6th Apr 2017, 06:29 PM #1
Fixing Deformed Ashi (Legs) on a Kanna-ba (Plane Blade) Ura
I am posting this as a kind of a WIP for other who have a similar problem. I make no claims to the legitimacy of my solution and if you undertake to replicate this process I will not be held responsible for the consequences.
One of the most common things you find with second hand kana-ba is that the blade is often in poor condition. One of the most common defects is that the ashi (legs - the flat area down either side of the ura edge) has become overly broad.This is a problem because it makes sharpening far more difficult because the hard large flat surface area that needs to be maintained. I have been toying with ideas of how I could reshape the ashi on a kanna-ba.
I have seen a process where a chuck of a very course stone is used to hand grind a defective ura into shape. I however do not have the patients to spend 3 hours rubbing a tiny stone backwards and forwards.
Now this is what the ura looked like before, I started.
I bought a cheap small aluminium oxide wheel the kind people use in a Dremel, I however fitted it to my drill press. I then set my VFD to a very slow speed and set about grinding with care the ashi that was excessive.After about 5 minutes of freehand work I ground away a good amount of the flat part of the ashi. This is what it looks like not very pretty, but thats not the point at the moment.
Then I tried to introduce a gentle curve into the ura with the very edges being high and the middle being of the ura being low.
I then took the kanna-ba to the medium stone just to see how effective the grinding of the ashi was. In all honesty it took me three attempts and a total of 15 minutes to lightly grind away enough of the excess ashi. However I was using a light touch and a slow grinding speed. I was initial concerned that this process my produce a large amount of heat, however the blade never felt warm to the touch.
I then F-clamped the kanna-ba to a workhorse, I then mounted a small flap wheel in a hand drill - this was easer to work / refine the whole back evenly then using the drill press. With in a minute I was able to refine the errant grind marks into something half agreeable in appearance. Then it was a quick process to establish the flat ura on a medium stone. After sharpening this is what I ended up with with before and after photos.
As you can see that ashi are now much closer to what you see in a new blade. While not perfect the ashi I think it looks better, and the reduction in the time take to sharpen the blade is significant.
Thoughts, opinions, outrage?
7th Apr 2017, 02:40 PM #2Senior Member
- Join Date
- Mar 2010
Looks good Thumbsucker. Nice job.
I have wanted to do the same thing and came up with a slightly different solution.
I've seen photos of blacksmiths using enormous diameter wheels to do this so wondered how I could make or simulate such a wheel.
I have a cheap linisher like the one below so took a piece of 25 mm thick board, cut it to the width of the belt and marked a 750 mm radius on the side, then planed down the top to the radius.
Used double sided tape to attach the board to the linisher bed. Now the belt runs over top of the radiused board and produces a section of 1.5 m diameter wheel. I also bought some graphite rub strip and adhered it to the top of the board to lessen the friction. Works well but I don't have any photos as the moment. Hope my explanation is understandable.
7th Apr 2017, 06:12 PM #3
Gauge - I think I get it, pretty smart. Your method would produce a more uniform radius ura, mine is more by feel and eye.
I have seen that giant wheel as well very impressive, I thought that its much like those massive sandstone wheels once common in the west for grinding. Just the rotation axis is different.
I want to reiterator to anyone reading this, the reduction of the ashi has significantly improved this blades sharp-ability and performance. If you have a kanna-ba with a malformed ashi, I highly recommend you find a way to trim its legs.
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