First page of the glassstone archive.

Japanese Skiving Knife Repair

Posted by is9582 on January 11, 2018 with No Commentsas , , , , , , , , , , ,

I have a really beautiful Japanese skiving knife that my daughter and son-in-law bought for me, while in Japan a couple of years ago.

 

The bevel side of the blade on the Japanese skiving knife.

The bevel side of the blade (already sharpened) on the Japanese skiving knife.

 

The back side of the blade on the Japanese skiving knife.

The back side of the blade (already sharpened) on the Japanese skiving knife. Wooden stop at left (next to the corner of the blade) is used to set blade projection for this tool, when in the Kell honing guide.

 

I was using it to thin some leather from a piece where it would blend with a joint, and I noticed it wasn’t sliding through the leather like it had when I got it. My eyes aren’t what they once were, so I looked at the knife’s cutting edge under some magnification, and what I saw just blew me away! The edge was chipped something terribly!

 

This is the cutting edge of my skiving knife, before repairing the chipping.

This is the cutting edge of my skiving knife, before repairing the chipping.

 

I’m the only one who has ever used this skiving knife and I always handle my tools very carefully, and it has never fallen from the workbench or come in contact with anything other than leather. I even made a leather sheath for this knife when I received it, so it would be protected.

 

The Japanese skiving knife in it's leather sheath I made especially for it.

The Japanese skiving knife in it’s leather sheath I made especially for it.

 

It is possible that the steel used in this skiving knife is not flawed at all, even though it would seem at first glance that the heat treatment possibly left the blade too brittle. This isn’t uncommon in the blade making world, as the outside (what I might call a skin, for lack of better terms) can be a bit too far towards the brittle side, but once this skin is removed, the remaining body of the blade is both hard and resilient.

 

Ok, so how the heck can I fix this, without spending hours at the water stones, and without using up half a stone? Now this is going to sound crazy to some, but you hold the cutting edge perpendicular to the 1000-grit water stone, and move the blade down the stone. I know someone is cringing just thinking about doing this to a blade, much less with the damage it will do to some water stones, but stay with me here. This is one of the places that the Shapton Glass Stone series of stones really rock (not that they don’t rock all the time), when you have a narrow tool (something like a 1/16″ chisel or the working the edge of a card scraper), that can plow furrows into your water stone(s). The Glass Stones have a much harder matrix that most water stones I’ve used, and I find they do a better job of withstanding these focused pressure situations, without leaving deep depressions in the stones. Ok, back to the skiving knife… I visually check the knife’s cutting edge after each pass on the water stone, so I don’t waste my time, the water stone or the knife’s steel, and continue until there are no remaining chips on the blade’s edge (not a cutting edge at this point, as this process creates a flat at the edge) of the skiving knife. You may be wondering why I would use this technique, rather than working the bevel as you normally do when sharpening. I find this technique to be much faster and very reliable.

 

The chipping is all removed, and you can also see some of the paths this took on the Shapton Glass Stone in the background.

The chipping is all removed, and you can also see some of the paths this took on the Shapton Glass Stone in the background.

 

Now that the chipping is removed, its time to work the bevel on the 1000-grit, until the created flat at the tip is gone. This will prepare it to be a very sharp blade! This skiving knife has an amazingly acute honing angle, and the handle can get in the way of some honing guides, when trying to work at this low an angle. I decided to use my Kell honing guide, as it could hold the blade for this type angle, even though I found it was just barely able to retain it. What I mean regarding retaining the blade, is the blade would try to pivot ever so slightly during use, even though I had applied recommended pressure with the Kell honing guide. It turns out the back section of the skiving blade has a little taper to it, rather than two parallel edges. I found I had to put strong finger pressure down onto the rear part of the blade, while I was moving the Kell guide and blade up and down the water stones, which kept the blade static. One way to determine if you have actually removed enough steel, so that the back and bevel meet in the perfect “zero radius”, is to hold the blade with the cutting tip facing up towards some lights. If you can see any reflected light from the tip (not the back or the bevel) then you still have a flat on the tip and should continue to remove steel from the bevel. When you reach the point where there is no longer any light reflected back from the cutting tip (and you can feel a small burr all along the edge, from the back of the blade), it is time to shift to your finishing water stone, which should be at least an 8000-grit or higher. I prefer to use my 1000-grit water stone to remove the burr from the back of the blade, as it only takes a couple of swipes, but it really depends on the situation. Now on to the finishing stone, for both the bevel side and then the back.

 

Here I've just finished sharpening the skiving knife on the Norton 8000-grit water stone, and the Kell honing guide is seen to the left of the stone.

Here I’ve just finished sharpening the skiving knife on the Norton 8000-grit water stone, and the Kell honing guide is seen to the left of the stone.

 

You should be left with an amazingly sharp tool! I tested my skiving knife on a piece of leather, and it cut through it like it was going through soft butter. This is a wonderful tool that is back in business!

 

Thank you for reading the article and please let me know if you have any questions or suggestions.

 

Lee Laird

LeeLairdWoodworking@gmail.com

@LeeLairdWoodworking – Instagram

Sharpening – Do I need to go to 30,000 grit?

Posted by is9582 on March 2, 2012 with No Commentsas , , , , , , , , , , , , , , , ,

Like many of you, I sharpen on a very regular basis. I’ve tried most of the different sharpening media that is presently available, along with some that are not so readily found any longer. I’ll share some of the results, and hopefully answer the title question.

When I first got into woodworking, I purchased three King water stones in grits up to 6000. I had decent results, but the lower grit stones dished so quickly that it seemed like I was spending too much time trying to keep them flat. At that point, I didn’t have any diamond stones, with which to quickly flatten the water stones.

Later on, I bought a WorkSharp 3000, thinking it would not only sharpen, but provide rapid repeatable results. Another of the major selling points for me, was the ability to flatten the backs of old chisels, without spending hours at a stone. The highest grit was again 6000. One thing I noticed that seemed to be even more important for the finest grit sheet, was laying the sheet completely flat. Since the grit size is so small, on the fine sheets, a small bubble or leftover residue on the plate can cause uneven honing. One accessory they added, after I “parked” my WorkSharp, is the leather honing wheel. I have not tried this option, but it may offer some of what I perceive as the missing precision, at the final honing process. One caveat to know, is leather will compress, which may not sound like a problem. Depending on the thickness of the leather, the amount of compression can vary, and cause some unwanted results. One such negative result would be a slight rounding over of the tool edge. This may not show itself, until your next sharpening. Put some black marker on the surface you wish to check, out to the very edge. Work the tool in the normal manner, at the grit at which you normally start. After a quick touch to the media, check to see if any of the marker remains, at the very edge. If it does, this indicates the very edge has at minimum, a slight rounding. Since I haven’t personally played with their leather honing wheel, I can’t advise as to its compression factor, but a light touch is suggested. The WorkSharp, in my configuration, provided decent results.

The next sharpening system I purchased was a Tormek T-7. One of the selling points for this system, is it has a large number of accessories that make it possible to sharpen almost anything. For my needs, that part was overkill, since I primarily wanted to quickly and easily sharpen my chisels and plane irons. The T-7’s sharpening wheel has a grit size of 220, which using the provided stone grader, can be modified to act as a 1000 grit. It works well, but as you might imagine, even after going to it’s leather stropping wheel, the tool sharpened was no where near a 6000 grit sharpness. On tools such as turning gouges and the like, the level of sharpness from the T-7 was certainly adequate. Tormek has additional sharpening wheels, of which, one is a 4000 grit Japanese stone. I have not tried this stone, but it is still an option, for those wishing a finer edge, while still using the Tormek. For optimal results, chisels and plane irons still needed, at minimum, some light attention on an 8000 grit stone.

I own both Norton 220/1000 & 4000/8000 water stones, as well as Shapton Glass stones in 1000 & 16000 grits. The Norton stones have a medium matrix, so they both provide new abrasive regularly, but it’s strong enough that they don’t dish as quickly as the King stones. Even with this said, I flatten these stones either between each tool, or after a minute or two of use. This may sound compulsive, but it’s what is required to know you are not unintentionally adding shape to an edge. The Shapton Glass stone series is a ceramic matrix that is quite a bit stronger than the Norton’s matrix. With this, they dish much less quickly, while still sharpening quite rapidly. I still flatten these regularly, but I can probably work a bit longer, before it’s needed. Since they sharpen quickly, it’s unusual to spend more time on a stone, than it can stay flat, other than potentially the 1000 stone. While I don’t use the Shapton stones as regularly, I keep them for sharpening non-flat items such as carving tools. The harder matrix helps them hold up to the tough contact of this type of tool, much better than a softer stone. Both Norton and Shapton water stones, at these grits, provide an extremely sharp tool that I can trust to be razor sharp.

Ok, ok, I haven’t mentioned anything in my kit that is close to a 30000 grit. How can I try to compare tools sharpened via these stones/devices to a tool at 30000 grit, if I don’t actually have a 30000 grit stone? Yeah, that wouldn’t be cool. As it happens, I do actually have a couple of natural Japanese water stones, that are each in the 25000 – 35000 grit range. I have tested both American and German made tool steels as well as Japanese tool steels on these stones. Can I tell the difference? Hmmm, that’s a good question. I really don’t think I can tell much difference in the non-Japanese tools. Once something is razor sharp (e.g. reaching the 8000 grit range), it’s exceedingly hard to feel much difference in the way it interacts with wood, at higher grits. On my best Japanese chisels, I can tell the sharpness is enhanced, even though it isn’t hugely different, as you might find moving from 6000 to 8000 grits. Beyond the sharpening aspect, the natural Japanese water stones leave a different finish on the tools. This is most noticeable on the laminated Japanese tools, although still viewable on almost all tools. With the laminated tools, these water stones leave a different finish on the hardened steel compared to the soft iron. The hardened steel looks almost like a cold mirror, that someone has breathed on, leaving the foggy myst. This is much more pronounced than when sharpening these laminated tools on other stones. Other tools will also take on this non-shiny texture, and strangely, it is still amazingly sharp.

Many people look at a tool’s edge, and if sharp, expect to see a mirrored type of reflection. Just a reminder that shiny does not always equal sharp, especially if the sharpener did not hone at an angle sufficient to reach the very edge. When you sharpen, make sure you raise a burr on the opposite side, so you know you’ve actually reached the edge. Otherwise you may just make something shiny.

Is it necessary to sharpen a tool to 30000 grit? For me, no, but this seems like a more personal question. I think as long as you sharpen to 8000 grit, as a minimum, you’ll have tools that make woodworking what it’s suppose to be. FUN! Go make some shavings.