Ko-Ganna Restoration

Hello and welcome to my blog!  In this post I will detail the process of restoring a single iron small kanna referred to as a ‘ko-ganna’.  This plane is a vintage market find that had been used very little or not at all.  Unfortunately some modifications and mishandling happened along the way and this small plane required complete restoration before it could be put back into use.

Before we delve into this plane, I’d like to make mention that the Japan Society, located in NYC, will be hosting a talk by Douglas Brooks.  Douglas Brooks is a much admired fellow craftsman who pursues the Japanese art of traditional wooden boat building.  I have this on my Exhibitions and Events page.

17 DouglasBrooks-BoatBuilder-singlepg


I hope that readers will attend the event, I will make the effort to attend myself and very much look forward to visiting the Japan Society.

Now I will return to the feature of this post, the Ko-ganna.  This plane might strike the casual user as being unworthy of any real effort in restoration, however the dai presented some traits that suggested otherwise.  The plane had been setup for use as a single iron plane.  Often users will simply remove their chip breaker and pin, then declare the plane a single iron (I’m guilty of this all the same).  However, a true single iron plane has a wear angle specifically set for that purpose and this plane had such a setup.  I would not expect that to be typical of a low quality plane.

As I inspected the plane, what struck me initially were hammer marks worked into the face of the iron.  Normally this area is left untouched and damage is seen around the atama, which is the top of the iron.  Upon discussing this with a friend of mine, the owner of this plane, he mentioned that in his opinion it was likely that someone attempted to remove the iron from the dai by whacking it with a metal hammer on its face.   This made good sense to me as to why those marks would be there.


My first step in repairing this plane, and restoring some dignity to this tool, was to apply a hammered finish to the blade, disguising the damage done to it.  I worked the blade until a uniform finish was created, then filed the outside perimeter with a very fine file to restore the outside edge.  Finally I applied a blackening agent to the iron.  Luckily the maker’s mark was left in-tact by the original user and so I made certain to leave it intact as well.


With the hammer marks now disguised, I turned my attention to the bevel.  The bevel had been badly rounded over and so it needed to be ground flat and returned to a more typical angle.  I brought it to 25 degrees, I will show a photo of the bevel toward the end of this post.  To my relief the lamination appeared to been made by a smith and so indicated that this plane may well be worth the effort being put forth.  A bevel that is so badly rounded over needed to be worked out prior to ura-dashi, normally the opposite is true however removing such a large amount of iron can sometimes cause the back to cup and so only requiring ura-dashi again after the work is completed. I left the bevel at 1000 grit knowing that I would be working on it twice.

I put the blade aside and turned my attention to the dai, or plane body.  The dai was severely cupped and bowed to a point at which I’ve never seen from normal movement of a small plane.  Likely it was stored in a manner that aggravated it’s normal seasonal movement.  I began flattening the dai, by hand, and taking notice of the high spots, lucky enough the mouth was lowest point and so nearly untouched from flattening.  Lucky as it were, but unfortunately the mouth had been opened by someone intent on setting up the plane but had given up prior to seating the blade thankfully.

Next I resurfaced the remaining six sides.  The end grain had been roughly worked by the maker and the ‘dai-gashira’ or front (the back on a western plane) left square and without chamfers.  In nicely crafted dai, it is typically for the top edge of the dai-gashira to be rounded over using a special plane to allow it to endure hammering.  So much work was required that simply refreshing the plane entirely was my chosen course of action.  I removed the original patina, but those who use Japanese planes know that the patina will return very quickly.

The dai turns out to be a beautiful piece of oak, masame orientation showing straight grain front to back and a wonderful fan of medullary rays.  As mentioned above, further inspection revealed that the dai was originally made to suit a single iron.  An area of the dai known as the koppa-gashi was setup as such.


The koppa-gashi would be known as the “wear” on a western plane.  The wear angle is adjusted to suit the planes intended setup and use.  In this case the wear angle was very low.  This was intriguing to me, at first glance I thought little of this plane.  However, the mouth had been opened up so far that the effect of a low koppa-gashi would be unrealized in use.  This had to be attended to as I wanted to realize the original maker’s intention for this plane.  The course of action is to cut out an insert known as ‘kuchi-ire’, or a dovetailed key.

Normally a sliding dovetail is tapered along its width, and done so because it makes the cutout very easy.  In this case it must be tapered along its thickness as tapering along the width will split the dai as the key is inserted.

I cut out a key, then transferred marks onto my dai in preparation for cutout of the kamagi, or throat as it would be known in a western plane.


I chopped the center out as one would do when cutting the bed of the plane, working my chisel with bevel down and riding the bevel as I removed material.  The area was then smoothed by paring action and my attention then turned to the dovetail shaped side grooves.   These grooves are pared, working from the mouth of the plane to the outside edge, this allows the chisel to work with the grain of the wood.

The key’s wedge shape allows it to be seated tightly, additionally it is glued in with hide glue.  The key can be kept long and adjusted along with the dia, allowing the user to set the key lower and trim it off with each sole flattening.  I opted to trim it flush being that this is a light use plane.


Previously I have used macassar ebony for the keys, however I’ve moved away from that to lighter colored woods.  I set my plane depth by viewing the blade protrusion while siting down the sole of the plane, this process is made more difficult by use of a dark colored wood such as ebony.  I chose quarter sawn red oak for this key.


The mouth appears almost impossibly tight when viewed from the bottom of the plane. However this is exactly how tight the mouth needs to be in order to function properly in the form of a smoothing plane.


When viewed from above, it becomes clear that there is clearance for the shaving to pass through.  This view should also make clear exactly what I mean by a low wear angle.


For comparison, this is the wear angle typically of a plane used with a chip breaker.  My preference for normal use is a plane with a chip breaker.


The mouth of this plane appears nearly as tight when viewed from below, but obviously provides more clearance when sited through from above.


I’ve yet to sharpen the ko-ganna to any real degree, having left the back setup for another time, and yet, it was able to take a clean shaving and show the purpose of a tight set mouth and low angle wear.  The shaving is moving upward along the blade before pitching forward, this is similar but not quite as effective as a chip breaker which will send the shaving over the blade.  Possibly a keen edge will narrow the gap closer still.


I hope that you have enjoyed following along with this post, and I look forward to your comments.  The next post will return to shoji making as I have nearly completed the project and it nears installation.


  1. Nice job, Brian! Looks like the plane was worth the effort.

    I take it you have installed “keys” on other planes in ebony. You commented that they were more difficult to do. Why is that?

    I would think that the superior wear-resistance of a wood like ebony at the mouth would be worth the extra trouble.

    I have several planes with “keys.” The one I like the best is an Usui Kengo blade in a So dai. It has a bubinga key, held in place with two screws in recessed slots. The screws bothered me at first until I had to actually lower the key to compensate for a worn mouth. The screws made the whole process so much easier. So left the key projecting out of the well perhaps 5/16″ above the top surface of the dai to allow for a lot of adjustment. This too was an excellent idea. In fact, the projecting key is really handy to grip!


    Stan Covington
    1. Thanks Stan! I was amazed by this little plane. I find it more difficult to sight down the sole of a plane with an ebony key since my eye will confuse the thin black line of the key for the protruding blade when the blade is set very faintly like for kez. Otherwise, in normal use it’s not a distraction.
      That’s interesting as I had debating a bubinga key, it seems like a nice wood to use for this purpose, being not especially dark but certainly very hard. I noticed that a number of my small planes have this key made up in red oak so that nudged me toward the oak. Are the screws right into the wood or did he use threaded inserts?
      For my planes that will really see some mileage I left the insert sticking out, I agree it’s a handy grip.
      Good to hear from you! I was very glad to see your name pop up in the replies this morning!

      1. Good point about the visibility of the blade’s projection with a dark wood key. I must admit, my Usui plane is a bit more difficult to adjust even with the red of bubinga, but by orienting the dai to get the light right, it works anyway.

        The screws are fine-thread machine screws fitting directly into the white oak dai. I assume So (Ito-san) drilled and tapped the holes just like they were going into metal. At his grain orientation and with Japanese white oak, these kind of screws work just fine so long as they are longer than what would normally be needed to develop the required tensile force in metal.

        I was skeptical when I was first told about using machine screws in this way, but I found it works very well indeed. Ones does have to be very gentle with the tap, and clean the sawdust out frequently as it is easy to break out the thread otherwise.


        Stan Covington
      2. Thanks Stan, I think I’ll give that method a try on the next one of these. A little easier to adjust than hide glue. I also tried rice glue like what was suggested in Odate’s book and found that the wedge would not hold. Thanks again!

  2. Hi Brian,

    You certainly sensed a diamond in the rough regarding this little plane! It had been for sale at the local flea market for some time and I had often passed on it, knowing next to nothing about it. Western tools I am conversant and comfortable with; Japanese, less so. Only after meeting you and seeing your knowledge and passion regarding Japanese tools, did I consider its purchase. Even though less than $20, you have shown it to be a tool worthy of restoration. I appreciate the detailed steps you’ve outlined, so, along with your other postings regarding blade and plane tuning, if I ever try this sort of rehabbing myself, I have a great foundation from which to work.


  3. Very nice work on the kanna and the article. The photo sequence is very informative.

    I am curious how you textured the blade. Did you use some sort of peening hammer? Also, what was the blackening agent you used?

    I also have a kanna dai with a red oak key that is held in place by two recessed screws. I cannot quite make out the dai makers stamp. The screws are in the wood, not in threaded inserts. The blade is an “Idaten”, by Shogo Tanaka.

    David Wong
    1. Thank you David! Good to hear from you. I used the funate genno that I modified for ura-dashi. The blackening agent is called ‘Brass Black’ but oddly enough it works just fine on iron.
      Interesting, I’ve seen the insert on Tsunesaburo planes but I’m surprised to hear they’re actually much more commonly used. How do you like the Shogo Tanaka blade?

  4. The “Idaten” blade is maybe my most used. It is a 55mm that I use like a block plane. Capable of fine shavings, shooting, and rough work. I don’t have the mouth set narrow, so I have not had need to use the insert key. The key is 9/16 inch proud of the top surface of the dai. I agree with Stan that it does provide an additional convenient grip.

    David Wong
    1. Sounds like a nice plane, I find some of my small planes being used similarly, especially those with the protruding key. I have one Tanaka plane now, it’s in super white 1 and I’ve been putting some time on it, a really wonderful blade so far.

  5. Hi, Brian! Hope you are well. I’ve been looking for some time for info about setting up a block plane and just stumbled onto this thread. My question is about preparing the dai. To me it seems that a two or three touch point sole will not provide enough of a flat area touching the work piece. Any guidance that you can give will be appreciated.


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