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TOPIC: Further on Convex Edges

Further on Convex Edges 2 years 8 months ago #1202

  • leomitch
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In an earlier post I stated that most of my knives had a 22.5(+/-) degree per side bevel with a convex shoulder because I found that edge geometry to be very sturdy yet capable of excellent sharpness.
Not being one to stay with the status quo, I decided to try a more acute angle with the convex shoulder to see if that gave a reliable edge with the kind of keenness we all strive for. I chose an angle of 18 degrees as opposed to 22.5 as my target angle.
I chose three of my knives to experiment with: the Bark River Bravo 1(A2 tool steel) and STS-5 (154 CPM SS blade) both of which have convex blade grinds with extremely delicate, acute edges



and my excellent Helle Temagami with a triple laminate carbon steel blade which has a Scandi grind with a bevelled edge of 17 degrees from the factory.



I used settings of 18-20-22 degrees...the 18 degree angle being the primary edge while the other two were melded together with the first to create the convex shoulder. (See instructions for developing a convex edge on the Wicked Edge web site). Please do not confuse a convex edge with a convex blade grind.
The upshot of this experiment was three knives with final edges of 18 degrees verified with my angle cube (as were all settings throughout) with wonderfully formed convex shoulders. To say that these knives were simply sharp is to make a gross understatement...they were preternaturally sharp. As an old Knife Forum mate used to say, “...so sharp they cut your eyes just looking at them!” Certainly the two Bark River knives that had had the extremely acute convex edges were just as sharp if not sharper, but I believe also stronger so there will be no rolling of the edges as I experienced while making fuzz sticks for a fire with my grandson Owen. Knives like that should never have rolled edges with such a simple task. Similarly the Temagami knife by Helle was super sharp. Time and usage will say whether this experiment produced a useful and sturdier edge or not, but to be sure the experiment was fun. It is my belief that education/learning/experimentation should never stop until you die...it is one of the things that makes living worth while.

Cheers
Leo
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Gibbs rule number 9

Leo James Mitchell
Last Edit: 2 years 8 months ago by leomitch.
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Re: Further on Convex Edges 2 years 8 months ago #1205

  • wickededge
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leomitch wrote:
It is my belief that education/learning/experimentation should never stop until you die...it is one of the things that makes living worth while.

Cheers
Leo

+1 to that Leo.
--Clay Allison
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Re: Further on Convex Edges 2 years 8 months ago #1206

  • glenewertz
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Good report Leo, nice to catch up with you my friend! Hope you are doing well.
I haven't tried convexing yet but so far my Gyutos, (chefs) knives hold up very well with an 11.5 to 12 deg. angle.
Of course my knives don't get the rigors of outdoor use like yours! And I probably get some micro convexing from finishing with the polishing tape mounted to the leather strops.
But I will try it on my Spyderco ZDP189 Delica, which is my EDC, the next time it needs sharpening.


Glen
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Re: Further on Convex Edges 2 years 8 months ago #1207

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Glen my friend! It is good to hear from you and find you over here in Clay's forum. It is not as busy as the Knife Forum, but it is a friendly place.
I agree totally that someone who butchers as a business as you do, certainly can make good use of the extremely acute edges you refer to...my point deals simply with knives used for things like bush-craft, hunting and survival situations.
Let us know how you make out putting a convex edge on your Spydie Delica
Please come back often mate...we are after-all both Leo's astrologically. Keep in touch Glen!

Warm regards
Leo
Never go anywhere without your knife!
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Leo James Mitchell
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Re: Further on Convex Edges 2 years 8 months ago #1218

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Just by the by, my STS-5 from the above post, now sports a handle of Cocobolo wood instead of the original G10 slabs seen in the other shot from an earlier time. IMO there is something so appropriate about Cocobolo wood for things meant for combat use and this knife by Mike Stewart over at Bark River Knife and Tool is definitely a combat or fighting knife.



Leo
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Leo James Mitchell
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Re: Further on Convex Edges 2 years 8 months ago #1219

  • babo
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Very nice Leo; I'm looking at picking up a Bravo I myself. Cocobolo just seems to grow on you doesn't it.


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Re: Further on Convex Edges 2 years 8 months ago #1220

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The razor looks really good with Cocobolo too Scott, I love it! You will be very happy with the Bravo 1...you can now get it in SS steel as well as A2 tool steel and either with a ramp or rampless. Many people don't like the notched ramp, so if you get a chance to hold one before you buy, that would be a good thing.

Cheers
Leo
Never go anywhere without your knife!
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Leo James Mitchell
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Re: Further on Convex Edges 2 years 8 months ago #1304

  • zig
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Leo and Company,
A question on Convex.
My Convex edges have had great results, sharpening them in the style of Clay's video, starting at 17 all the way to ceramic, then jump to 20 just till bur w/ ceramics.
Now the guessing part ... stepping down to 19 with ceramics with about 10 light strokes per side of ceramics, not pushing a bur, and checking with glass to see an angle has been made.
Repeat at 18.
Then strop from 14 paste at 17 degrees to .5 micron paste.

All seems well ... but get the feeling that the 19 and 18 degree angles are in a limbo as its a guesstimate of sorts as they never go to bur.
Am having a problem with a VG-10 Endura, as the edge gets paper slicing sharp but never really folded mag paper sharp if you know what I mean. A bit toothy. It causes me to reset to the 20 and strop that for a bit trying to get it to that scary sharp point, just a polish at the final edge, but still a bit toothy.

Am wondering if anyone does convex in steps from lowest to highest?
Say start at 17 to bur and highest stone, say ceramic.
Then ceramic at 18 to a light bur, then 19, then 20.
I'm trying to imagine if that would define the in between angles more accurately than a guess, and maybe having the final pass be at 20 instead of the second pass, maybe have the 20 degree final be more defined.
Then drop back and strop from 17.

Any thoughts?
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Last Edit: 2 years 8 months ago by zig.
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Re: Further on Convex Edges 2 years 7 months ago #1529

  • mark76
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Good question, I wondered exactly the same (if I understand you correctly).

Having sharpened a couple of knives I feel ready now to do a convex edge. My Fallkniven A1 has to be in for it. (Though I am not sure it is the best candidate for that: the entire blade has a convex form, rather than just the edge.)

What I understand is that you propose to sharpen the knife to a burr at 17*, then sharpen it to a light burr again at 18*, to a light burr again at 19* and then to a light burr again at 20*. You only use the ceramic stones for a light burr. Finally you do a strop at 17*.

I think that in theory this should work fine. I just haven't tried it yet.

If anyone has, or has a different view on the theory, I'd be interested to know.
Last Edit: 2 years 7 months ago by mark76.
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Re: Further on Convex Edges 2 years 7 months ago #1530

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Thanks for the reply Mark!

I usually do all my convex from narrow angle first, then to wide, then down and strop.

I have a gut that the in between angles are more or less guesses, know what I mean, as you can't take them to bur.

I'm imagining that by burring very lightly each step say from 17 through 20, the biggest factor would be the height of the edge .. I'm guessing it would be lower, but by how big of a factor?

And, would it make for a stronger rounder shouldered blade, but duller.

Perhaps Leo or Clay or anyone has tried this and has thoughts.
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Last Edit: 2 years 7 months ago by zig.
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