Saturday, August 9, 2014

Hammer head..... How I battle the forces of inertia!

The new/old kanna has one aspect that I am not thrilled about.

Hammer head.

You can see how the grain of the wrought iron has been distorted. 

Just about every kanna that I've bought has had this condition to one degree or another. When you are a carpenter, you don't carry some special little frou-frou brass hammer for adjusting your plane, you use what's in your hand! That's a steel hammer, ergo.... Hammer head, the mushroomed-over top on the blade. Plastic deformation of metal sounds a bit wordy.

Compounding the choice in kanna blade adjustment devices is the material that the kanna blade is made from. The tool that I want (and sometimes actual get, haha!) is a higher quality plane, and they usually have blades made from wrought iron.

Wrought iron is a great material for kanna blades, because it is soft, so it sharpens easily. Being soft also means that performing ura-dashi (tapping out) on a blade made with wrought iron is MUCH easier, than on a blade made from regular modern soft iron. Ren-tetsu, good for kanna (but not for chisels, maybe).

Wrought iron being soft, and easily deformed, causes the head to smoosh and fold over. I wish that this didn't bother me, as this whole "make pretty" thing is rather silly. This tool works great, as it is. It doesn't need to be pretty. Almost as bad (To me... I'm crazy!) is the way a blade looks when you grind off the folded over part. Then you are left with a misshapen blade, outlined in bright, shiny metal. It draws the eye.

So, I try to hammer the heads back into shape.

Polished tools help. The hammer gets a bit of assistance from an old cold chisel, reshaped and polished. I found it on the side of the road. The idea is to apply force, opposite to what caused the deformation in the first place. The chisel gets underneath, where the hammer won't fit.

Even though the wrought iron is soft, there is only so much that it will tolerate. It would be nice if we could apply heat, but that would draw the temper, ruining the edge holding ability.

The iron may tear, but hopefully it will be a net gain, overall.

It's looking pretty good from the front, back to it's original shape.

Not as nice from the top. Here you can see that the iron has exceeded its threshold of resiliency. Much of this will still need to be filed away. You do what you can.

After filing the nasty parts away, I etch the blade with ferric chloride (PCB etchant), just to get a better look at the grain of the wrought iron.

I love this stuff! Each blade is different, and so beautiful.

The top gets planished to a faceted, hammer finish, then etched, to peek inside.

I didn't want to change the shape anymore than needed, so a little bit of the damage is still there. If I had just used a grinder to remove the distorted metal, I would be left with a flat-top, lopsided kanna blade. This hammering process can preserve much of the iron and come close to regaining the original profile. It does take work.

It isn't apparent from the photos, but the hammered surfaces are actually rather bright. I would like to tone that down, to blend in with the original finish, but this blade doesn't have much original finish, so.....

Birchwood-Casey Super-Blue, gun cold-process bluing liquid to the rescue. You can apply it to small areas, to blend, but the darks might not match. I obviously did everything in sight. Cold bluing is not very durable, and can fade within hours, weeks, whatever. Handling will accelerate the disappearance, but it's easy to reapply.

Something must be in the air today, but the super blue is actually turning blue (often it's black), and I don't really WANT blue, so.......

Rust bluing. We're going old-school!


  1. Jason,
    You sure are a perfectionist. I've never had a blade that was that deformed on top but I did buy a used kanna once that had the top mushroomed some. I almost hate to say it now that you said you don't like the ground-off look, but I used a large coarse file to take the mushroom edge off and bevel the top edge all the way around. It actually turned out looking pretty good and I use a small steel hammer to set these blades so I don't mind a bit of mushrooming.

    I am waiting to see how you deal with that ura that was deformed when someone didn't tap it out but just kept grinding away on the stone. Do you have a sen for a job like that? It would have to be some pretty hard steel to cut the ura face of a kanna blade.

    1. Hi Dave!

      Oh, I've ground them off, too! Roughly filed is how the smiths finish 'em, so your repair would be more in keeping with tradition, I would say. I think that it's fun to try and replicate the original finish, but when I do file work, it just doesn't have that..... Élan? I get too fiddly, fussy I suppose.

      These guys just whip these tools out, no big deal, just a day at the job, and they do the file work hot, using big rasps. I love clean file work, because mine isn't! I get a kick out of seeing an edge finished , using just one pass of the file, and have it be perfect. It's a talent, born of time and practice. You have to do a bunch, to get any good, I suppose.

      I've tried using a carbide scraper to carve out a nasty Beta-ura, but even that didn't work well. I had to apply so much pressure, just to get it to cut, that I didn't have very good control. Carving out the ura has you working right at the cutting edge. I was feeling like it would just take a little slip, and I'd have some major ura-dashi work ahead. I use little die grinder stones or an actual 4-1/2" hand held grinder and a small wheel, but I'm working on making a shield, to make the process less nerve wracking. I've seen pictures of jigs used by a few different hobbyists like me, but I'm still looking for examples of what the pros use. I suppose they just use the big wheels. The urasuki is usually ground after the steel has been hardened anyways, so that's what I'd do. My wife won't let me get a big wheel :'(

      Thanks for checking in!


    2. On yeah, I forgot to mention......

      I cut a 1/2" slice from one of those cheap China diamond sharpening stones. Just the metal face, not the plastic backing, and a regular set of tin ships cut it like butter. The electrodeposited coating was surprisingly durable and well adhered. The small slice can be bent and conformed (to a degree), letting you hand finish the tight areas. Slow, but does the job.


  2. I know this post is 5 years old now, but can you point me in the direction on the jigs you eluded to in your first comment for addressing beta-ura? I’ve spent hours searching in Japanese to learn a lot of interesting things about these tools, but I’ve yet to stumble across anything besides a small corner of jnat, emery powder, or a freehand die grinder for correcting the ura. Thanks


Like all of us, I am figuring this out as I go, so when you see something that is incorrect or flat out wrong (and you will!), let me know. This is a learning process. Real people and names, please. Constructive comments and questions are very welcome, but hate speak/politics are not! Life (get one!) is too short.

Thanks, Jason