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Best edge for a beater knife?

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Michi

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I've just been given a knife by a friend to "resharpen". Its condition is such that, by the time I have new bevels established, the knife will be 0.5 mm narrower :( It's unbelievable how people get their knives into such a state and then manage to cut with them regardless, sometimes for years…

Anyway, I've sharpened a whole bunch of other knives for that person (also in a very sorry state), and those knives are nice and sharp again. I recommended to have one knife as a beater knife that is used for the rough stuff. That way, the other knives stay in good condition and the beater knife takes all the abuse. The knife I'm about to start on is going to be the beater.

So, what's the best way to create an edge that will hold up to abuse as much as possible? The knife is going to be used a lot for cutting frozen fruit. Suggestions for angle? I'm thinking 20º, maybe more? Micro-bevel? If so, what angle for that? One side or both sides?

For what it's worth, the knife was originally purchased at Ikea about 30 years ago. Some kind of generic stainless steel; it says "Molybdenum/Vanadium, Made in Japan" on the blade.
 
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aszma

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I mean if the primary use is frozen fruit and he bought it from ikea wouldnt it just be a good idea to save everyone time and buy a new 5 dollar knife from ikea instead of trynna fix a 30 year old beaten knife?
 

Michi

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wouldnt it just be a good idea to save everyone time and buy a new 5 dollar knife from ikea instead of trynna fix a 30 year old beaten knife?
That’s exactly what I suggested, too. But it’s an emotional thing; there are memories attached to that knife…
 

Midsummer

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22 degrees is standard for good german/ french /english steel. My bench chisels go at 35 degrees. I think I would aim for a bench chisel grind.
 

ian

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How does that work? I honestly have no idea.
Think he’s just saying make it a big angle, like 35 degrees. Doubt he’s suggesting you transform it into a single bevel.

I’d agree with a fat bevel. Just do a 30 degree angle each side and be done with it.
 

Midsummer

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How does that work? I honestly have no idea.
I am far from the best sharpener and actually a double bevel knife sharpened to 15 degrees a side would have a 30 degree inclusive bevel. My chisels are single bevel. But I guess my point is that when working with delicate woods you can have a smaller bevel and it is easier to work. With harder woods and more abuse you want a heftier bevel.

So I would angle the spine to the plane of the sharpening surface to about 30-35 degrees (probably 30 as it a third of 90 degrees) and grind on a 500(or longer on a 1000). Once apexed, do the same on the other. It can be surprisingly sharp. It just does not enter food easily. Does that make sense?
 

kayman67

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Convex, high angle, 25-30°. If the overall geometry is suited for such construction. In theory this should be able to survive hammering bones and cut decently enough.
 

M1k3

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20-25° or so. Around 500-1k grit finish.

A meat cleaver is nice for frozen stuff. Kiwi makes an inexpensive, durable one.
 

daveb

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Fat angle, coarse stone.

Having done a few years in Uncle Sam's Navy I liken the knife blade to the bow of a ship. On a ship that's designed to cut through the water with ease, the bow will be narrow and longish. You're trying to make an icebreaker. Blunt short bow for solid strength. No reason to polish the edge.
 

Michi

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Thanks for all the tips, I much appreciate it!

I think I'll try with 25-30 degrees and convex the bevels a bit. It should still be sharp, and have a bit more meat behind the edge that way.
 

Benuser

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I'd start with automotive sandpaper, P240, with a rubber or soft wooden backing, edge trailing only to avoid overgrinding. Gives a nice convex bevel in line with the face. From there on cleaning up by edge trailing 'stropping' and deburring on a medium stone. I go directly to a Chosera 800. If it is the equivalent of Krupp's 4116 you may stop, otherwise just light further deburring on a 2k or what you have.
 

vicv

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I agree with @Benuser, that is how I would do it if I didn't have my belt grinder. for those type of knives I do use lion and I basically lay the knife flat on the slack portion of the belt with moderate pressure at the edge. This gives a low angle but high roundedness convex edge which is very sharp and holds up very well to the type of use that you are implying this knife will see. The same type of edge can still be made with sandpaper with a soft backing it will just take much much longer
 

Michi

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Thanks @Benuser and @vicv. I can see how the soft-backing sandpaper idea will help to convex the bevels. I was thinking of using my 320 Cerax and Carter's rocking technique to make a convex bevel. But the sandpaper thing might actually be easier. I have some firm polyurethane mats around that probably would be just right for this.

I'll tackle this over the weekend. Plenty of P240 sandpaper around here anyway :)
 
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kayman67

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It's perfectly doable with stones, but if you never did it before, takes a bit. So use what feels easier.
 

dough

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I been down this road too many times “helping” friends save whatever knife and I like a clamshell shaped edge.
I see that’s what is currently being discussed. It’s called hamaguri in Japanese but that and thining the blade road/refinishing the knife is usually my move. Sure it’s too much work but I only do it for people that love their things.
 

Michi

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So, I had a go at this thing. And, man, it's killing me…

The knife had really deep chips and was in terrible shape (including about 5 mm missing at the tip because someone dropped it on the floor years ago). So, I took my Cerax 320 and went to work at 30º, figuring the first order of the day would be to establish new bevels before I worry about anything else.

So, I sharpen away and, man, it's painful. Multiple passes (as in ten or more each side) before I finally got all the chips out and the edge was clean. I checked with a loupe, and I got very nice clean bevels established, maybe just under 1 mm in width, without any faceting and a very even scratch pattern.

So, I figured I'll keep going until I raise a burr. Now, normally, with the Cerax 320, I get a monster burr in one or two passes, even with German stainless steel, such as on a Wüsthof or Victorinox. With this thing, no joy. I kept trying and trying. I could see that steel was coming off from the swarf on the stone, but no burr. Multiple attempts over maybe two hours, going really hard on one side, then really hard on the other side, no luck. Going lightly, no luck. Alternating sides, no luck. I cannot feel a burr, no matter what I do.

In the end, I gave up in disgust, changed to deburring strokes (edge leading) with light pressure, and tried the knife. It cut like crap. Tried again after some more edge trailing strokes. Same result.

In the end, I figured "OK, let's see what happens if I hone with a diamond steel." I got something resembling a toothy edge that sort of cut, but not well. Back to the drawing board…

Trying with my Cerax 1000 this time. Definitely removing metal, lots of swarf on the stone. Looking at the bevels with a 20x loupe, I can see that the bevels are perfect, very even scratch pattern. But no burr. Try to cut something again, and it's not much better.

OK, let's see what happens with green compound on the suede side of leather. Only marginal improvement.

In the end, I used the diamond hone again, followed by a normal steel hone, and managed to get something that cuts, but poorly. It'll cut paper OK (but loudly) along the grain, and reluctantly (and noisily) across the grain.

I don't know what is happening here, but I'm fairly sure it's not me. I just sharpened three knives I received from the same person, in equally terrible shape (two Victorinox and one Elite). Those are made from X50CrMo14, and I had no problems at all. Razor-sharp once I was done.

But this thing left me defeated :(

IMG_3536.jpg
 

KingShapton

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Sounds like wasting your time. Some cheap knives are crap and stay crap, no matter what you do
 

Michi

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Sounds like wasting your time. Some cheap knives are crap and stay crap, no matter what you do
Not the answer I wanted to hear, but I suspect you are right.

I was dreaming of returning that knife to razor sharpness. Now I have to deal with all my shattered illusions instead. It will take weeks… ;)
 

Midsummer

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For cutting frozen food, it seems perfect. I have a 45 year old Henkle stainless slicer that I can not get a burr to form. I keep it to remind me of my limits.

Really nice of you to help your friends. They will be pleased. If they are anything like the people I sharpen for, they will be using the dullest knife the most. Folks seem to be afraid of the sharp knife.
 

madelinez

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I experienced something similar recently with a Chinese clone of a Wusthof, I just couldn't make it sharp. I spent a couple of weeks trying but barely got it past tearing paper.
 

KingShapton

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Not the answer I wanted to hear, but I suspect you are right.

I was dreaming of returning that knife to razor sharpness. Now I have to deal with all my shattered illusions instead. It will take weeks… ;)
I know very well how something like that can get frustrating.

I myself have spent countless hours in vain repairing and sharpening cheap or very cheap knives from friends and my mother-in-law.

In the end, I had to see with some knives that I wasted my time. It was even more difficult to explain to the owners why it cannot be sharpened and why it is not worth it.

I have learned from this before I promise to sharpen his knife, I want to know what it is and prefer to see it beforehand.

So I avoid disappointment and frustration on both sides.
 

Michi

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I have learned from this before I promise to sharpen his knife, I want to know what it is and prefer to see it beforehand.
Smart move!

My ego just took a big dent. I thought that I could sharpen anything with enough determination and patience. Not so…

At least I can feel good about it in the sense that I think I can safely blame the steel. This is the first time after probably 200 or so sharpening sessions that I didn't get something really sharp.

I don't know what steel they used for that thing. It's quite bendy for its thickness, much more so than a Victorinox, which has a blade of about the same thickness. They probably melted down a bunch of recycled fruit tins or some such…
 

kayman67

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Usually I manage to get knives like this sharp, using coarse diamond plates or SiC stones. If you have any, give them a try.

Sharp doesn't guarantee retention for that usage scenario, though. I would also test the edge a bit. See just how soft the alloys is.

If you get these from a couple of known low HRC knives while hitting your edge, things won't be pretty.

Screenshot_20200314-120930_Gallery.jpg
 

Michi

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If you get these from a couple of known low HRC knives while hitting your edge, things won't be pretty.
Ouch, that looks terrible!

Thanks for the tip on the SiC stones. But I don't think I'll go and buy an $80 stone in order to try and rescue a garbage knife that is worth $10, if that.

I think I'm done with that knife. It cuts passably well–I just cooked dinner with it, going through some considerably traumatic moments—and I've decided that "you thing, I'm done with you!"

Enough is enough.
 
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vicv

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Good idea it is time to give up. One day you should get yourself a belt grinder just for this type of work. They are very handy
 

ACHiPo

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Not the answer I wanted to hear, but I suspect you are right.

I was dreaming of returning that knife to razor sharpness. Now I have to deal with all my shattered illusions instead. It will take weeks… ;)
Maybe it’s time for you to pick up a belt grinder?
 
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