Hi Chris, We have been in touch before in regards to this wonderful triangle. I just found this discussion group and thought I would introduce this subject for discussion. I have been working, on and off, on trying to master the layout and, more importantly, the understanding of the layout as it relates to the koh-ko-gen and the splayed stool. The ultimate goal, of course is to use this knowledge to fully understand the hip rafter layout as it applies to the Japanese roof. So if this is something you would like to tackle let me know and I will post a few questions that I have. As the saying goes, a picture is worth a thousands words, and because this site does not seem to allow for drawings, we may have to come up with some way to post drawings. Hope this finds you well, David

Hi David,

nice to hear from you and glad to hear you are still pursuing your study of koh-ko-gen. Feel free to post anything you want, and I will do my best to help you out.

If you are currently receiving the TF Journal, there is a series on koh-ko-gen that has just started. The first article came out in the December issue, and the second will be out in March or so. There will be 5 parts to the series or more, and it will progress from hoppers, to splayed-leg stools/tables, to hip rafter layout, and perhaps beyond. I intend to coverthe topic pretty thoroughly.

But meanwhile, please fire away with any questions or comments you might have. Keep up the study!

Regards,

Chris

Hi Chris, I did get the Timber Frame Journal article and it made a good sense based on what I have been able to figure out from my own studies. Now as to the splayed stool... what has me a bit stumped is figuring out the lengths of the stretchers. Let's say that the slope in elevation is 3:10, the bottom of the seat is 1 sun from the floor and the top of the stretchers are 4 sun from the floor. I am assuming that centerlines are used but since the legs are sloping in 2 directions and they have been backed I am not sure how to calculate all the appropriate lengths and from what reference point to lay it all out correctly.I would like to be able to figure it out using the sashigane, ie. layout of the mortices, lengths of the stretchers,length of the legs, etc.
Also it has become very apparent ,that in laying out the joinery ,that any small error becomes a big error when putting the 4 sided stool together. As an example: the top and bottom shoulders of the stretchers as they connect with the leg ( using the same 3:10 slope) have an angle that is .8621:10. When using the sashigane to lay this out and since .8621 is such a small number it is pretty easy to be a bit off and if the stretchers are long the cumulative error grows and becomes really obvious when putting the stool together. The same with shaping the legs to be backed. Any thoughts on how to check these angles. How are things on the East Coast? Aren't those winters something? David

Thanks for the questions David. I'm going to suppose that you meant that the bottom of the seat is 10 sun from the floor (you wrote "1 sun") and the stretchers are 4 sun.
You are right that the stretchers have a 0.862043/10 angle for top and bottom shoulder cuts. The side cuts are chuh-koh koh-bai, which is 2.8734/10 in this case.
The single most critical thing in getting the sawhorse/stool to go together well is to get the backing cuts on the posts/legs just dead nuts on the money. If you do that, then the rest is relatively trouble free. I suggest developing the backing cut drawing on a sheet of paper such that you can expand the post section size to 3-5x larger than actual. That way you can set a transfer bevel or bevel gage to the drawing directly and accurately. A good choice for processing the backing cuts is to use a purpose-built sled in a stationary planer.
You are right that some of the angles get a bit fine and it can be easy to allow small errors to creep in. This is a tough project to pull off cleanly! The tan-gen shoulder cuts on the stretchers are not so bad - the tough ones to execute accurately are the cuts for top and bottom of the mortises for the stretchers, which are, in this case, sloped 0.2372 in 10.
Anyway, getting the lengths of the stretchers is easy, because once the posts are backed the inside plane of each post is square to its neighbor. Since the stretchers - nuki - are in plane with the common slope, the length is figured using the average slope only. That is, take the distance of the top outer arris of the nuki down from the bottom of the seat - seems like it is 6 sun in this example, in elevation view, and perfom a simple calculation of the length of hypotenuse, starting with the distance between post insides where they meet the underside of the seat. For example, if the top arris of the stretcher is 6 sun below the top, with a slope of 3/10, and the legs meet the top with a 10 sun space between then the amount to add to each end of the stretcher is 6 x 0.3 = 1.8. A total length for the nuki, along the top outer arris then is 10 + (1.8 x 2) = 13.6.
Anyway, I hope my clumsy explanation hasn't puzzled you too much. The article I am working on for the TF Journal right now is on the stool/sawhorse form, and will detail all the steps. Ya just gotta wait until March or so. Of course, in the meantime, fire away.
By the way, I'm back up in B.C. for the next three moths, teaching timber framing at the College of the Rockies. From what I gather, New England had had a fairly mild winter.

Chris

David:
If you can scan your drawing or create a screen capture photo of it then you can post it here.
In order for this bulletin board to post a photo, the photo has to be someplace where the board can access it.
I recently found a site called photobucket. It's at www.photobucket.com
It is a free photo hosting site.
Create an account and upload your pictures there.
Then when you've got your picture uploaded go to the photo and highlight the third tag down the img tag. Copy it and then past this img tag into the body of each post where you want it.
Then the photo of the drawing will be posted here as long as it's still available at the photobucket site.
Hope this helps.
Jim Rogers

Thanks Chris, This gives some fuel for thought. I should have an editor. You are correct in the height of the bottom of the seat. 10 sun or 1 shaku. I'll continue to play around with the layout. The bottom and top of the mortices on the legs are not layed out square to the sides but rather sloped .2372 in 10. This is due to the fact that the legs are backed. Correct?
Hope you are enjoying B.C. and teaching. Do you cover this layout technique during your 3 month course?
Thanks again, David

David,

you are correct that the adjustment in cut angle is the result of backing the legs. The important thing with such a slight angle is to make sure you slope it the right way. It's easy to lay it out upside down.
The class I have here is great and the student's are really motivated, but I've been pretty swamped for my first three weeks here and haven't had much opportunity to lift my head and look around town yet. Hopefully this weekend will give me some time to do that. The weather is milder than Ianticipated for this region in January.
I won't be covering the Koh-ko-gen method in this three month course, but it might happen in the future.
By the way, you may be interested in a pair of courses slated for the Heartwood School in May and June in which this method will be explored in detail. We're planning to make a simplified splay-posted bell tower.