn't sharpening. Eventually you will have to sharpen.

Steeling isn't sharpening?

My knives must be dull as toast, then.

Not sure why you think that, but... I can assure you, it really does sharpen!



Andy

 

[Andrew Colglazier]

This is one of my favorite big choppers, an 18" HI Pen Knife. I use it all the time for heavy chopping on our property, clearing brush.

I just use a big butcher's steel on it. I don't let it get tremendously dull, I touch it up regularly. It gets quite sharp.

Andy

 

[Andrew Taylor]

Steeling isn't sharpening?

My knives must be dull as toast, then.

Not sure why you think that, but... I can assure you, it really does sharpen!



Andy

No it doesn't. A steel 'hones' the edge. It makes the edge sharp again, but does not sharpen in the context of grinding. If your knife is blunt, no amount of steeling will give it an edge.

The edge of a sharp blade comes to an infinitessimally thin edge. In use this edge becomes damaged, usually rolled over. The steel takes the rolled over, or deformed edge and puts it back upright in a nice straight line. This is why you can hone a knife using the spine of another knife. You are just re-aligning the edge. I use this technique at work many times if I am not need a steel. I am a chef.

Difficult to explain and very easy to show in real life, but if you look at the edge of a sharp knife, edge on and you can see glints of light, so you are actually 'seeing' the edge, it needs steeling. After that, if you look at the edge, you won't be able to see it because the edge is so thin. If you can see all of the edge and see it as a wide glint of metal, then it needs sharpening with a stone or belt. You can run your finger down the edge to check. This is what I teach my chefs, 'If you can see the edge of a knife, it needs steeling. If you can still see the edge, it needs sharpening'.

 

[Andrew Colglazier]

Dunno, sounds like hair-splitting to me.

If a knife is truly blunt, or dull, it needs to have the edge reformed, and I usually use a belt sander to do that.

If I need a knife sharpened, that is, bring it back to the kind of edge that I need for good cutting or chopping, the steel does a wonderful job.

It is, I think, just a matter of degree.

One method requires the removal of more blade material to reform the bevels and allow and edge to be made.

The other method assumes an edge which simply needs to be made sharper.

Since the OP asked about real world sharpening of large chopping knives, and wants something which is realistic, I suggest a steel.

If you don't allow your chopper to become a shovel, a steel will work wonderfully for you.

Andy

 

[thombrogan]

Mtn Hawk,

There's definitely such a thing as "too thin" on a large chopping knife, but that place is usually thinner than the factory bevel on most pocketknives. Usually (insert cynical laughter here), you shouldn't need a bevel thicker than 0.02" at its shoulders (which, of course, doesn't tell you which degree angle to aim for, but that's trial-and-error anyways). I like even thinner, but that requires either using skills I lack of regrinding a lot. If you have calipers or a micrometer, it should be easy going.

Hoping that's helpful.

 

[Broos]

There's definitely such a thing as "too thin" on a large chopping knife, but that place is usually thinner than the factory bevel on most pocketknives. Usually (insert cynical laughter here), you shouldn't need a bevel thicker than 0.02" at its shoulders (which, of course, doesn't tell you which degree angle to aim for, but that's trial-and-error anyways). I like even thinner, but that requires either using skills I lack of regrinding a lot. If you have calipers or a micrometer, it should be easy going.

I'm with Thom! Thin to win! I say that a lot playing golf, too.

 

[Grampa]

Hi again, Mtn Hawk

You asked about ...

. . . the best sharpening method and edge geometry for big chopping knives.

Big chopping knives are used pretty much the same as an ax or hatchet. A similar grind is best. If you examine a good ax or hatchet, you'll usually find a convex grind. It's used there because it works. Holds a sharp edge, and keeps it through the toughest of work. And a good hatchet can be used a lot like an ulu, to slice potatoes or clean fish!

I'd just as soon not convex sharpen, anyway, as most of my sharpening is done in the wilderness. It's much easier to carry a stone for freehand sharpening than pack the supplies that are needed for convex sharpening or heavy and/or bulky tools and equipment.

Your choice, of course, but a good convex edge need very little maintenance while actually being used. Assuming you've sharpened it before you left the house. I carry a small Falkniven diamond/stone card to touch up any convex edges while camping/backpacking/etc. No bulk, no weight.

Most of the wood I chop (pine and fir in the Western mountains) is dead, dry, and quite hard, so I'm concerned about having enough edge durability that blade chipping, fracturing, rolling, or other damage does not occur, yet I don't want the edge so thick that chopping is not effective. Sometimes one knife is all I take, so I need an edge that is also suitable for more delicate chores such as food preparation and cleaning fish and small game.

Like the convex on a good ax or hatchet, a good convex edge on a chopping knife will clean fish and whittle fuzz sticks. Perhaps not quite as good as a small thin blade, but they'll work just fine. Convex edges are sharp, and with proper steel and heat treat selection, are as tough or tougher than anything else out there. Busse and Falkniven and Bark River don't use convex edges because they are fragile and dull!

I am thinking about thinning the edge out at a fairly low angle, which would remove the convex edge and make it into a V-grind, then putting on a 20-30 degree microbevel. This would add some durability to the edge for chopping but still leave it thin enough for finer cutting.

Be sure to read what thom wrote just above.

Note that a convex edge can be done either thin or thick. Busses tend to be on the thick side. They can be thinned nicely for more delicate work.

I am only interested in advice on what is practical and works best, based on real-world experience.

Wouldn't give you any other kind! :thumbup: My support of convex edges is based on too many decades of actually using blades of all sorts. Actual use has convinced me that convex edges are the strongest, toughest, easiest to maintain edges around.

Sounds like you could use some hand-on help to learn to convex sharpen and maintain a blade. Perhaps someone living near you could help. If you live in the southern California area, please PT me, and we can set something up.

Cheers!

Steve

 

[Andrew Taylor]

Dunno, sounds like hair-splitting to me.

If a knife is truly blunt, or dull, it needs to have the edge reformed, and I usually use a belt sander to do that.

If I need a knife sharpened, that is, bring it back to the kind of edge that I need for good cutting or chopping, the steel does a wonderful job.

It is, I think, just a matter of degree.

One method requires the removal of more blade material to reform the bevels and allow and edge to be made.

The other method assumes an edge which simply needs to be made sharper.

Since the OP asked about real world sharpening of large chopping knives, and wants something which is realistic, I suggest a steel.

If you don't allow your chopper to become a shovel, a steel will work wonderfully for you.

Andy

not really hair splitting. Take your 'truly blunt, dull knife' and try and put an edge on it with a steel. When you run out of energy and time, you can tell me I was right, 'a steel doesn't sharpen, it only re-aligns the edge, hones'. :>)

A steels correct name is a 'honing steel' not a 'sharpening steel'.

Anyway, I agree, get a good edge on the chopper and maintain it with a hone, before the edge goes. A diamond hone by DMT is good, and fast.

 

[Mtn Hawk]

thombrogan-- Thanks for reminding me about measuring the bevel. I have calipers and will do that.

It seems, as you said, that finding a good edge (for whatever reason, or reasons, one wants to use it for) comes down to trial-and-error, thinning it out until problems start occurring, then backing off. I once tested 2 Battle Rats, one with the factory convex edge and one which I'd seriously thinned, using John Juranitch's method. This wasn't a scientific test by any means, but I tried to keep everything equal as I chopped hard, dead, dry wood with each of them.

The difference in chopping with the thinned blade was amazing (although I realize that the factory convex edge could have also been thinned out). I wish I could remember how the thinned BR edge held up (I should have written all that down at the time, as my memory for detail is less than perfect) but as I recall I was very impressed with it, considering the hardness of the wood and the force I put into the chopping strokes (I'm a fairly big man in fairly good shape). I'd probably feel uncomfortable leaving the edge that thin (hence the advice I asked for in this thread), but the result was great!

Thanks. Your posts are always very informative!

Andrew Colglazier-- You are right that steeling can do a wonderful job, but sharpening and steeling are 2 completely different processes, as Andrew Taylor points out. They're further apart than just a matter of degree. Even though steeling makes a knife sharper it's not called "sharpening. As in any field, if you want to communicate with other people in that field you have to use the same terminology, even though some words might have a different meaning than what you learned in the past.

Here's a link to one of the best sharpening articles I've read, by Joe Talmadge, who is also the moderator of this sub-forum. He talks about steeling about 2/3 of the way down.
http://www.knifeart.com/sharfaqbyjoe.html

Grampa-- I've read too many positive things about convex edges and, as you said, too many top knife manufacturers use them, to make me doubt that they are good edges. My problem was that I couldn't convex sharpen. If I had received your gracious invitation a few years ago, I probably would have taken you up on it. Might still, if I get down to S. CA again. Thanks.

I think with beveling, especially putting a secondary bevel on, as Dog of War suggests, I am getting close to a convex edge, although obviously not as smooth, so I don't feel like I'm too far out of the loop. Perhaps in the future if/when time permits I'll give convex sharpening another try.

 

[sketchbag]

With regards to the steel, the type with fine grooves running the length, they do remove metal, but very slowly. If you use it for a while than wipe it with a white cloth you'll see. But to use it on a fully blunt knife would be like sharpening the same knife with a super fine stone, it's just the wrong tool for the job.