convexing bk2

I convexed mine using the videos on knivesshipfree. Any of the convexing tutorials will work, though.


If I'm not supposed to directly link to the site please remove the link.
 
Exactly the same process as convexing anything else, from a knife blade to a piece of wood or plastic---grind a curve. This can be helped out with a slack belt, but can be done on a flat platen by making several, small flat bevels at graduated angles and then rounding off their shoulders to make one smooth transition across all the planes. For that matter, you can do the same thing and convex a blade with any stone or metal sharpener, though your progress will be much slower, of course. Wet/dry sandpaper on a mousepad, sanding block, or thick piece of leather is a tried-and-true technique too, though it also requires a good bit of time.

You have to decide just "how convex" you want things to be---meaning do you want a uniform, continuous curve throughout the whole width of the blade resulting in a very thin edge, or an gradual one up top with more extreme curvature down near the edge which will more closely approximate the cutting characteristics and edge strength of the factory grind?

The two most important things are to not get in a hurry, and to protect your heat treat. The latter is only an issue if you are using power tools, of course, but a very important one. All that follows assumes that you're going the power tool route:

I do not let a belt linger on any part of an already heat treated blade for longer than a second (or one and a half) at a time--meaning that I'm pulling the blade horizontally across the belt at a rate where the width of the belt is the distance the blade moves across in 1 to 1.5 seconds. So, on a 1" belt, it would take me three to five seconds to pull the entire length of a BK2's blade across the belt. Obviously, I'm rocking faster on a 2" belt than a 1", but that's okay as just as much steel is being removed. Anyway, I usually do a few (3 to 5) passes like this and then dunk the blade in a room temperature bucket of water for a few seconds, dry it off, and go again. The thinner the knife (and the thinner your edge gets as you go) the more careful you need to be about over-heating it. Use new belts, and when one obviously starts slowing down in its cutting, chuck it and move on to another, as belts just run hotter and hotter the duller they get.

My last advice to you is what I always tell people---don't perform your first mods on a knife you like. I learned grinding on a sack full of $5 chinese machetes that I bought from a hardware store. I say "learned" though I'm certainly not the equal of most of the honest-to-goodness knifemakers on these boards. Still, I'm a hell of a lot better than I was, way back when. Now, if you want to practice on something that's closer in size and thickness to your Becker, you can buy something like this for example:
http://www.knifecenter.com/kc_new/store_detail.html?s=UC947CSNB

There's three knives in that pack, working out to about $10 a piece once you've shipped 'em. Of course, they'd be changing a hollow to convex versus flat to convex, so you also might look at something like this as being--in terms a grinds--a closer approximation to what you intend to do.

http://www.knifecenter.com/kc_new/store_detail.html?s=CN23243HC

Best of luck, don't get discouraged by inevitable screwups, DO remember that almost any screwup is correctable, and protect that heat treat! :D
 
t1mpani...


thanks for the write up.. I thought I was well versed on my sander but you've made me think alot.. although the blade itself may not get that hot its the actual edge on the knife that does.. I move much slower then you said, and I rarely ever use water unless I'm re-profiling, I hope I haven't damaged the heat treat to some of the knives I've done..

I'll tell you one thing, I bought the cheap CS Khukri for $14 out of the box in use it had some small chips in blade from hitting the ground (rocks, dirt etc)..

I convexed it, and its my goto camp knife most of the time, I can't beat another chip in it and I've tried now for about a year..
 
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garnto, I checked out the link.. that's actually a great deal on the strop with compounds if you ask me..

I make my own and buy scrap leather pieces by the bag at a local farm shop for $5.. I can make like 5 2 sided strops but then my green compound is like $10..

you better jump on that..
 
TheLastDaze said:
t1mpani...
thanks for the write up..
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You're entirely welcome, glad it was of some use to you.

To the OP:

By the way, you may well have been intending to do so already, but be sure to strip the coating off first before you being to convex---that stuff will clog up a lot of paper, and there's no point wasting it when some chemical stripper will pull it off in a hurry.
 
To add:
Also, consider picking up some 100 grit paper instead of 200 as a starting point. You're going to be removing a LOT of steel and the 100 grit really helps speed things up. I regularly convex 18" long, 1/2" thick kukris and starting with 100 instead of 220 grit has cut down my time by probably a third.

Also, remember that all your work should be done with your starting grit - all the higher grits are purely for refining the edge you establish with your coarsest paper. This means you should never move on to higher grits until you can definitively feel a raised bur all along the edge and that the geometry is how you want it. It also means you should be buying about 3-4 times as much of your coarsest as your higher grits. I personally buy 3 packs of 100, and 1 pack each of 220,400,800,1000 - from experience, this ratio seems to run out pretty close to the same time.

Best of luck and if you have any further questions, just ask away! :)
 
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With the BK-2, I would imagine you almost have to lift up to alleviate some of its weight to avoid rounding the edge, correct?
 
willworship said:
With the BK-2, I would imagine you almost have to lift up to alleviate some of its weight to avoid rounding the edge, correct?
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Well if that were the case, I certainly would have a much harder time putting a shaving sharp convex edge on my 2.5lb kukris. I already get enough of a workout sharpening these up as is :p
That said, it's difficult to overdo the edge rounding without using a downy pillow instead of a mousepad or using an insanely obtuse angle. I actually tend to ADD a little pressure (though I sharpen flat on the bevel to make for a zero-angle convex grind)
 
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Maybe I was going too steep before. All I know is that I stink at convexing. Beveled edges come so much easier for me. I'll take another stab at it.
 
willworship said:
Maybe I was going too steep before. All I know is that I stink at convexing. Beveled edges come so much easier for me. I'll take another stab at it.
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Try going almost flat with the primary bevel then just raising it up a very small bit... the flex of the mousepad will give you your angle. Also, are you making sure that you've formed a noticeable bur at your coarsest grit before moving on to higher grits? I think this is probably the most common issue I've seen people run into... you're completely re-profiling the blade and if a noticeable bur hasn't been formed, your old V-grind is still partially there and the two sides aren't completely meeting at a point. As I said before, the majority of your work is done with your lowest grit - higher ones are simply for refining the edge to the desired polish.
 
Lots of Sand paper starting for 300 to 1800 and polishing white compound.
100_0210.jpg
 
I find that with heavier knives I do lighten up. Less pressure on both mousepad, and when I use the strop.

Some of my knives are 2.5 lbs.

I also, on most of them, do a steeper angle. Flat grind to convex edge, so I am sharpening at a higher angle, and have to be more careful of edge wrap.

I will be a bit more firm when I put the sandpaper on leather backing.
 
killa_concept said:
No problem mate - let me know how it goes! :thumbup:
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Thank you for the help. I was successful at getting a hair-popping convex on my BK-2 yesterday!

The video link above was also very helpful in pointing out the difference between older and newer mousepads. I was using a newer one that didn't have much give to it, and therefore didn't work for convexing. The older ones are softer and work much better.

Switched mousepads, started at a much lower grit and stayed there until the burr formed, and voila!

Thanks again. I don't feel so ignorant about convexing anymore.
 
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Go look at virtuovice on you tube. He is a master at convexing! He does all of his beckers!!!!
 
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