Steel too hard to effectively sharpen?

Michael Minto

Well-Known Member
#1
On a couple of occasions I have made a blade that was VERY difficult to put a bevel on. I would keep trying to grind in an edge bevel on my belt sander (using a jig for consistency), but alas, would only grind away more and more steel, without getting the knife sharp (one was D2, the others, 440C). I lost a couple of blades to this. I'm thinking they were about Rc60/61 - coulda been higher, don't have a tester). Has this happened to anyone? Got a fix? Can bevel angle (too high/too low) be part of the issue? Thanks for any useful info. Mike
 
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KenH

Well-Known Member
#2
Most of the knives on here are in the 60+ Rc hardness range with no real problems in sharpening due to "steel too hard". It would have to be north of 65 Rc before the steel hardness would be a factor. I would suspect sharpening technique more than hardness of steel.

What grit belt are you using? What type of grinder? How fast are you running the belt? Just a few of the things to consider.
 
#3
I made a few test knives months ago using an older process where you clay the spine of your blades to keep them softer then harden the edge steel only. The difference here is that you do no further heat treating. In other words, I left the edge at full hardness (1084) with no tempering. The knife would still not snap under usage because the spine is "soft". I was not happy with the results because once I did all the finish grinding I could not get an edge on them to save my life. I ruined a diamond stone trying. I ended up having to sharpen it on my grinder. I am sure it will hold that edge for some time but more than likely (in my opinion) I would have to return to the grinder to sharpen it later. Needless to say I discounted the process (for my use) and now temper my blades even if I clay them to show a hamon. I use a simple heat treat process and 1084 is well suited for that so this process may have worked better with a steel requiring a more complex HT because using my simple HT I would not have gotten the steel to full hardness therefore tempering may not be necessary. (That is the theory behind the process I was testing) I say all of that to say this, what was your tempering process? Unless you finished the knives out completely (like I did) you should be able to draw some hardness out of them and make them useful.
 

Michael Minto

Well-Known Member
#4
I'm using a variable speed 2x72 belt grinder. I made the initial edge bevel on a used 40 grit belt, and went to a 100, then 220. I read a thread here yesterday that spoke of the possibility of having formed a wire edge that was very hard, and that was just getting pushed back and forth, making the edge feel like it was not sharp, even though it is, just feeling dull due to the wire edge that won't go away. I'll be looking with my magnifiers if this happens again, but I'm not going to make any blades that hard in the future. Most of mine are 55/57 on the Rockwell C, at least that's what I shoot for. The knives I make are handled, then sharpened as the last step, so I can keep my fingers. I've always tempered knives I've clayed, being afraid that the edge would be not just hard and keep a sharp edge well, but would also be brittle. Here are a couple of poor quality photos of the fillet knives I'm talking about. Mike
 

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KenH

Well-Known Member
#5
OK, you're using a 2X72 - is it reversible? I run my 2X72 in reverse when sharpening. BUT - anyplace you can get the blade so the belt isn't cutting into the edge, but pulling away from edge. Once you get to 220, then try a 400 grit, then take an old worn out j-flex felt turned inside out so the back side is out, load it with green compound. That will take that wire edge off nicely.

You're right about the wire edge that will form, especially on AEB-L.
 

Michael Minto

Well-Known Member
#8
OK, you're using a 2X72 - is it reversible? I run my 2X72 in reverse when sharpening. BUT - anyplace you can get the blade so the belt isn't cutting into the edge, but pulling away from edge. Once you get to 220, then try a 400 grit, then take an old worn out j-flex felt turned inside out so the back side is out, load it with green compound. That will take that wire edge off nicely.

You're right about the wire edge that will form, especially on AEB-L.
you know, i'm not sure if it's reversible - i'll have to look; funny it never occured to me to check. thanks for the thoughts. mike
 
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