Curved blade sharpening issues

M

Musicman88

Joined
Sep 25, 2020
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Hi to all. I purchased a bastinelli diagnostic (karambit style neck knife) a while back and the edge got rather dull after using it for a good while. It used to cut paper like butter and sliced through pretty much anything in front of it. I tried sharpening it with the diamond rod on a lansky blade mechanic and now the edge is not performing well. I'm in desperate need for help as it is one of my favorite knives and it just wont cut as well as it used to. i sharpened my fox 599 on the blade mechanic and it cuts AMAZINGLY well. Havent had the same luck with the diagnostic. As the knife only has a edge bevel on one side its extra tough to get it back to where it was. Any suggestions would be greatly appreciated, however, I live in Cyprus and although Bastien (the maker) did say he would sharpen it for free, it would be a major cost and hassle to send the knife to Florida to get it sharpened. We literally have very few knife enthusiasts here (if any) and just wanted to try and get your opinions on the matter and if possible solve my edge problem.

Some things to consider:

1- the knife will cut things like cloth leather fruits and veggies but WILL ABSOLUTELY NOT cut paper (tried a few types)
2- I can definitely feel a bite when i run it on my thum
3- it will bite and scratch off material on my nail but only if i run it from the opposite side of the edge bevel (which is weird)
4 - I have tried stropping it on a belt but maybe im doing it wrong (as the edge is only on one side i strop it that side down, this maybe wrong)

Thank you all in advance!
 
Sounds like you probably developed a significant burr. This is easy to do if you’re sharpening mostly/entirely on one side of the edge. Look up what burrs are, how they form, and how to control them and I bet you’ll be good.
 
just a quick comment. concave blade shapes are challenging to sharpen because the blade can't be sharpened on a flat benchstone. scythes are even 3D-concave, argh!
 
Some inexpensive diamond rod-type sharpeners can be too coarse and overly aggressive on mainstream stainless steels, leaving the edge ragged and burred. The steel in your blade is N690 I believe, similar to VG-10. If you have access to a medium/fine ceramic sharpener (maybe your Lansky BladeMedic has one?), some follow-up refinement on that should help.
 
scdub said:
Sounds like you probably developed a significant burr. This is easy to do if you’re sharpening mostly/entirely on one side of the edge. Look up what burrs are, how they form, and how to control them and I bet you’ll be good.
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Thanks for this, I went ahead and did some research and applied some methods that said might help and it is indeed a little better, but its not as sharp as it was. Can feel bite on the thumb and definitely bites the nail (in both directions now evenly) but its not there yet, it definitely has issues with paper still.
 
kreisler said:
just a quick comment. concave blade shapes are challenging to sharpen because the blade can't be sharpened on a flat benchstone. scythes are even 3D-concave, argh!
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i have quite a few knives and im no sharpening expert (obviously) but this is definitely the hardest blade i tried to sharpen, couldnt imagine how hard it would be to sharpen a scythe!
 
Obsessed with Edges said:
Some inexpensive diamond rod-type sharpeners can be too coarse and overly aggressive on mainstream stainless steels, leaving the edge ragged and burred. The steel in your blade is N690 I believe, similar to VG-10. If you have access to a medium/fine ceramic sharpener (maybe your Lansky BladeMedic has one?), some follow-up refinement on that should help.
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Yep, the blade is made out of n690c. The blade medic does have a ceramic strip (triangular) which i often use to sharpen other blades but when i tried the ceramic on the diagnostic it didnt feel like it was doing much if not anything at all. If I went ahead, manically, passing through on the ceramic, do you think i might make another one sided burr? Still trying to figure it out! Also, Im really trying to not eat through the PVD black coat, which actually is undamaged still even after these sharpening adventures.
 
Musicman88 said:
and applied some methods that said
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deburring and sharpening might not be an art (i could disagree) but it is a craft. assuming that you have apexed the edge and you deburred the edge but the edge is still not performing as wished, then it's because it is not deburred properly yet.

that is the challenge i was talking about.
 
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Musicman88 said:
Yep, the blade is made out of n690c. The blade medic does have a ceramic strip (triangular) which i often use to sharpen other blades but when i tried the ceramic on the diagnostic it didnt feel like it was doing much if not anything at all. If I went ahead, manically, passing through on the ceramic, do you think i might make another one sided burr? Still trying to figure it out! Also, Im really trying to not eat through the PVD black coat, which actually is undamaged still even after these sharpening adventures.
Click to expand...

I was looking at an online image of the BladeMedic, and I did notice the triangular ceramic is included on that.

I mentioned the overly-aggressive nature of some diamond rods, in part because I recently purchased one of that type (a Smith's product) just to see what it was capable of. I ran into similar issues on a blade of VG-10 (Spyderco), using that device to touch up the edge. Edge was left pretty rough and I had to follow up with some very, very light passes on ceramic (Spyderco medium and/or fine Sharpmaker rods) to get the edge back to paper-slicing relatively well. And in fact, one of the ceramics I tried was a triangular hone designed for Lansky's guided sharpener. So, being that all of this occurred in the last few days, much of this is still fresh in my mind.

The main key is making sure that all of the work is done with a light touch, with either the diamond or ceramic. That's especially important with diamond rods of any kind, and more so if the rod is pretty coarse, like many of the pocket/portable devices seem to be. Ideally, I'd prefer these to be no more coarse than about 1200-grit for finishing's sake (compare to DMT's EF diamond, for example). But most of them are probably in the 400-600 range, and some perform much coarser than that, in my experience with them.
 
kreisler said:
deburring and sharpening might not be an art (i could disagree) but it is a craft. assuming that you have apexed the edge and you deburred the edge but the edge is still not performing as wished, then it's because it is deburred properly yet.

that is the challenge i was talking about.
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I would definitely call it an art. Shaping material in certain ways is an art in my books :) But you're right it probably needs some more work. I'm definitely on the right track though, its starting to be able to shave the hairs on the back of my palm and cut straight through paper, not 100% there yet though! (day 3 of getting it to this point :P)
 
Obsessed with Edges said:
I was looking at an online image of the BladeMedic, and I did notice the triangular ceramic is included on that.

I mentioned the overly-aggressive nature of some diamond rods, in part because I recently purchased one of that type (a Smith's product) just to see what it was capable of. I ran into similar issues on a blade of VG-10 (Spyderco), using that device to touch up the edge. Edge was left pretty rough and I had to follow up with some very, very light passes on ceramic (Spyderco medium and/or fine Sharpmaker rods) to get the edge back to paper-slicing relatively well. And in fact, one of the ceramics I tried was a triangular hone designed for Lansky's guided sharpener. So, being that all of this occurred in the last few days, much of this is still fresh in my mind.

The main key is making sure that all of the work is done with a light touch, with either the diamond or ceramic. That's especially important with diamond rods of any kind, and more so if the rod is pretty coarse, like many of the pocket/portable devices seem to be. Ideally, I'd prefer these to be no more coarse than about 1200-grit for finishing's sake (compare to DMT's EF diamond, for example). But most of them are probably in the 400-600 range, and some perform much coarser than that, in my experience with them.
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I might have removed most of the diamond coating off the rod sharpening some old japanese kitchen knives that were almost totally dull heheh. I also (during this time) went ahead trying to deburr even more and I used your suggestion with the ceramic and it CAN shave hairs of my hand and WILL cut straight through paper with much more ease. Not like my other knives though and certainly not like it originally did. Maybe if I continue with the ceramic it will get better and better?
 
Musicman88 said:
I might have removed most of the diamond coating off the rod sharpening some old japanese kitchen knives that were almost totally dull heheh. I also (during this time) went ahead trying to deburr even more and I used your suggestion with the ceramic and it CAN shave hairs of my hand and WILL cut straight through paper with much more ease. Not like my other knives though and certainly not like it originally did. Maybe if I continue with the ceramic it will get better and better?
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It could continue to improve. Part of the outcome will be determined by the shape of the edge geometry itself, after it was worked with the diamond hone earlier. But with a light touch, the ceramic should help clean up the apex and get it back to something more stable and predictable, in paper-slicing and everything else it's expected to do.
 
Along the same lines as FortyTwoBlades suggested, I'd also thought of a dowel or piece of pipe (like PVC) used with some wet/dry sandpaper. All the better, if the paper is glued or firmly attached to the dowel or pipe. Use it edge-trailing, as with stropping. At coarser grit like 220 or so, it could be used for shaping the bevel geometry. And at medium-to-fine grit, like 400-1000+, it can be used for refining & polish. Should work OK for that particular steel, if such materials are available & at-hand, where you are.
 
Obsessed with Edges said:
Along the same lines as FortyTwoBlades suggested, I'd also thought of a dowel or piece of pipe (like PVC) used with some wet/dry sandpaper. All the better, if the paper is glued or firmly attached to the dowel or pipe. Use it edge-trailing, as with stropping. At coarser grit like 220 or so, it could be used for shaping the bevel geometry. And at medium-to-fine grit, like 400-1000+, it can be used for refining & polish. Should work OK for that particular steel, if such materials are available & at-hand, where you are.
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Will definitely give it a go with the finer grit tomorrow, I was refinishing my guitar recently which required me to get a lot of different grit sandpaper. I could probably find a pipe or something cylindrical that i could wrap and glue sandpaper on. I will definitely experiment tomorrow.
 
FortyTwoBlades said:
If it's thin enough to fit inside the curve, yes, but most karambits have a pretty tight curve so you'd be looking more for something between finger and pencil thickness.
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Hey just wanted to give an update on my diagnostic. So today i went ahead and worked on it more with the diamond rod, then i worked on it some more with the ceramic and then i stropped it using a wooden tribal wind instrument that i happen to have laying around (cylindrical a little bit larger than a pencil), stropping very lightly and holy hell its gotten seriously sharp!! Many thanks guys for the support, cant believe this was resolved within a day after reaching out here :)
 
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