Monday, June 29, 2015

Koshikake Kamatsugi Fail

I'm 42 minutes late chilean time, the wood split with the last hammer blows, and a migraine is starting.

First bad idea, leave the joint for the last day.

Second mistake... well, everything else. I didn't take pictures, didn't document the process and didn't finish on time.

At least I blog it to not break all of the rules.

I'm gonna sleep, get something for the migraine, and try it again tomorrow morning.

It was ca 2 hours wasted. It was a 35mm wide piece of rauli I had laying around, the small size didn't help either. I did try to think a la Jason and cut as slowly as possible and see the saw as small little knives or plough planes. Kinda helps. And my favourite saw is dull, I need to make a vice.

See you tomorrow.

EDIT: I made this today for the second try of the joint.

 A 9mm wide stick. I call it sashi, since it's half a sashigane. Maybe just sash since it's also 9mm and not 15.

Here was my attempt to make the tapper. As I banged more later, I managed to break the right side of the neck in the female side.

This is how I lay out the head with the sash. 

Start with the centre line and a perpendicular to that. 
 Then put the sash and mark one side
 Make the line and move the sash to the other side
 Then mark the line and two vertical more at "a" distance from each. 2a = d (width of the piece)
 Put the sash one side touching the upper line and the top of the mortice, and the other side touching the same line at the origin of the mortice.

 Trace that outer line and that's the side of the head
Repeat with the other side. 
And you have a hammer head. 
My sash was 9mm since my timber was 2in and not 3. How did you guys get the slope for the head?

To cut the mortice you saw along the channel first, if you use an azebiki you can go quite deep. Then you chisel the channel out, and the sides of the head are pared away. I need to get myself some decent clamps and start using paring blocks. A real sashiagane and a bottom cleaning chisel are in the list of stuff to bring from Germany next time.


  1. What is it about this joint that makes it difficult? I had the same problems with too tight a fit, banging it with a heavy hammer. It would have split had the pine not been so forgiving. I also noticed that you made the tip of the goose head the same width as the neck, which was something I wondered about. It definitely makes more sense to have them the same width and then only need use one chisel for cutting the female side of the joint. How did you gauge the depth of the mortising? Did you consider adding the taper to the back of the goose neck for the wedging effect?

  2. This one was far too small for the taper. I "kinda" did it by eye only and a very small angle.

    Today I made it again in pine 2"x2" or so, and cut the taper with the saw. Paring the end grain of this radiata pine was horrible, and it broke there when I was trying the fit and taking it out again. I was too lazy to go downstairs for the marking gauge (a veritas) that I could have used, but I just marked the chisel with my finger and checked it with the line in the outside.

    By then I was hammering the thing 3 or 4 times in and out, without realising the error was precisely in the tapper.

    The mortice in pine was mostly done with the azebiki, and then one chisel for the whole channel and the edges of the hammer head pared to the line. That part was actually ok.

    The tip of the goose neck comes from the lay out. I put my "sashi" (half a sashigane, ie, a stick of 15mm -- which in my case was 9mm for the smaller timber size --) and mark the channel, one sashigane each side. Then you put the sashigane as in the picture and that gives you the angle, I found it beautiful. Got a picture and may make a post if you didn't get the explanation, I suspect is not so clear.

    For me at least, there are two things that make this difficult. One, I don't know how tight needs to be. Like I lack that intuition. Second, I cannot keep the focus during the whole joint and start to make mistakes more and more as time passes...

    Ok, I blog about the lay out now, at least to feel I accomplished something.

    I'm making this joint a third time, not tomorrow that need to go to the city but before the end of the week.

  3. In soft wood like pine or red cedar, you can use a lightweight (4-8 oz.) hammer, with a round or domed face to go over the mating (tapering) faces of the male piece, "killing the wood" though it doesn’t really hurt it, because once the joint is together, the wood fibres expand again, locking the parts together in one welded piece. Stay away from the edge that meets the face.

    Also, use the sliding Inside/Outside callipers to gage respective parts.

    As soon as you have an intuitive sense of the woods limitations, these two tips come more into play - they are no substitute for fracking up - a prerequisite for getting and refining the intuitive sense. It's a two way dialogue and the wood is the master. How could it be otherwise?

  4. That is how I did my layout as well, 'cept I was too lazy to make your "sashi", instead relying on proportional measurements. For me, measuring is too often a source of error, so marking sticks, gauge blocks, and story sticks are always my best option. Foolish of me, but this time I got lucky.

    As a beginner, I am striving first to get a perfect piston fit between the two parts. I am REALLY working hard to ensure that all of my surfaces are first as flat/true as I can make them. I look at every plane as an individual project. Slow, but my accuracy is getting much better, as is my speed. When I concentrate on speed first, my skills seem to just get worse.

    IF I could get the perfect piston fit....then I plan to cut the line a little fat, then "kill the wood". Someday....

    Our practice sessions are working! It is very helpful to me, watching you guys do your layout. I need to be more diligent about my documentation. Great work!

  5. I'm really loving this, if it weren't because of you guys I would have stopped at the first fail. This keeps me trying to improve, learning. Shall we start with the third Jason?

    Wood is an implacable master, reflects too much of myself and my laziness. Let's keep on learning.

    1. I would happily choose the next joint....shall we start again on Monday? A little time to lick our wounds?

    2. Monday sounds good. I should pour some alcohol on them too.

  6. Yes, Monday and back at it with what you choose Jason. Save the alcohol for celebration of well cut joints.