Hello Team,
Sorry that I've missed the conversation. Busy.
At conference I had a full classroom session plus a demonstration, and that was not enough time for anything but a brief introduction. The method is new, the joinery is new, and the layout methods are new. At least, I've never seen this before in my 30 years of working with big wood.
First, a few comments on philosophy and my life. For those who think that all wood should be either square or round -- that's a rather small idea. The TFG members who I know, and who I work with, don't see it that way. I choose to work with logs because I love the look of naturally-shaped, smooth, tapered, hand-drawknifed trees. To 'neck' a beautiful, naked, natural log down to a square timber at the joinery is against my religion. I won't be discussing my religion in any further posts. No need to comment on the superiority of square since 2x4’s are square. And it’s quite easy to make strong buildings out of them. So, it is obvious to me that the 'square' idea is not the best idea to be found in timber framing. I think your best idea is more likely to be the 'big wood' idea, and the traditional joinery idea.
Sometimes I use a scriber to transfer the natural contours of one log onto another natural log. Log walls are built that way. But for structural assemblies, it’s difficult to make scribed joints strong. Not impossible, but difficult. But the second problem is that the initial super-tight fits of scribed joints and notches suffer unless we can use gravity and shrinkage to help us keep them tight. The corner notches of log walls get the benefits of gravity, compression, and shrinkage, and these keep our corner joints tight over time. But we don't get all those benefits in the joints of, say, a roof truss made of natural logs. So, using only scribed joinery for space-frames like trusses, or bents, is not a good idea.
My new joinery is not scribed, but it does appear to be a scribed joint because the surface contours of the two logs intersect cleanly, as scribed joints do. My new joint shrinks together, and stays tight over time. It also has big, flat, bearing and shear surfaces totally hidden inside . . . and the engineers tell me they like that. Ed Levin was my co-presenter at the Vermont conference, and Mack Magee at the log builder's conference— maybe Mack can answer engineering questions in this thread?
Each log gets 4 chalklines, and at both ends they get 'cross-hairs' connecting the lines. In a truss, the 2 chalklines that are in the plane of the truss are snapped so they divide log diameter in half at the joints. These sorts of chalklines will be familiar to some of you. But, the 2 chalklines that are in the horizontal plane on each log, are snapped so they go through the thickest part of the log at the joints. (If I used machined logs, then these 2 horizontal lines would be the same as the ‘thickest part,’ but since the logs are naturally-shaped we need to reference off the ‘thickest part.’) You can think of ‘thickest part’ as being the greatest diameter (but actually it’s the longest chord length). This horizontal chalkline is a new kind of chalkline.
Where log meets log, both logs should have close to the same diameter. The closer the two diameters match, the better the joint looks when it’s finished. Here’s why: When two cylinders of equal diameter intersect at their midpoint axes, the joint surfaces are made of two flat planes. (The edges where the two cylinders meet are not straight, they are hyperbolas.) Equal diameters (chord lengths) is the key to good looks. And of course, the interior, flat bearing surfaces are easy to cut (because they are not coped).
If two cylinders have unequal diameters where they are joined, then you get a complex curve in three dimensions -- and if you want the joint to look good, then it really has to be scribed to make the surfaces of the two cylinders meet happily (and that's how boilermakers weld these type of joints). Again, this is why I am not using logs of unequal diameters (at each joint). Of course, the logs are tapered, so their diameters vary at each truss joint. It is easy for log builders to find logs with equal diameters at each of the joints because we have a lot of logs in inventory. This lack of choice will be a hurdle to timber framers. If you try my method to join an 11" log to a 12 -1/2" log you will be very unhappy with the result.
The ‘vertical’ chalklines, in the finished and installed truss, are in a single plane, and this plane is plumb. The ‘horizontal’ chalklines, when viewed in elevation in the finished and installed truss, are perfect right triangles, and the pitched chalklines of the top chords are at the roof pitch. The horizontal chalklines meet at points on the surface of the logs (which is the 'hinge' of each joint, where the two internal flat surfaces meet).
We will be building one of my trusses at the ILBA conference on Vancouver Island, in a hands-on course March 26-27, 2014.
www.LogAssociation.org I’ll be publishing a booklet on the method, and maybe an article in Timber Framing—Ken and I have talked about it. But, it's still new, and I want to use it more before I get it into print.
I do not regularly scan these forums, so I apologize to you in advance for my future slow responses.
