A new edge for a Sebenza 25

[kwakster]

The owner of this Sebenza 25 bought the knife brand new through an official dealer in the Netherlands, but although he was and is still very pleased with the knife itself, he soon found that the factory edge didn't cut too well.
He tried to improve things with the help of a Spyderco Sharpmaker and a leather strop loaded with some green compound, but to no avail.
So he sent the knife to me, and the first thing i did was to measure the edge angle.
According to my Tormek Angle Gauge it measured 50 degrees inclusive on the straight part of the edge, going up to 55 degrees inclusive from the belly to the point.(!)
This is how the knife looked before sharpening:







First i removed the apex of the old edge by cutting a few times directly into an old silicon carbide stone, after which i reprofiled it freehand on my Tormek SB-250 Blackstone to an even 30 degrees inclusive.
This was followed by a Paper Wheel with 220 grit SiC to smoothen the grindlines made by the Tormek, then refined with a second Paper Wheel coated with 15 micron diamond compound, and finally removed the burr with a third Paper Wheel coated with 0.25 diamond compound. (this leaves the 15 micron scratch pattern intact as much as possible to preserve bite)
The resulting edge treetops the hair on the back of my hand, can slice single-ply toilet paper, and survives a few cuts into my laminated testblock without any visible damage (checked under bright light with the loupe in my Victorinox SwissChamp)
This is how the knife looks after sharpening:

[sir_mike]

Wow, very nice job!  I wish I could sharpen that good!  I also wish you were closer so you could sharpen a few of my knives!

[RT1969]

This looks like a really good new edge! 

In the close-up from the old grind (Was this really the factory grind?  ) it looks like the edge is well polished, but rounded. (See the distorted reflection of you near the tip)
Maybe it was 'over-polished' and therefore the edge to broad?

[harronek]

Wow

I wouldn't know where to begin , that's impressive   


Ken

[sticktodrum]

Very nice. I'm curious, why did you remove the apex before reprofiling the bevel? I've never heard of that before, and would like to learn more.

[kwakster]

This looks like a really good new edge! 

In the close-up from the old grind (Was this really the factory grind?  ) it looks like the edge is well polished, but rounded. (See the distorted reflection of you near the tip)
Maybe it was 'over-polished' and therefore the edge to broad?

What you see in the first series of pics is indeed the factory edge, of course after the owner tried in vain to solve the problem of the large edge angle with his Sharpmaker & strop.
So the fine scratch pattern with a bit of shine you see in the first pics is indeed his work, but the large edge angle was already there from the factory.
I sharpen Sebenza's on a regular basis, and many of these have a widening edge angle towards the point, sometimes so much so that owners are unable to sharpen the complete edge with a Sharpmaker alone.
But i've never seen it as bad as on this 25.

[kwakster]

Very nice. I'm curious, why did you remove the apex before reprofiling the bevel? I've never heard of that before, and would like to learn more.

Old apexes often consist of weakened metal because of use (chips & rolls), steeling, and previous sharpenings.
In kitchen & butcher knives this can be observed to the extreme as many chefs and butchers almost constantly steel their knives during shifts, thereby forcing the apex from the left or right to the center, over and over again.
Compare it to a paperclip which you bend back and forth: if you do that long enough the metal weakens and breaks.
The same thing applies to the apex of a knife, an area much thinner than a paper clip which gets to handle tremendous forces sometimes.
I've noticed an increase in edge holding when i started to remove the old apex before sharpening a new one a few years ago, and it works on all kinds of knives.

[RT1969]

Very nice. I'm curious, why did you remove the apex before reprofiling the bevel? I've never heard of that before, and would like to learn more.

Old apexes often consist of weakened metal because of use (chips & rolls), steeling, and previous sharpenings.
In kitchen & butcher knives this can be observed to the extreme as many chefs and butchers almost constantly steel their knives during shifts, thereby forcing the apex from the left or right to the center, over and over again.
Compare it to a paperclip which you bend back and forth: if you do that long enough the metal weakens and breaks.
The same thing applies to the apex of a knife, an area much thinner than a paper clip which gets to handle tremendous forces sometimes.
I've noticed an increase in edge holding when i started to remove the old apex before sharpening a new one a few years ago, and it works on all kinds of knives.

A lot of insight and experience here. I love it! kwakster, thank you for sharing! 

[JAfromMn]

NICE WORK kwakster

[Sparky415]

A lot of insight and experience here. I love it! kwakster, thank you for sharing! 

+1 

[microbe]

Nice work!

[sticktodrum]

Very nice. I'm curious, why did you remove the apex before reprofiling the bevel? I've never heard of that before, and would like to learn more.

Old apexes often consist of weakened metal because of use (chips & rolls), steeling, and previous sharpenings.
In kitchen & butcher knives this can be observed to the extreme as many chefs and butchers almost constantly steel their knives during shifts, thereby forcing the apex from the left or right to the center, over and over again.
Compare it to a paperclip which you bend back and forth: if you do that long enough the metal weakens and breaks.
The same thing applies to the apex of a knife, an area much thinner than a paper clip which gets to handle tremendous forces sometimes.
I've noticed an increase in edge holding when i started to remove the old apex before sharpening a new one a few years ago, and it works on all kinds of knives.

That hadn't occurred to me before. Brilliant! Thanks for the information, I'll definitely give that a shot the next time I have a reprofile to do on a blade.

[kwakster]

A few days ago i sent the owner of the knife a message asking him how the edge was holding up in his use, and today i received this reply (translated from Dutch)

"During our week & a half holiday in Normandy, France i've used the Sebenza 25 lightly, but daily for opening packages, cutting string, and cutting bread (not on a board)
Afterwards when i pulled the edge over my thumbnail i could feel a few ever so slight irregularities, but these disappeared with just a few passes over my strop.
I would still consider the knife to be very sharp: it won't treetop the hair on my arm anymore, but it still shaves it effortlessly on skin level."

This was my answer:

"To me the higher degrees of sharpness (hairwhittling & treetopping) are in fact only useful to find out how sharp exactly a certain steel will get with a certain sharpening method.
In daily use however these sharpness levels will vanish quickly as soon as the knife is used for more than just mowing hair from your arm.

If at this moment the edge is still able to shave the hair on your arm on skin level i would consider that a good result, and actually even a bit above my expectations considering the lower hardness of earlier Sebenza blades in S30V and S35VN (based on previous Sebenza's i've sharpened as well as user feedback)
My guess is that the hardness in the Sebenza 25 model is ramped up a bit compared to earlier versions, something i consider to be a good thing.

Those slight irregularities you feel with your thumbnail could also very well be sticky debris clinging to your edge instead of damage.
Something even slightly sticky can hang on to your edge tenaciously making it many times thicker and more irregular, thereby making it only seem like there is edge damage while in fact there is none.
My advice would be to only do the thumbnail test after you've cleaned the edge well (i use a soft piece of cotton with some acetone for this) to make sure it's really clean.
If after this you still feel irregularities then it's truly damage and it maybe time for the strop.
BTW: using any strop before cleaning the edge of a knife will very quickly lessen the effectivity of the strop by fouling it.

I would recommend to use the Sharpmaker when the edge is no longer able to shave armhair, as it is way easier to keep your edge sharp with it than it is to make it sharp.
Also because a strop is no magic wand: when you let your edge degenerate too far a strop won't help you out, no matter how long you keep stropping.( it will even work counterproductive)
I only use a strop on already very sharp edges to keep them at a certain level (not to get them there), and only sparingly: just a few stroppings per side should do the trick.
My advice would also be to get yourself a diamond loaded strop as this will work more efficiently on the hard (vanadium) carbides in the S35VN steel compared to your current one with chromium oxide."

[jacktrades]

Great work on that edge.