Choosing stones for sharpening specialty trade knife

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pierat

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Nov 26, 2010
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My primary work knife is called a Kobito, made by Aesculap Medical. It is basically a reusable x-acto or scalpel made by a surgical tool manufacturer for the shoe and leather industry. The business end of the blade is about the size of an x-acto, but thicker and about 6 inches long into the handle. You just advance the blade and sharpen when necessary until it's gone. It's really a cool knife. I use it to cut all my cardstock patterns, leather parts and heavy fabrics like cordura. This is the knife. https://shoetechnik.com/kobito-leather-knife.html

In the past, I never really sharpened this thing beyond 400 grit, because it dulled so quickly that I would have to sharpen it every day anyway. A refined edge was pretty much gone after 10 minutes of work, after which it needed honing every 10 minutes, which was no different than a less refined edge. So I settled for the toothy edge. But I just started hardening the blade with a quick torch and quench and edge retention is amazing now. Honing is down to about 10%-20% of what I needed before. I am able to see huge benefits from taking it up to 1000 or 6000 on my King KDS. Unfortunately it’s harder to sharpen now and the King cuts too slow. I need to start using diamond. I could get by with Edge Pro sized plates, but for about the same money, I can get full size Atoma plates on Amazon and use at least one of them to lap my King KDS 1000/6000 and they can also be used on my larger knives too. But I don’t know what grits to get. I tried sharpening this blade on paper to see how it worked. The only grits I had that were appropriate were 220 and 400. It put a great edge on. I would have finished it on the King 1000, but didn’t want to wait for it to soak this time around. I splashed my King 6000 and polished it a little and it turned out really nice. I think taking it to around 1000 is appropriate for regular use, but would settle for coarser if I could avoid a third stone.


Looking at the Atomas, the grit progression is not really set up well. Seems most people opt for using one or two Atomas and adding more grits of a different medium. I would like to have just two grits, or three if I could avoid soaking, and keep sharpening at work quick and tidy. I think the 400 would be good for lapping my King stones, but then 140 seems too coarse for starting on. I could go 400-600, but that isn’t enough progression to spend that much money on. So I am wondering if I should just try 140-400 and find something else in the 800-1000 range to finish on. Or, would the 400 cut fast enough that I could skip the coarser cutting I got from my 220 paper and just go straight to the 800-1000 and call it a day? But if I lap my King stones with it, will it remain coarse enough for long enough? And finally, any recommendations for the fine 800-1000?

I would like to stick with diamond because I hate having to wait for soaking at work, time is money. Splash and go stones sound good, but still are messy and everything I’ve looked at seems to cut slower that a water stone. Atoma 1200 is an option, but not sure if going from 400 to 1200 is going to satisfy me. I just wish Atoma would make an 800, my problems would be solved.


Thanks for taking time to help!
 
Since that tool is small, you could look at using smaller diamond plates to save some money. DMT has a line of dual-sided 6" plates. Take a look here for some ideas: https://www.knivesplus.com/DMT-Knife-Sharpener-Dia-Sharp.HTML You could get two different mesh sizes on a single plate for around $50.

The Atoma progression is 140 - 400 - 600 - 1200. The DMT progression is 220 - 325 - 600 - 1200. These are based on different standards - the Atoma fits into the JIS standard, and tends to have slightly larger particle sizes (listed in microns) than the DMT so they are a bit coarser at every listed "grit" than the DMT would be at the same listed grit. The Atoma 1200 is going to be somewhere between the DMT fine and extra fine. Probably a little finer than your King 1000 (which also uses JIS).

You can also find the SK11 diamond plate, which is a dual-sided plate listed as 400/1000, for under $40.
 
Thanks for the tip Cereal Killer.

Jc57, yes, the blade is really small. I got to thinking about it some more last night. I realized that I can only use about one inch of the stone because due to the angle, I can't hold the blade any way but over the edge of the stone. So with a large plate, I will be unable to the full surface evenly. I guess I can use all 4 edges, or get a smaller plate. But I wanted a larger one for lapping my other stones anyway. No point in buying both. I was looking at the sk11 last night, too. I'd love to save money, but if I am not happy with a cheaper alternative and end up buying an Atoma after anyway, that will cost me more. Decisions, decisions.
 
pierat said:
Thanks for the tip Cereal Killer.

Jc57, yes, the blade is really small. I got to thinking about it some more last night. I realized that I can only use about one inch of the stone because due to the angle, I can't hold the blade any way but over the edge of the stone. So with a large plate, I will be unable to the full surface evenly. I guess I can use all 4 edges, or get a smaller plate. But I wanted a larger one for lapping my other stones anyway. No point in buying both. I was looking at the sk11 last night, too. I'd love to save money, but if I am not happy with a cheaper alternative and end up buying an Atoma after anyway, that will cost me more. Decisions, decisions.
Click to expand...

Looks like you are getting dialed in on what you want, but I will throw my bit in anyways...I have often regretted going with the cheaper alternative and sometimes have to go back and get the more expensive one later after the cheap one fails to perform to my needs. Get the good one now, feel the pain and scrimp a bit to recover the budget, and you will only have to make the choice once.
 
View attachment 822526 You might want to take a look at the Bonded Diamond Venev stones. They cover 6 grits with 3 stones. The diamonds are mixed into the substrate rather than being codeposited with Nickel in a plating bath. They work great with just a little water spritzed on.
 
Those Venev stones looks really good, thanks for the recommendation. The ability to have diamond with a surface that reveals new abrasive instead of wearing down seems like a good bet. I looked at diamond waterstones in the past, but the price and inconclusive reviews I read didn't make me want to jump on them. This one looks pretty darn good, though. The 4 lowest grits would probably be perfect, price is good. My only worry is about how to flatten them. Doing some more research now.
 
Hi pierat,
Here what I read
- Kobito leather knife , like utility/snapoff blade, 6mm width, 1mm thick, either carbon or stainless
- never really sharpened this thing beyond 400 grit,
because it dulled so quickly that I would have to sharpen it every day anyway.
- 1k-6k edge gone after 10 minutes of work, after which needs honing every 10 minutes
- But I just started hardening the blade with a quick torch and quench and edge retention is amazing now. :confused:
- Honing is down to about 10%-20% of ???, see benefits from high grits 1000 or 6000 on my King KDS.
- It’s harder to sharpen now and the King cuts too slow
- I need to start using diamonds for speed
- soaking stones takes too long
- splash and go is still messy
- and seem slower than water stones

The way I understand/translate what you're saying
- maybe the manufacturer sold you defective knife blades, not uncommon, but likely not your issue

heat treating the blade yourself is extreme,
but no matter how hard you get it,
the aluminum oxide in the king stone is still harder than steel and will cut it as fast as diamonds,
these blades aren't high carbide steel
but waterstones can be tricky


- so maybe your sharpening and/or cutting technique could use a tweak
because
- 10min of cutting shouldn't dull your knife
unless your leather is covered in sand,
or you're cutting on a metal/concrete table

- so either the knife is not very sharp to begin with ,
can't shave or better whittle hair
because there is a burr
or the apex is damaged (like a really thick burr) because of too much force used
or the apex isn't set (mud on muddy stones keeps edge below hair whittling )

it could be all you need to do is lighten the force you use ,
and flush the mud from the stone,
before you set the apex
or change the way you set the apex
do light edge leading alternating passes, with 2 double angle deburring passes
or if that isn't working,
do 1-10 light alternating edge trailing passes on the flushed king 1k/6k,
then 1-10 edge trailing passes on newspaper or leather to remove burr

you might also need to flatten your king waterstone, as it goes out of flat, the curvature/holes effectively increase your sharpening angle, which is why water stones can seem to be faster

- or the sharpening angle is too low (under 30 degrees inclusive ) for the type of cutting you're doing,
and/or the amount of force you're using when cutting,
esp the amount of side loading you're putting on the apex,
so the edge rolls to one side or the other within 10min

if the edge rolls,
pretend you're a chef,
and instead of sharpening,
strop a few passes to unroll the apex
then continue cutting for another 10 minutes
you can use almost anything to unroll the rolled over apex ,
plastic, ceramic, or even butchers steel, ceramic mug/tile ...
on mug/tile you can even do a few edge leading passes (sharpening)


one solution to soaking time,
is keep the king waterstone permanently soaked ,
so they're always ready for action
it won't damage the kings


so please tell us/me how sharp you get these knives and how exactly you sharpen them
are you using microbevels?


So stones you might need?
Not sure you need atoma or sk11 or ... kings are soft ,
and
all kind of cheaper (as in $20/$10/$5/$3 ) diamond plates can be just as durable, see
Quick combi diamond plate comparison

Since the kings are soft, for easier apex setting (microbeveling)
One of those 3000#/10000# 4" or 6" oil stones might come in handy
hard like arkansas stones but can be bought for about $5 shipped
 
Bucketstove,

Thanks for bulleting my points. I tend to rant type as if I was explaining it verbally off the top of my head. This post will be worse because it's been a long day and I am crashing. Just wanted to reply before hitting the sack. So pardon another messy post! :-)

First, I had originally type this in my post, but deleted it because the post was going to be too long. I don't think having a bad blade has anything to do with my issues. I have used about a blade a year over the past decade and have never seen anything different between them. I have about 5 more replacements here I could check, but they have always been about the same. The real problem here is that my cutting surface is a 4' x 8' table with a sheet metal top. I know, it sounds crazy and dumb, but I cut directly on steel. So the leather, nylon, bonded leather, chipboard, cardstock, polycarbonates, polystyrene, paper.....all the stuff I cut, is not what damages the blade. It's simply the steel cutting surface. Generally, only the very tip touches the surface, so I only have maybe 1.5mm of the tip that gets dull. I use a shallow cutting angle which lets the parts of the blade that never touch the steel do all the work while the tip just drags on the table. By the time the cut gets to the tip, the leather is 90% cut already, and the last 10% is basically the part I am honing frequently. We use steel because we use a lot of magnets to hold things down, and it is better than a "self healing" surface because you can make repeated cuts on it in the same place without cutting a deep groove that never actually heals. There are more reasons, but that is some basics of it. I have been cutting this way for over a decade, honing is second nature and I don't even look at my hands when I do it anymore, it's in muscle memory. I should also add that when I say honing, I mean on a round honing steel. I use a tiny F. Dick chef's pocket honing steel. I am not running to a stone to hone every 10 minutes.

As for the angles. The angle of the blade is about a 20 degree line. The bevel I am using is about a 12 degree double bevel. Until I started this hardening test, I used a chisel bevel of 30 degrees and did much of my sharpening with a medium flat file, only following up with higher grits when I needed to. The chisel bevel was used for ease of sharpening, but it was always a problem because sometimes I need to cut on the left of a pattern piece and sometimes the right. Cutting on the left with a chisel grind on the right always caused problems, but I proficient with it and adjust by holding the blade at an angle to compensate. Having a double bevel now, it has been so much easier in that sense. Now that I started hardening, I first tested with standard double bevel, then I tried a convex bevel which worked great, but it was a little more work to do right. Now I have found a plain old flat bevel works fine. I have made a jig to hold the angle from some thermoform plastic. It works alright, but is made to slide on a granite surface next to the stone, not on the stone like a chisel jig. With a diamond stone that never dishes enough to change the height much, that's fine. With a water stone, flattening would mean I have to flatten my jig to match every so often, which won't work out well. However, I can grind this bevel by hand without the jig just fine, it was just something I tested and would love to be able to use. Doing it by hand, I know I will never hold a 12 degree bevel and it will wind up with a +/- of about 4 degrees. That is still good enough, just not perfect. I may machine a good jig in the future to make it easier. But after 13 years of doing it by hand, I don't mind continuing to do so.

My King is not flattened, but I do use my itty bitty diamond plate to even it a bit and raise a slurry. It also hasn't seen much use, so it's in good shape. I do not permasoak it, I have seen bad results from reviewers permasoaking a KDS.

I'm not sure what you mean by double angle deburring pass. I will look it up or think about it when I am not exhausted and it will probably make more sense. I know my technique is lousy. I started sharpening my own knives about 20 years ago, but I have never done it frequently enough to get very good at it. This particular knife I have never treated like a fine blade, so something this tiny is a steep learning curve for me at this point.

Finally, I have tested a microbevel in the past before I tried hardening it, with both the chisel grind and the double bevel. It never worked any better due to the steel cutting surface destroying it. I have not tried it again with the hardened blade, but I have no reason to because the blade last ridiculously long now. Maybe it will be an improvement, but right now it's so good I can't imagine it being any better.
 
Hi
pierat

yeah I know what you mean about these text boxes :)

you seem to have a pretty dang good understanding of this sharpening thing,
your cutting process seems well though out and well practiced,
and only letting the 1.5mm/10% of the tip touch the metal is genius , :):thumbsup:
in my kitchen we're lucky if we only use 1.5 inches

+/- 4 degrees sounds pretty dang good control for freehand

so your edge is 12 degrees per side +/- 4 ... so about 24-32 total angle
Maybe you can try adding a few
10 alternating passes on the stone
at 25 degree per side
for the 2mm of the tip of the edge thats cutting against the metal table
That ought to get you more than 10 minutes between steeling/burnishing




good camera angle but slow explanation of double angle deburring Shearing off a Burr Using High Angle Passes - Steel Drake
basically if you're sharpening at 20 degrees per side,
to remove burr do ultra light edge leading alternating 2 passes
at 40 degrees per side (like the max angle)
if you're sharpening at lower angle,
ex 7 degrees per side like drake does in video,
you don't have to jump as high as 40,
doubling the angle is more than enough for freehand,
but no precision is required just ballpark it
 
Having only the tip of the blade on the table helps, and it's usually the only part that becomes dull very quickly. However, the very tip of the point is important to get good precise cuts when I need to. Like when cutting an inside corner, if the tip isn't sharp, there will always be some material left right where the corner meets that the tip couldn't precisely cut. Then, I need to cut it by lifting and using a different part of the blade that is still sharp. Now that the blade is sufficiently harder than the table, this is no longer a problem. So that's great so far.

+/- 4 degrees is what I get when I am trying really hard. That is my goal. I don't know that I am actually getting that on a regular basis when working quickly. But since the blade lasts longer now, it isn't a waste of time to put more care into the sharpening. So I think I will be close to that.

Thanks for the suggestions, I will try this. You're recommending a bit of a microbevel on just the tip of the blade if I understand that correctly, right? That's an interesting concept I never thought about.
 
I use a very, very sharp blade that contacts metal with nearly every stroke, so I have an appreciation of the problem you describe. In fact, my blade edge runs into the edge of a 0.2 mm piece of steel nearly every pass of the blade.

I found the Norton fine India stone good at both resharpening and burnishing the edge. And like you, I have to do this continuously. Alternatives that work are: ceramic honing rods, smooth steels, and higher grit wet/dry sandpaper depending on how the blade is set up and the work station.
 
pierat said:
Thanks for the suggestions, I will try this. You're recommending a bit of a microbevel on just the tip of the blade if I understand that correctly, right? That's an interesting concept I never thought about.
Click to expand...
Yup, a seperate microbevel just for the tip,
close to but not quite a cold chisel angle (for metal cutting)
of 30 degrees per side (60 degrees inclusive)
 
Since I've never owned a diamond bench stone (only had the Smith jig sharpener with itty bitty 0.5" wide plates), I want to get my feet wet with diamond bench stones and see how it goes with this knife. I ordered an SK-11 150/600 today. For $28, it's a good buy even if I don't like it for this application. I can use it as a lapping plate for my King KDS combo until it dies, or just throw it in my truck for a rainy day. It arrives on Monday, so I'm sure I'll be grinding as soon as it arrives and will report back with results.

If I have some time this weekend to try the suggestions here, I'll give that a whirl.

Thanks again for all the responses here. After close to 10 years of lurking the board, and getting plenty of information without even a single post, I am pleased to see how helpful you all have been on my first post about a specific personal need I have. Glad to actually be an active member now!
 
Interesting to see a real work usage of a blade. I guess it counts as hard use ;)

How about a DMT credit card extra fine? From your description of how you use it, it’ll give enough toothiness, doesn’t remove metal much (because of higher grit) and can also be in your pocket? Alternatively, DMT diasharp folding sharpener in F and EF.
 
I did mention earlier that a credit card sharpener would be sufficient do to the small size of the blade. I could have opted for this first, both for economy and for convenience. However, I decided to look for full size bench stone plates because I am also in need of a more coarse, full sized stone for repairing my kitchen and butchering knives, and also something for lapping my water stones. I think once I find what works the best for my daily use work knife, I will most likely look for a smaller plate or credit card sized sharpener to use exclusively at work. Until then, I would prefer to spend my money on something I think I can use at home in case it isn't what I want at work.

Unless I can change my sharpening technique by finding a way to hold the knife in a way that will allow me to use the full stone, rather than my hands off the edge of the stone so I don't drag my knuckles, I will only be using the outer 0.75" of an 8"x3" stone anyway. In this case, I know I will be wasting my money in the long term buying more surface than I will ever be able to use with this knife. So, your right, a credit card sharpener, pocket sharpener or smaller plate made for something like an edge pro will be more economical in the long term. I just don't know what I will need yet, so I am only sticking to larger stones so I can use them in another way if it doesn't work out.

As for the DMT grits you mentioned, I would like to try them. I don't own any DMT plates yet. I may opt for buying a few options in smaller sizes of various brands to save a little money. However, in my research it seems for very little more money I can get larger bench stones. Not much more investment gets me much more abrasive by going big. Worst case scenario, I can put one in my truck, one in my camping gear, another in my kitchen, and if I get too crazy, start giving them to friends and family. Ideally, I would like to find something that works before I have to buy too many options to test, though. I'll try this SK11 first. If I don't like it, I'll buy a DMT and an Atoma before anything else.
 
The SK11 156/600 plate just arrived from Amazon. Before putting my tiny blade to it, I sharpened an extremely dull carving knife to break in the stone a bit. Just to try it, I did a couple passes dry and it was not pretty. So I lubed up the plate with paraffin lamp oil. The only diamond sharpeners I've had before were continuous. The grid pattern on this stone really makes the diamond, which already feels kind of uncomfortable, even worse. The grid is 45 degree lines making diamond shapes. So sharpening at a 45 degree angle of approach gives the blade all these little tracks that it wants to ride in if you don't have your angle held just right. It is not forgiving in any way, but I also felt that it didn't cut the molybdenum stainless of this knife nearly as fast as I expected. So while it is not forgiving, I don't feel like it eats metal so fast that a blade will lose too much metal if I make a mistake. After breaking it in, it feels a little better. The 600 side definitely feels nicer from the start. After the carving knife, both sides are quite usable with what seems like a minimal learning curve. After the carving knife, I put my Kobito to the plate and got a pretty good edge very quickly.

I have only tried it once so far, and the knife was already perfectly shaped. I need to see how it does after if becomes dull, but I think it will work. I think I may prefer continuous diamond for this knife, so I may relegate this SK11 to flattening stones or a field stone and get a credit card sized plate as mentioned before. Either way, the SK11 will get used one way or another. For $28, I am pleased.

As for the Kobito, I feel it cut the blade very fast. I wasn't confident trying to microbevel on this 150/600. It's just too rough to make any nice results at the precision needed. I think I'll look for a finer diamond credit card or pocket sharpener to try that on. In the meantime, I will try using my Smith's 325 when I have a little more time.

The big question I had in the beginning about if the 150/600 would be comparable to similar grits of sandpaper, I think, is answered. I think the diamond cuts very comparable to the paper, but is much easier to use. It's cleaner, simpler and more consistent. Like I said, I didn't expect this SK11 to be the right plate from the beginning, but I think it works as proof of concept for using diamond on this knife. I have a lot of testing I will need to make to decide exactly what sharpener to use, but I think I have a good start here.

Thanks everyone for the advice. I will report back soon with an update or any other questions.
 
Okay, I've already decided that I don't like the SK11 for sharpening. After work, I decided to play on it a bit more. I can't get good results on it with a blade that is large enough to run over the edge. I looked closely with a naked eye and it looks like the diamond coating and possibly the substrate itself has a lip on the edge. I can't be sure, but it sure looks like the edge has a raised lip, whether it be the coating or the plate itself. I think it's eating into my edges. I tried flattening my King with it and that seemed to be okay, but even using the 600 grit on the 1000 King left very visible scratches. I am assuming it is from the rough lip. Hard to tell if this plate is flat or not, all I have is a piece of granite countertop to test. It seems like there is a little wobble on the granite, but hard to see if there is a raised edge. If the edge has a lip on it, that might explain the deep scratches.

I tried to get a really nice edge on that cheap old kitchen knife and found that I couldn't get a good edge until I resorted to my King KDS. The SK11 did a fine job of reprofiling, but I couldn't get much further on it no matter how long I spent on it.

Anyway, now I'm thinking about looking at something like a Spyderco bench stone or maybe a Shapton Glass to test. I don't want to to buy a full set of grits of anything unless I can test one out. Since I can't trust the SK11 to lap my stones, I am wondering if I should try buying an Atoma as I planned before for lapping my King and also as a shop stone or field stone. Along with that, maybe look for something like a Spyderco or Shapton Glass to go from Atoma 400 up to 1000 or 2000 at the highest.

To sum it up, I am thinking Atoma 400 as a coarse stone and also for flattening my other stones. I may or may not keep the SK11 150/600 if I determine it is defective. I would follow the Atoma with something like a Shapton Glass 1K or Spyderco comparable to a 1K grit. I haven't done enough comparison research to see if the progressions would work well. Any ideas?
 
It's been a few weeks, I figured I would post an update. My sharpening technique has changed quite a bit, for all my knives, not just my work knife. The SK11 did seem to have a small area of raised diamond or metal on the edge that is a defect. I just returned it to Amazon yesterday and will order a replacement right away. I have been using it in the meantime, carefully avoiding that edge, just to see if I liked it or not. I have found that I don't love it, but for removing metal fast, it is a lot more convenient than any other option. Basically, for coarse work, I'm just saying I prefer the maintenance free diamond vs sandpaper or other stones that need flatenning or dressing. This particular one, because it is under $30 is great because I can abuse it and replace it inexpensively. So, since this stone was going to be exchanged anyway, I did abuse it. I found that it stands up to abuse of sharpening hard and cutting at 90 degrees if necessary. That's on the 150 grit. The 600 side I didn't really use much because I also got a DMT fine bench stone, which cuts comparatively quickly, but cleaner. The other two items I bought to try were a couple of Sharpmaker rods, medium and fine.

I sharpened the dullest knives I own and a few kitchen knives of family members to try out all my new stones. What I found was that the knives I went all the way to Spyderco fine with, I didn't like. Kitchen knives didn't slice tomatoes well and pocket knives lacked aggressively cutting toothy edges. My work knife, while holding a good edge also suffered from lack of slicing due to the highly polished edge. It would just slide on some leathers I tried cutting. So for my work knife, I am only using the DMT fine and stopping there. I haven't played with microbevels or anything yet, because I haven't been doing enough cutting in the past couple weeks to test much.

So for work, I am pretty much just using the DMT fine. For my standard kitchen knives, I am using the SK11 150 for coarse work on really dull knives, followed by the DMT fine and finishing on the Spyderco medium. I have one recurved vanadium carving knife, which I would normally sharpen on my narrow diamond or a rounded off edge of the King KDS, but to try out new options only, I dusted off an old Eze-Lap diamond rod I haven't used in years. It's a model M, I think it's about equivalent to a DMT fine, followed by the Spyderco medium. Basically, I am able to sharpen everything I own with the SK11, Eze-Lap model M, DMT fine bench stone and Spyderco Sharpmaker medium rod. It all fits into a nice little pouch and is portable if necessary. I'll probably end up buying a credit card sized DMT fine for work and everything else will be for personal use.

I was going to buy a spyderco bench stone, but never having tried it before, I opted for the triangle rods because they're inexpensive. I'm glad I did that because I would have been disappointed if I shelled out cash for a Spyderco fine that I would never use. I may still buy a Spyderco medium bench stone, but for now I made a little holder that works really well. I made this little holder so that it can hold the stone with a flat edge or a corner facing up. Even though the surface is tiny, I use it just like a bench stone, so I don't have to change the way I hold my blades for sharpening between any of my stones. Here is a picture of the holder, shown with the fine stone, but I will probably never use it again. I'll just swap the medium back and forth between the two positions like you would in a Sharpmaker.

That's about it. Thanks to all for the advice here. Seems the best thing to do was just buy a little bit of everything and see what works. I am set with my work knife and now I have a whole new repertoire for all my sharpening. Finally, no more soaking waterstones unless I really want to use the King, which I still love, but is quickly becoming obsolete! I'm sure I'll be trying some more options in the future, but I'm happy for now.


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