Wednesday, July 15, 2015

Project Mayhem #3 "I don't know what it's called..." part 2

Turns out this type of tenon joint is called a " Yatoi-hozo", thanks Sebastian!


Funny too, because in a previous post where I was ranting about shachi-sen in the comment section, one of Chris Hall's posts that I referenced as a good source for information on layout went into great detail about the etymology of the name and kanji symbol. I was so enraptured by the joinery, I guess that I wasn't reading that closely.

OK, back to work.

I find it much easier to drill out as much of as possible first, then clean up using the chisels.


I've been waiting to use this chisel for a couple of years but never got around to making it pretty. The numbers on the handle are from the Japanese architecture school where this was used originally. Funny thing.... It was obvious thst they didn't use chisels very much, as the chisel had never been sharpened properly and it still had evidence of that weird thick oily crap that they put on tools to preserve them from rust. The kasura ring on the handle has seen plenty of use, though. Maybe it never needed sharpening, the steel is so good? I bought this on eBay for $25, figuring that a trade school probably knew more about good quality Japanese tools than I did. We were both right, it's a great chisel!

I cut the mortice too deep. This seems to be something that I need to work on. Maybe a mortice depth gauge will be the subject of an upcoming post. No real harm, it's just that it equates to wasted effort and it feels careless to not be as precise as possible.

The walls of the mortice are nice and vertical at least.

Though the inside doesn't look so nice. I should sharpen, but I'm still trying to rush, get finished with this thing before dark. I draw the lines inside the mortice, to define the slope of the dovetail.




Finally, an excuse to pull my "point of a sword" knife out of storage!




This is the perfect tool for shaving the inner walls of these oddly shaped mortices.



And here's where I left off for the night.

It's getting dark and starting to rain.






The next morning, I cut the stock for the rod tenon/Yatoi hozo.

That saw of Sebastian's sure cuts a straight line.








I have been working to better developed my eye. Sawing skills too, but when I make any cut, I pare or plane the cut surface by eye, until it looks good to me....THEN I check against the square.

This is another one of those stupid little things that seems to be paying large dividends. My sawing might not be perfect, but my eye accuracy is getting really good. It ends up saving lots of time really, as you don't need to use a square as often.




I place the tenon into the mortice, then mark to measure depth.




Draw lines.





I place the tenon exactly as I wish it to finish out, then mark for the shachi-sen retaining pins.




In cutting the trench for the pins, I want to taper things just a bit, to help draw the tenon tighter into the mortice.

I taper about 1.5 mm, but a little more might have been better. 2-2.5mm maybe?







Ha! Too loose!

Almost 1/8"..... Good god!



You can fix nearly everything using glue and wood shavings.

I used 4 thick shavings that I found on the ground.





Do some laundry while I wait for the glue to dry.




About 1/64" was added to the thickness. It doesn't seem like much, but it's enough.








I chose 1" width.




But because the shachi-sen are trapezoidal in shape, the stock that I need should be at least 1-1/8".





Time to assemble.



Oh yeah!



Here is where all of my "skill" practice comes to term. All surfaces are trued by chisel or plane, verified by eye, I cut to the line if I can, then before I offer the pieces up, I check again. Can I make it more perfect?


Whenever I have been dissatisfied with the outcome of nearly any project, it has usually been because I cut a corner somewhere, didn't check or verify something, or was just in a hurry. It's funny to me that I just am getting the hang of this now but, working with care and focus is SOOO much faster.


Anyways, one time, no trial fitting really. Don't get me wrong, it's not perfect, but it's decent.

There is a slight gap at the shoulder. I wonder how well these shachi-sen will draw up the joint?




All that fuss over measuring the width of the shachi-sen, and I just eyeball it, haha.


I use my cutting gauge. I should set it a touch deeper, but oh well. These are great tools to know about. They are dirt simple, make one.




As my compatriots have advised, I cut the angles for the trapezoidal shachi-sen by eye.

It's a perfect fit. Too perfect, actually, because I had intended to taper them so that they would draw the joint tighter, haha.




Shachi-sen v.2.

Mystery wood from the dump. Hard, smooth and looks like ham.


Mmmmm, ham!



This time I remember to leave the stock about 1/8" fat (I guess that I'm still thinking about ham, haha).




The stock is long enough to provide materials for both pins, mirror images of each other, which is very handy. That means that I can place a mark that divides the piece in two, then taper each end. That probably doesn't make much sense, but if you think of turning the shachi-sen stock into a long, blunt diamond shape, you would be close.


I tapered the stock enough to fit into the mortice.




Maybe a little much, as the pins sunk nearly home using only firm hand pressure.




The small hammer drove the pins in fully. Both bottomed out, so they should've been a touch wider.




Even so, the joint pulled together perfectly.





Even the ugly side of the joint. Remember when I said that I only surfaced and measured from two faces?

It worked.



Pretty darn good.





So, here we have it, the Yatoi-hozo joint, Project Mayhem #3, my first real success.

The others were adequate, but not satisfying. This one felt right.


It's solid.


  1. Jason,

    as far as the terminology goes, yatoi-hozo is one name. The other name for this joint is written upon the picture you shared at the top of the post, "引き独鈷車知栓", hiki-dokko-shachi sen. Also can be called "寄蟻引独鈷", yose-ari hiki-dokko.

    You did a nice job on that joint.


  2. Thanks for your encouragement Chris!

    Your comment is timely in particular as I'm currently staying up late nights, making my biannual visit to your series thread, "X- marks the spot".

    Your explanations and examples of the exercise, brought throught to the 2-D expansion of the individual components is particularly helpful as I try to wrap my mind around that pesky Japanese splayed rafter construction that I'm admiring.

    If anyone out there wants to see some really nice examples of this joint, I encourage you to do a Google Image search using Chris's thoughtfully provided kanji of alternate names for this joinery.



    For those of us who are interested in this sort of thing, learning the terminology is one of the biggest hurdles to discovery. Having the kanji gives a huge boost, good for hours of exploration down the rabbit hole, haha.

    Thank you yet again!

    1. Darn link formatting didn't work.....whoops, my apologies.


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