Project Mayhem Japanese joinery challenge #4 Katasage ari

 

 

Joinery practice #4, chosen by Steven of "The twin maples"

 

A great joint, the "Katasage ari", taken from the FANTASTIC book "Wood joints in classical Japanese architecture".

 

 

 

Download a free copy here....

https://fabiap.files.wordpress.com/2011/01/wood-joints-in-classical-japanese-architecture.pdf

before it disappears. It's now out of print, and it is seriously good, having not only a great sampling of the more common joinery used, but also a little bit of where the particular joint is used and often the reason *why* a joint was chosen. This book was written by two guys, one an old school Japanese carpenter, trained nearly 100 years ago, the other an engineer and architect. This book is just great.

Thanks so much Steven, for showing me this book!

It's raining again, go figure. Have I mentioned that it rains a lot here?

 

Rather than begin with some nicely squared stock, this time I'm going for something different. This joint seems like one of those eminently practical ones, although not overly complex. My thought is that something like this joint might actually have some good applications in the real world, like, something that I could be using repeatedly in the very near future. I've been looking for some good, simple de-mountable joinery to use for building temporary or transportable shelter, and this seems a likely prospect.

 

And....I want to chop some wood, so I think that this one.....this one will be cut from the roughest stock available.

 

 

The second that the rain stops. I run to the wood pile and grab a couple of likely looking chunks.

I cut a length of Guava, and also split off a section of a rotten old Ohia that I've been messing with.

 

 

Rough out, using the hatchet....

 

...then plane the minimum amount of surface flat, just the area that needs to receive the mortice.

 

 

 

See how jagged and rough the Ohia is?

The sumisashi marks this wet, rough wood with no complaints at all. I wouldn't dare trying this using my oh-so-fancy $10 felt tip fine line drawing pen, but with this simple bamboo pen....no problem. I am such a convert! It seemed messy and kind of scary, but in reality it's just fun, and actually quite clean. The ink only seeps into the wood the barest amount, and completely disappears with 1-2 passes of the plane. In comparison, a pencil might require twice as much planing to erase a mistake in layout, most notable in softwoods. It's not for everyone, I know, but Holy Crap, I'm in love!

 

So here's where I screw up. This joint is so simple, I should've honoured that intent. Instead, I felt that the tenoned piece should be shouldered, to offer a more solid base and to assure that everything stays square. That, and I didn't want to plane this wood down any more than was necessary. What I should've done, was to just rough the thing to size using the axe, then call it good.

Anyway, the layout is getting to be more of an enjoyable part of the experience. I credit the ink, haha.

The purplish wood is the Ohia, one of the few native Hawaiian trees, also one of the most dense to be found anywhere. This particular piece is still wet, having been from an ancient deadfall tree, maybe 400 years old, but portions of the trunk are still usable though much of the trunk is rotten. The technical briefs that I've read about the attributes and uses of this wood say that it can be cut and machined using the same type of tooling that you would use when processing frozen lumber. Yikes!

 

Actually, when wet, I found that it cuts surprisingly nicely, using Sebastian's awesome saw, the big 300mm ryoba. Dry Ohia is another matter.

 

 

When I decided to cut the joint using non-square stock, I also figured that I would just kinda eyeball the angles too, as you can't mark the side face of a round log. Not well, at least. If you look to the background, you can see that I was quite liberal in my interpretation of the tenon design here. This might be considered a bastard cousin to the Katasage ari joint that I was SUPOSED to cut, haha.

And no, it's not that the color balance of my camera is off, it's that the guava that I'm using is stained a funky yellow color from bug and bacterial staining. Normally it would show a creamy sapwood with purplish brown heartwood.

 

 

For starters, I cut the mortice to fit the tenon. I ignore the area where the wedge goes, for now. I cut the joint haunched (I guess that's what it's called) with a 1/2" deep area for the haunched area, then the rest of the tenon at full depth. I cut that stuff first, but didn't bother taking pictures. The undercut area that accommodates the angled half-dovetailed part I cut by eye out of necessity, but I was able to use a "Gabe D™" bevel gauge to give some confirmation.

After drilling and cutting most of the waste from the mortice, I need to cut the wedge before I can finish. I start out with a chunk of Guava.

 

 

Plane two parallel faces until the width matches the mortice.

 

 

I saw the wedging surface at a likely looking angle. Nope, didn't measure, but then, I didn't need to.

 

 

 

I guestimate how deeply I want the wedge to fit into the mortice, then use that spot on the wedge itself to determine how much more material to remove. Essentially, set it where you want it, then mark it.

 

 

 

The wedge itself makes a handy bevel gauge.

 

 

 

 

First fit didn't require much trimming at all, but then, it was far from being a piston fit. Hammering in the wedge was a trip.

This joint is surprisingly solid!

 

 

Being who I am, I had to get the fit just the tiniest bit finer, one of the shoulders was 1/16" off. And....this is meant to be a de-mountable joint, so that's part of the deal, right?

I had to drill a hole into the wedge to get a better grip, then had to do some fairly vigorous tapping (using my new Ohia maul) to get the wedge to pop free. This wet wood is very grippy! If a person intended this joint to be de-mountable on a regular basis, you might consider a mortice in the wedge itself, its own tapered wedge, just to break it free from the body of the joint. A hole drilled through the joint, that goes through opposite the wedge would be another option, if the hole wouldn't be visible in the finished work. That way you could just poke a screwdriver through the hole, popping the wedge out with ease, a better solution than this, I think.

One other point. 

In practicing these joints for the first time, my inclination is to try to "improve" them in some way. "It would be stronger, if I just...", that sort of thing. This is a perfect example of the original being good enough. As drawn in the book's diagram, this joint is fast, easy, and strong. Cutting this guy took maybe 2 hours, but should've taken 45 minutes, at least for a beginner like me. I made the joint slightly stronger perhaps, but if ultimate strength was a concern, there are a multitude of other joints to choose from that would be better suited for this application. I constantly fight myself in this way. 

 

 

So....Awesome fun joint,and very useful too. Next time round, I will cut this guy as the simple thing that it should be. I was horribly late on this challenge, as I was finishing up the long awaited awning frames for the shed.

Simple simple stuff, but it shows a certain flair, I suppose (actually rather embarrassed, but....). Of course, as soon as I was done, the most amazing book came to my attention, one that had numerous examples of much more elegant and/or practical ways to build this particular structure.

 

That's for later.

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