help with cheap, soft, thin steel please

Magnaminous_G

Magnaminous_G

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Jul 13, 2011
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I got some ultra cheapo, super-thin, Japanese-style knives to sharpen. No name brands and mystery steel. Every time I try to sharpen them, they develop chips along the apex. When I clean the chips out with a coarse stone and try to move to medium... new chips. When I raise the angle and finally get them chip-free, I notice something that I've noticed sharpening SAKs before: the edge looks clean and feels clean to the touch, but it doesn't slice newsprint cleanly. It acts like there's tiny chips or burr left on the apex. It catches the paper pretty rough at the slightest turn of angle and only slices somewhat cleanly if guided in one even direction. Stropping doesn't really help. I suspect it ultimately has something to do with the steel being so soft, and I'd like some tips on dealing with this problem. I don't encounter it every day, but I see it every once in a while and still haven't found the solution. I speculate that my best bet is to stop fairly coarse, but I'm at a loss as far as which grit/stone... or what finishing steps. I speculate a combo India stone might be a good idea.

Any ideas and suggestions on stones and grit progression, finishing steps? I'm inclined to tell folks to throw these POS's away and get a real knife, but there's got to be a way to sharpen them to some degree of satisfaction. Advice needed.

Thanks,

Mag
 
We sharpen the softer steels on a belt grinder which makes it easy but there are some knives that are too crappy to take a quality edge. When these knives come in we let the customer know that it simply might not get sharp.

Not much you can do but give it your best shot. Probably a good time for that India stone....
 
Use another knife or the faces of the knife you're working on, and whip up some mud with your 1k stone. Gently wipe it up/lift it off with a sheet of paper and wrap this around a dry or relatively dry stone (your 6k). Use this for a strop, go easy.

HH
 
I'm struggling to understand why a soft steel would chip and why it would not chip under a coarse stone but does under a medium stone.

If the steel is really soft and thin, I'd think you could clean up the edge fast with fine diamond stones and refine it from there with regular, high-grit stones under under extra light pressure.
 
The 'chips' in soft steel aren't actually chips (fractured metal coming off), but just deep impact deformations in the steel. 'Chipping' implies fracture, which implies brittleness, and you can't really 'fracture' something that soft. But, it's real easy to put deep dents/gouges in it which, to the naked eye/touch, closely resemble a chip. I tend to think of it in terms of striking a stick of butter, wax or something else of similar plasticity with the edge of a knife. It'll leave deep damage in the soft material, but it doesn't actually cause material to fracture off (chip), as would be the case with much harder steel or glass, etc.

With real soft steels, I always substitute a finer grit for initial re-bevelling or heavy grinding. I've never used anything coarser than a medium grit to start, and often start with fine, when using diamond hones. The only way I've ever been able to keep a reasonably durable edge on soft steels is to leave it somewhat toothier than I'd do with harder steels, and always, always keep pressure feather-light. They are very prone to rounding off, when that soft, and just one or two errant passes off-angle will erase any crisp apex that might've been there before. Doing it at too-fine a grit will quickly round and over-polish the apex, erasing any remnants of 'bite' right out of it.

HH's suggestion for stropping on a hard stone w/paper and some grit makes a lot of sense to me. I haven't duplicated his method exactly, but have found that stropping on some coarse/medium-grit sandpaper over a hard backing (glass, for me) works very, very well on 'softer' steels. Recently, I put a real wicked-slicing edge on an older Japanese-made paring knife (no-name stainless), using a stropping stroke on a couple of emery/nail files (black & pink, of the variety found at the drug store), which essentially replicates using the sandpaper. I usually follow up with stropping on the rough side of my leather belt, to clean up any burrs or other edge debris, if necessary. Sometimes, even compound on leather is overkill with soft-steel edges, and might tend to over-polish as well.


David
 
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I find that most knives with inferior, for lack of a better word, steels often crumble while sharpening. Always an oh c**p moment. As stated above you just have to go slow and easy on higher grit stones to get an decent edge. I stop at 1200 on less on those. Not much else one can do except make more work for yourself.
 
Yeah, finer grits are the way to go.
I think that if you manage to get the knife sharp, it won't stay that way very long.
 
There comes a point where it's just plain counter-productive to try to polish a turd.
 
One thing I think is often overlooked with steels like this, is that due to being cheap the manufacture of the knife isn't controled as closely as higher end stuff. So, if this steel (or this particular knife) was over heated during HT it could have lead to increased grain growth. Also, being cheap stainless, it likely has a good amount of Vanadium, which produces very large carbides. So having a weak structure (soft steel with poor grain) and large carbides, you can only get so fine of an edge. As you start to refine it, the carbides are being ripped out, falling out and grain boundaries are failing. This leads to a toothy edge, likely only able to perform at grits of 1K and under.

Increase the edge angle to 35* or more, and leave it at a lower grit. It will cut like crazy through food, cardboard, and rope, but like James said, when your done polishing a turd, it is still a piece of sh!t.


-X
 
fast14riot said:
One thing I think is often overlooked with steels like this, is that due to being cheap the manufacture of the knife isn't controled as closely as higher end stuff. So, if this steel (or this particular knife) was over heated during HT it could have lead to increased grain growth. Also, being cheap stainless, it likely has a good amount of Vanadium, which produces very large carbides. So having a weak structure (soft steel with poor grain) and large carbides, you can only get so fine of an edge. As you start to refine it, the carbides are being ripped out, falling out and grain boundaries are failing. This leads to a toothy edge, likely only able to perform at grits of 1K and under.

Increase the edge angle to 35* or more, and leave it at a lower grit. It will cut like crazy through food, cardboard, and rope, but like James said, when your done polishing a turd, it is still a piece of sh!t.


-X
Click to expand...

I suspect large(ish) grain size was an issue with the older no-name stainless paring knife I'd mentioned earlier. It just won't hold a very fine edge for long, and requires frequent touching up. It does seem as if the 'teeth', when they get too refined, just crumble away from the apex or otherwise just get scrubbed off. So, at too-high finish (maybe 600 grit or higher, FEPA-P), a lot of it's 'bite' is lost very, very quickly with minor cutting. In spite of the lack of durability, it still cuts much better at lower grits, and thinning the geometry has also helped in regards to slicing. I think the sweet spot for it is in the neighborhood of 320 grit or so. As a 'light duty' knife for slicing fruits & veggies, it's very easy to get along with.


David
 
Tried a couple things. Here's what worked:

Regrind new bevel with Naniwa Omura and DEBURR on that stone
stonework with Arashiyama 1k, careful deburr work with same stone
very light strop with green compound on leather

Got a good, stable edge with no chips at approximately 20 degrees per side (confirmed with CATRA laser goniometer). Thanks for all the advice and suggestions. I know I didn't take all of them, but HH's advice to rely on the grit of the 1k really helped a lot. A few people warned about overpolishing, which was good advice, as well. The final stropping with green compound was *very* minimal. If I had done 10 more passes on each side, it might have been too much.

EDIT: Actually, I'll make a vid of doing another one of this guy's crap knives to show the process.
 
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