can you have a blade that will just not take an edge? UPDATED - Thank you forum crew!

kidcongo

kidcongo

Joined
Jan 12, 2013
Messages
3,195
Guys and Gals,

I am no newb to sharpening. I have been in this hobby for serveral years now, and own quite a few CRKs and several Spydercos, as well as some fixed blades. All my knives, excluding one or two, are daily users in rotation. All of my CRKs, including several Sebenza 21s, I can sharpen successfully, but one: my first 21, which is a standard point, micarta, made in 2012, S35VN. I have a few sebenzas of similar vintage (before the hardness upgrade) that cause me no grief. It is not that this particular knife takes an edge and then goes dull, it seems to simply not take an edge. It has been sharpened on rods (sharpmaker), loaded strops, and free-hand on a bench stone in my endless quest to get this knife sharp, but none of these techniques seem to work. My efforts with everything else I do are satisfactory.

So, my question:

Can a blade with some sort of metallurgy issue (too soft, too hard etc) behave in such a way that no sharpening technique will produce a nice shaving-sharp edge on it? Remember, I am not worried about edge retention, I just cant get a good initial edge on this one blade. Is it maybe a fubar blade?
 
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I cannot speak to the ifs, whys, hows, etc. but to add an anecdotal nugget of information, I once had that exact same experience on a Case knife with their Tru-Sharp stainless steel. Again, no idea why this happens, but I agree with you that it can and does happen.
 
My experience with CRKs is that the bevel is sometimes ground at a too flat angle. Maybe your're not touching the actual edge when you are sharpening at say 40 degrees and just working on the shoulders. Have you marked the edge with a sharpie to see if you're really sharpening the edge?
 
Do you think that the metal is soft and whatever you're using to sharpen with is getting clogged with metal more so than your other blades? Thus, making it almost impossible to get it sharp.
You may have to clean the rods/stones during the sharpening process in order to get it sharp.
We're accustomed to thinking every blade should take about the same effort to get it honed the way we like it. And normally that's the way it pans out.
The other issue I've ran into because I'm not consistent in free hand sharpening is getting off on the bevel. Most of the time I run a ceramic rod and strop to get a blade back to the sharpness I like. But, every so often, I use a guided system to straighten the edge back out so I don't screw up the edge.
From what I've experienced with a bad heat treat is the blade chipping when you get close to the apex of the edge.
 
No, I don't think I have. Usually can get it sharp for at least a little while.
Now I've had a knife from a well known, high cost, mfg that had a bad HT, it kept an edge for long enough to hold your breath, but I could still get it sharp.

Ajack60, your last line makes sense.
 
So far, some really good ideas, so thank you all. I will try cleaning the stones and renewing my strop. Another thing I'll look at is if this 21, for some reason, is more obtuse that my others. On the metals side, I sorta wonder if this batch of S35VN was simply low on Vanadium, or the part of the ingot that made my blade was. IE: it has no carbides?

The ridiculous thing is after making this post, I was sitting effortlessly carving paper and shaving arm-hair with my Bark River Bravo 1 (also in S35VN), which is a giant chunky knife, and my old 21 can barely make it through a inch of paper without jamming up, and not much shaving.

I gotta get to the bottom of this. It's been bothering me for a very long time (obviously).
 
I had zero luck getting my two S35VN Sebenzas sharp using a Sharpmaker or strops. It wasn't until I finally broke down for an entry level Lansky with diamond stones that I finally, after years of struggle, was able to get my 21's hair popping sharp. I practiced reprofiling on my cheaper stuff first and then SUCCESS!

Sent from my HTC6545LVW using Tapatalk
 
in mass production heat treat, not all the blades get the love they deserve.
 
Never had any knife I could not get sharp enough for my uses, but then again if I want to shave hair I use a razor and never have understood whittling hair. My knives are sharper than the chefs and prep persons use in our restaurants. To me that is sufficient.
 
It COULD be a bad heat treat, although a true bad HT is pretty uncommon...but...as with any diagnosis-- go for the most likely issues first...so I'd say check to make sure you're not leaving a slight wire edge or over-stressing the apex...

It's more common to experience what you're seeing when you form a really good apex but it's weak and likely to fold over or blunt with even the slightest pressure...sounds familiar, right? ;)

if you're certain that you're hitting the apex when you sharpen <because that IS the point of sharpening...pun TOTALLY intended :p>...try "erasing" the apex you just expertly formed by very lightly drawing the edge perpendicularly across the face of the med rod a few 5-6 strokes to remove <what may be> overstressed metal at the very apex...

then re-apex into the virgin steel using light strokes and being sure to avoid burr formation as much as practical....

at that point, if your steel is hardened correctly you should have a nice, hard & tough & consistent apex with a solid foundation...

keep us updated!
 
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peterbright said:
Never had any knife I could not get sharp enough for my uses, but then again if I want to shave hair I use a razor and never have understood whittling hair. My knives are sharper than the chefs and prep persons use in our restaurants. To me that is sufficient.
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I appreciate you chiming in, but the point is not that I need this Sebenza razor sharp, just the observation that this one knife, out of my collection of 21s, behaves very differently than its brethren, and can't seem to take a razor edge, whether or not that's a requirement of my daily life.
 
PeteyTwoPointOne said:
It COULD be a bad heat treat, although a true bad HT is pretty uncommon...but...as with any diagnosis-- go for the most likely issues first...so I'd say check to make sure you're not leaving a slight wire edge or over-stressing the apex...

It's more common to experience what you're seeing when you form a really good apex but it's weak and likely to fold over or blunt with even the slightest pressure...sounds familiar, right? ;)

if you're certain that you're hitting the apex when you sharpen <because that IS the point of sharpening...pun TOTALLY intended :p>...try "erasing" the apex you just expertly formed by very lightly drawing the edge perpendicularly across the face of the med rod a few 5-6 strokes to remove <what may be> overstressed metal at the very apex...

then re-apex into the virgin steel using light strokes and being sure to avoid burr formation as much as practical....

at that point, if your steel is hardened correctly you should have a nice, hard & tough & consistent apex with a solid foundation...

keep us updated!
Click to expand...

More good advice. As much as it might pain me to purposely dull a knife I've struggled to sharpen, I will try your idea of discarding what I have and starting over.
 
kidcongo said:
More good advice. As much as it might pain me to purposely dull a knife I've struggled to sharpen, I will try your idea of discarding what I have and starting over.
Click to expand...

Well, look at it this way, considering you pretty much wind up dull after light use, it won't be that big a loss from what you're already experiencing...;)

Also, remember you're just LIGHTLY dragging it across the hone, basically using the weight of the knife itself...in essence probably removing just a few microns of stressed steel at most...

I use the flat of the rod for this, but the corners of med rod might yield even better results for you...

if you've done it correctly it shouldn't take a min or two to reapex-- it's not like you're gonna have to rework thru your entire grit cycle protocol to get back to nice clean refined apex.

I try to imagine I'm using the same "finesse" as I do when I'm very very lightly removing a burr or applying a microbevel.

Sorry if I'm being over explanatory...I know you're not a noobie-- I've learned more from your posts than you'd imagine...just trying to return the favor just a little bit!:)
 
PeteyTwoPointOne said:
Well, look at it this way, considering you pretty much wind up dull after light use, it won't be that big a loss from what you're already experiencing...;)

Also, remember you're just LIGHTLY dragging it across the hone, basically using the weight of the knife itself...in essence probably removing just a few microns of stressed steel at most...

I use the flat of the rod for this, but the corners of med rod might yield even better results for you...

if you've done it correctly it shouldn't take a min or two to reapex-- it's not like you're gonna have to rework thru your entire grit cycle protocol to get back to nice clean refined apex.

I try to imagine I'm using the same "finesse" as I do when I'm very very lightly removing a burr or applying a microbevel.

Sorry if I'm being over explanatory...I know you're not a noobie-- I've learned more from your posts than you'd imagine...just trying to return the favor just a little bit!:)
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Absolutely, and much appreciated. Over-explaining is never a crime on the CRK sub-forum. Thanks again!
 
Edge of the blade was probably overheated during initial sharpening, definitely do as suggested above, set the bevel then remove the fresh edge and start over with hopefully fresher and better steel. An overheated edge will do just as you describe. Also use a sharpie on the edge to make sure you are in fact getting to the edge on both sides an minute burr can do as you describe as well and some steels when run in the softer side like CRK will tend to burr pretty easy if you don't hit the apex cleanly.
 
One other option to remove user error, send it in for spa treatment and see how the edge lasts after a fresh factory sharpening. I expect CRK could be able to do a hardness test as well to check the heat treat.

Good Luck in what ever you decide!
 
kidcongo said:
More good advice. As much as it might pain me to purposely dull a knife I've struggled to sharpen, I will try your idea of discarding what I have and starting over.
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This is what I do. Start from scratch. Cut off the apex, get out a DMT XC or C, and regrind a new apex.
 
And use a sharpie on the edge to see where you are hitting the stones, just to be sure.
 
A big THANK YOU to all my CRK pals who chimed in. You were right! I have a very sharp knife now, so I guess it was not a bum blade. Here is what i did and found out:

1: Taking the advice here, I stroked the blade about 8 times perpendicular, and firmly, to a white (fine) Spyderco bench stone (ouch!!). I verified that I could see light reflecting along the whole edge, indicating the old apex was no more.

2: I soon discovered that this blade was certainly hardened properly, as what I thought would be maybe 1/2 hour of work to restore the apex became something I accomplished over a couple evenings. I started using the brown Spyderco Sharpmaker stones on edge, at 40 degrees (inclusive), and began taking away the old steel, followed by switching the stones to flat, just as Spyderco recommends (being very very very careful not to let the blade tip slip of the corner when the stones were on edge). At this point the sharpie technique really didn't work because there was no apex to miss, if you know what I mean. The apex was basically squared off so the sharpening at this point was a process of narrowing the flat section I created by dragging the blade across the stone into a new apex

3: with the apex being flat, my guide for sharpening was looking for light to reflect off the edge. I set up a small task light at the prefect angle to see this. After an hour or so of carefully working the blade on the brown stones, I still wasn't completely there. I cleaned up the scratch pattern bevels on the white "fine" stones and called it quits for the evening.

4: on 'Day 2' I started in again on the brown medium stones (I do not own diamond stones or anything like that), and kept it up until I had a "ghostly" edge that would reflect no light. At this point I knew I was back at a 40 degree (inclusive) bevel.

5: I then switched to the fine and finally the extra fine stones, with extra time spent on each. Following that I stropped the blade lightly with a leather strop with fine (white) KSF compound. The blade was now shaving sharp.

6: I decided to slightly polish the shoulders of the apex bevel using the Sharpmaker set at 30 degrees (inclusive) and the extra fine stones. This just removed a little scratching and damage to that part of the blade from normal use of the knife.

THE RESULTS: HOLY SMOKES!!!!! Sharpest knife in my collection. All this time (years actually) I think I was fighting a weird convex edge, that I maybe aggravated through my own stropping, and perhaps some less-than-great steel on the edge from the factory sharpening process or heat treating. After many years of this knife disappointing me, it is finally, and truly, super sharp. I think also this blade is perhaps a little harder than the other 21 blades I have, so maybe it needed more time in the past to sharpen it that I was willing to invest.

Will it stay that way? Edge retention has never been my complaint on this knife, but I imagine, like any S35VN, the nice edge i put on will quickly dull to a durable "working edge" that will last a long time. It is nice, however, to see this knife truly sharp for the first time in it's life. Thank you to everyone who pushed me to start over. That was the best thing to do.

We are now s-cutting paper with a quiet swish, shaving arm hair, and reflecting light like a mirror, with this crazy edge. I love it!

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