My knives dull right after sharpening!

[JeannieH]

Hi! I'm going crazy here! I have a 1000/3000 whetstone and stropping block. I have two Japanese skiving knives. I can get my knives sharp on stone. Then I strop..then test..still sharp. But, when I pass the knife a few times through my 3.5 oz chrome leather (on top of treated granite..and tried glass) the knives dull! I've tried not stripping...and my sharpness still doesn't last. I can't possible have to sharpen throughout the day..I must not be doing something right. Any tips from anyone? Thanks!

[fredk]

Its the cutting on glass and the granite is dulling your blades fast. Its okay to cut at an angle, eg skiving, but cutting down directly onto the glass or granite dulls the blades. Try cutting on a self-healing cutting mat, or a piece of MDF/hardboard

 

[JeannieH]

Ok. I'm not cutting with the blade straight up and down...I'm skiving...so I mainly lay the flat side of the knife on the leather with the angle side up. It doesn't appear that the blade is touching the granite or glass at all.  It I will try skiving on my mat instead and see what happens. Thanks!

[gigi]

LW user @gmace99  has useful videos regarding sharpening. For example this one, at the minute 1:12. I think the key for a longer lasting edge is stropping and polishing using a mix like in this video. You can also use a ready-made 'sharpening paste' ('honing compound') and a wool felt sharpening and polishing wheel (motorized).

Making a device to keep the sharpening angle constant might also help.  

 

[JeannieH]

Not sure if my message went through so I'm doing it again.  Thanks for the video.  I've watched so many it ridiculous!  I really take my time when sharpening and make sure the angled side is flat against the stone .  I'm thinking the stropping is where the problem is maybe.  The strop already has the compound on it...you can recondition it with a little olive oil.  It is one sided though.  I put the flat side of the angled side on it and pull back...then put the flat side flat and pull back...I've tried putting a slight angle on the flat side.  Doing that made it very sharp...but omggggg it dulls very fast lol!  Ive tried putting barely any pressure on the knife when stropping...tried putting a little more pressure...still dulls fast after getting it sharp.  I had it cutting like butter and was so happy...then bam...dull when I finished that one little piece of leather!

[Art]

This happens when the steel won't hold a very acute edge. For instance, there are a few (I won't name them) head knives that will take and hold 10 degrees a side (20 degrees included) for light duty. But when the steel isn't up to it, the effect is just as you describe. I have found that 18 to 20 degrees per side (36 to 40 degrees included) works for most leather knives.

Art

[MadHatter]

Chrome tan leather with dull an edge faster than veg tan because it has metalic salt residue in it.

Edge angle will effect sharpness longevity. Also edge concave type will also.

Finding the right balance for all the variables will maximize your efforts.

[JeannieH]

Art, I'm not sure I am getting what you are telling me. Lol. I don't know what the angle is on this knife..it's a Nobuyoshi I ordered from leathercrafttools. The 36mm one. Gigi, yes I have read that the chrome tanned leather dulls the knife faster. I don't have a skiving machine so this is my only option right now unfortunately. 

[JerseyFirefighter]

If Japanese cutlery is anything like kitchen cutlery the blade has a different blade angle (15 degree if I recall) over a more common angle of say 25 degrees or therein abouts. This translates into a sharp edge, but can wear more quickly than a more tapered edge. It has been a while since I researched my own kitchen knives but I do recall that point in case with some japanese blade edge methods vs say a German or American made blade. 

[JeannieH]

So Jerseyfirefighter, do I need to try sharpening at a 15 degree angle? I will have to find a tool to make sure I'm holding it at the right angle. I've just been laying the angle side down on the part where it is flat.

[Sheilajeanne]

The problem could be that it's just poor quality steel. Like Art said about certain brands of head knives, they just aren't up to holding a good edge for any length of time.

Not familiar with that brand name - does anyone know if it has a good reputation?

[Jaymack]

+1 on the steel type, quality and temper.

 

[mikesc]

Those edges look "blued" like maybe they have got hot when someone was grinding them ? , if so the temper will have gone off them, in which case they will not hold an "edge" for long at all.

[griley4]

Sounds like it is the steel.....try a different maker if it is possible

[JerseyFirefighter]

8 hours ago, JeannieH said:

So Jerseyfirefighter, do I need to try sharpening at a 15 degree angle? I will have to find a tool to make sure I'm holding it at the right angle. I've just been laying the angle side down on the part where it is flat.

I would think the steel would play a big part in the durability of the knife, however in my limited opinion, using any knife against a solid surface such as granite, glass, OR (as I caught my apprentice doing early on) on top of a piece of steel will create a much faster edge deterioration . I would not cut anything that isnt supported by either a self healing cutting mat, poly cutting board, or even as a quick cut on top of an oak workbench. 

I cannot speak to knife wear while cutting chrome tanned leather, but I believe that Japanese style blades are more finnicky and require a bit more preventative care, regular honing, and expectation that they will need to be sharpened/honed/stropped far more often than a more common blade found in the industry. 

Edited November 16, 2017 by JerseyFirefighter

[YinTx]

Nobuyoshi is supposed to be a very high quality blade.  I don't believe that is a blued appearance from getting hot, I believe it has to do with the types of metal used in the construction of the knife, and the polish done by the craftsman on different sections.  The metal is very hard, can be brittle, and difficult to sharpen.  It will however be capable of sharpening to an extremely thin edge that will hold for a long time.  San-Mai are layered, and can give the appearance you see, as the Jigane and Hagane may take on different hues that shows up in the Shinogi.

These knives are a different world from most knives you see in the leather world, and as such have their own learning curve.  I have yet to master mine - it is the Nobuyoshi , when it is sharp look out.  When it dulls, a challenge for me to get it back to rights again.  Nobuyoshi is super blue paper steel, which is the Aogami steel, which is a very high grade of paper steel.  It is difficult to work with and temper correctly, so it is possible you have one that didn't come out right.  But supposedly this company has been doing it for many years, so they should have the process down pat.  Again, extremely hard metal, difficult to sharpen.  Don't give up on your knife just yet!  Possible you've seen these, but good review on this knife here:

 

And a tutorial on sharpening this type of knife here:

YinTx

[JerseyFirefighter]

18 minute video on how well the knife cuts leather... not one piece of leather cut during video.  I like the look of the knife though. Keeping things sharp are always a pain in the rear. 

[billybopp]

While you would not want to cut through leather on a hard surface, skiving is not problem.  The blade meets the surface at an extreme angle, pretty close to the angle on the blade -  much like it would when sharpening.  

You may need to just stop and strop frequently if the blade is dulling quickly!

Bill

[YinTx]

5 hours ago, JerseyFirefighter said:

18 minute video on how well the knife cuts leather... not one piece of leather cut during video.  I like the look of the knife though. Keeping things sharp are always a pain in the rear. 

LOL, yeah it was a pretty long winded explanation of the knife.  But, I think at the 3:02 mark, that might be a piece of leather making a brief appearance...

YinTx

[JeannieH]

Yintx,  that first video is what made me buy the knife. His review made me feel it was a good one to buy. I have gotten this knife very sharp. Not staying sharp is a downer but I will just keep sharpening as I use it I guess. I will invest in another knife at some point. Any recommendations? Also, the second knife is a double sided Japanese knife I bought from Lisa sorrell. She is a shoe maker. I have the same problem...super sharp then super dull.

Edited November 17, 2017 by JeannieH

[JD62]

What are you using to strop with? Also this is a little better sharpening vid.

 

[YinTx]

Two knives from two different makers with the same problem might indicate it isn't the steel.  Just curious:  what kind of leather are you using it on?  I've heard that some veg tans have clay in them, which is murder on knife edges.  Chrome tans are also hard on edges from what I've experienced.  

YinTx

[Matt S]

I have found that skiving knives, needing to be razor sharp at all times in order to be effective and safe, dull very quickly. This is whether I am using a san mai kiridashi, Swann Morton scalpel, Dixon round knife or English paring knife. For a time I was using disposable scalpel blades but even buying by the hundred that got expensive quickly, especially on chrome tans. Currently I use an equal-bevel kiridashi (so I can pull and push) with amalgamating tape round the handle. It has a very hard core with softer steel sandwiching it. I have to strop very regularly to keep the edge in top form.

[machinehead]

I have both the narrow and wide versions of the knife that Lisa Sorrell sells and they hold an edge well and strop quickly back to super sharp. Lisa uses these knives herself to skive the inlay and overlay pieces for her custom cowboy boots. In case you haven't seen her video on sharpening these knives:

 

 

Edited November 17, 2017 by machinehead

[JeannieH]

I'm using the stropping block from knives plus. I have watched the video on fixing Japanese skiving knives and Lisa sorrels video a while back. I'm skiving 3.5 ounce chrome tanned leather with a soft hand. When I strip, should there be any pressure applied to blade or just lightly pass it over the strop?