Sorry about the link not working. not sure what to do about that, except provide the actual address where the pic is stored:
https://picasaweb.google.com/104943063435486564254/December62012#5818993359399316450I have long found this forum very awkward to use for attaching pictures.
As to your comments Don, well, I see things a bit differently. Yes, you've drawn me out of my cave.
Pegs are not stiff connections, first of all. The draw bore is helpful in keeping the connection firmly together, in the case of a post and a beam say, during shrinkage and/or seasonal movement. I don't think it's purpose is primarily to stiffen the connection, since pegs are inherently flexible. That said, draw-boring does place a joint in tension, however that tension is going to vary - the peg needs to behave elastically to a certain extent. If the beam shrinks, the tension on the peg is going to ease.
Peg size and number, along with structural arrangement, timber size and joint detailing are significant factors that affect how much tension might be in a joint, however no pegged connection can resist much tension anyhow. The pegs will flex, and at a certain point
relais will give or the peg will break.
'Draw-boring', to my way of thinking, is more about the principle of off-setting the peg hole in mortise and tenon so that the peg has to elastically bend around as it is driven through. I don't take the word 'boring' to only mean with a drill or auger. 'Bore' simply means to make a hole. Whether the peg mortise is round or square doesn't affect that off-setting mechanism, so making an argument that the technique was not 'feasible' in Japan until augers came along is not convincing in my view. Also, to say the joint used in Japan is 'not equivalent' to the one used in western work is misleading - they are alike in principle and only differ in respect to the shape of the mortise for the peg. I would say they are equivalent.
The argument about "
Japanese construction is in principle about the right amount of flexibility, I mean a flexible joint and one highly tensioned don't go well together" is not winning me over. I think too much is made of that 'flexibility' by some writers, and it is a bit simplistic to characterize an entire framing system, especially one with great diversity in methods, in that manner. Diagonal bracing has been employed in wall systems in Japan for 150 years, as one counter-point. Connections which suffer tension in Japanese framing, like western framing, are typically reinforced with metal. Case in point would be angled wall bracing, which the Japanese do not peg but tie in place with metal and hide in the wall. Pegging diagonal braces is problematic, as you probably know.
I might add that diagonally braced systems also suffer from flexure, both by lateral deformation of the timbers by the braces, and insufficient stiffness at the pegged connections.
Many scarf connections, like
kanawa-tsugi, or
sao-tsugi (rod mortise and tenon) joints, involve driving in a wedge or pin to drive the end grain bearing surfaces of each joint half in opposite directions, placing the joint in a degree of tension. How does this square with your assertion that tension in the connections is somehow incompatible with Japanese framing practices?
It would be correct to say, I think, that Japanese framing is primarily a system of framing components to bear compression loads rather than tension. That's a logical way to employ solid wood in a structure, is it not?
I also might point out that after your argument that creating tension in a joint is somehow alien to Japanese carpentry practice, you then state that a 15mm peg having a relatively small cross section - aren't you therefore saying that such a connection would be less capable of creating tension? It seems like a contradiction.
I can add that 15 mm pegs are fairly standard in Japanese framing because the structural parts to which they associate have been fairly standardized in most respects for the past 100 years or so - 105mm or 120mm post sections, for instance. In much the same way, western framing might most often be done with 8"x8" posts and 3/4" pegs. It doesn't mean that custom sizes and larger/smaller pegs are not employed in other situations.
I think the offset, draw-bored connection has some advantages when done with a square peg mortise rather than a round one. And it is still done, often enough, simply by chiseling work.
