Each joint has two joinery planes. If we have 3 points on the surface of a natural log then those 3 points determine one joinery plane. Another layout method requires only 2 points plus the slope of the joinery plane (2 points and an angle determines a plane, as does 3 points). Which method is preferred depends on how fast you want to work, whether your logs are roundish in section, or are oval/lumpy/weird, and how many jigs you want to own.
Two of the points that we need for both layout methods are easy to establish: these 2 'easy' points will always be located on the horizontal chalklines. And, if you could connect these two points with a line through the log, then that line will be normal (90 degrees) to the plane described by the vertical chalklines. (You cannot actually connect these two 'easy' points until after the joint has been cut, of course, there's wood in the way!) I call these 2 easy points the 'hinge' points -- because the two joinery planes of each joint appear to hinge here. There are always 2, and only 2, hinge-points per joint.
For the 2-point-and-angle method, once we have the 2 hinge points, we need the angle. Each joinery plane bisects its involved angle. I love how simple this is; and the engineers like that the bearing surfaces are always exactly the Hankinson angle they want for grain slope. An example: two logs to be joined to each other at 45° (eg the top chord of a 12:12 truss joined to the bottom chord). The joinery planes for this joint will 22.5° (half of 45°) and 67.5° (half of 135°). These angles are measured from the horizontal chalklines of each log. A piece of MDF can be positioned like a horse collar over the log, and it is lined up with the 2 hinge points, and then is set at the desired angle. (The MDF in the photos is not a template: it has no markings on it, and the ellipse was roughly cut only so it would fit over the log. It is a reference plane, not a template.) Trace from the MDF onto the log’s surface. That’s your cut-line for this first joinery plane. Re-position the MDF through the hinge points and at the other angle you need for this joint. Then repeat on the other log that will join this one (one is male, and one female, of course). All measurements (span, height, length of pieces, etc) are made along the horizontal chalklines. That is, the length from one joint to the joint at the other end of a log is a measurement from hinge-point to hinge-point, and the required length is found by trig (or proportions, pythag, or etc). All the joinery can be laid out on all the logs before anything is cut, the logs are never positioned over each other, are never leveled lengthwise, there is no lofting, and no lines are snapped on the floor.
I should mention that snapping accurate chalklines on natural logs is not as quick and easy as it might appear. There are unique skills to putting chalklines onto logs. The line must be aimed, not just pulled back and let ‘er rip, but that’s another topic. Just a heads-up that you need skill in the basics to get good results here.
A much faster way to lay out the 2-points-and-angle can be viewed in my short video here:
http://youtu.be/hO6w3njpzqYIn the vid, ‘HP’ is hinge point—you can see that the jig really does hinge on these two points, and then is locked at the required angle. The 2-point-and-angle layout produces joinery planes that are always 90° to each other, so you set the jig once and mark both joinery planes. (It’s great the way the geometry works out. I wasn’t expecting this when I first started working on it. But when layout, engineering, & cutting all click like this, I knew I’d found something sweet.) If you’re keeping score-- from the example above, you’ll see that 22.5° plus 67.5° = 90°. For accuracy, I use large MDF triangles cut on a table saw to the angles I need, not that tiny digital protractor. And my jig, made of “8020” parts, has been slightly improved since I made the video last summer. The truss in the still photos was built by students in my 2013 Univ of Alaska course. They had no timber frame experience, and had been working with logs less than 3-weeks. This was the first-ever truss built using my method and joint, and I think they did a pretty good job with it.
Now, for the 3-point-layout, which is the method I demo’d for the TFG, we use the 2 hinge-points (identical to the HP’s used in the 2-point-and angle method) but we also need to determine where on the vertical chalkline the surfaces of the two logs will intersect after they have been joined—we need ‘surface points.’ If the logs are not very circular in section, or have substantial sweep or bumps, then the 3-point method can produce a more attractive joint than the 2-point-and-angle method. (Not a better fitting joint, a joint that has log surfaces that are more “fair”.) To find where the log surfaces will intersect on the vertical chalklines, you could position the two logs over each other and then use a scriber, or a line-projecting laser, or a plumb-bob. But accurately positioning 1-ton logs over each other is a time-consuming, hair-tearing-out hassle. And it has to be repeated for every pair of logs you will be connecting. So I came up with a portable story-board (foam core) to find the surface intersection points. No log has to be leveled lengthwise. The story board is pinned to the HP of one of the logs and then that log’s surface is projected onto it, and drawn. Next, pin the story board to the HP of the mating log, and project it’s surface and draw it. The log surface projections will cross each other on the story-board and these are the points we are looking for. They are easily transferred from the storyboard back onto the logs.
This gives us 3 known points marked on the log for each joinery plane: 2 hinge points plus 1 surface-point. I recommend you use the MDF horse collar, sling it over the log so it goes through the 3 points, and then trace it, score the line, and cut. Someone truly skilled with a flexy rule can join the 3 points without using the MDF horse collar, but I don’t think many timber framers have that skill yet—it takes practice to get accuracy.
The 3-point method and portable storyboard produces lofting benefits and lofting results . . . without lofting. The logs to be joined can be sitting in different corners of the yard, or even in different hemispheres, if you don’t mind mailing the portable story board. I decided to demonstrate this technique at Burlington because I know that some timber framers loft, and I figured that they might want to consider the portable storyboard idea for their own purposes. The portable storyboard solves lofting problems that come with timbers (and logs) that are heavy, long, awkward, unstable, numerous, or distant from each other. You just carry the information on the storyboard from timber to timber, without having to carry (or position) any timbers. It could even be used to 'loft' pieces that cannot be moved—say if one piece is already part of a structure.
Please note that 3-point layout produces joinery planes that are probably not at 90° to each other in a joint. This isn’t a problem: I’m just saying that only the 2-point-and-angle layout produce joints that are necessarily 90°. With the 3-point method I never even measure the angles of the joinery planes, because I don’t need that information. The joints are equally tight with both layout methods.