Learning Scribe Rule

 We spent all of today working on the first layup, as its known in these parts.  This is one truss that will make up one side of the bridge.  Layup included establishing the top and bottom chords (beams) in their respective relationships (parallel and centered), measuring for the vertical posts, and laying those in their respective places.  With everything carefully shimmed into level and plumb, or as close as you can get with semi green rough sawn lumber, we began marking for the joints.

When I was preparing for this trip, I searched high and low for information on timber frame layout, and all I could find was that there are two primary ways: square rule and scribe rule.  I know that square rule focuses on the idealized timber within the actual timber and that scribe rule deals with laying out all of the timbers and marking them in relation to one another.  I also know that many modern frames use a combination of the two techniques for different components and applications.  What I could not find on the internet was anything more useful or detailed than what I've written above, so I was unable to even learn the theory behind these techniques.

Now that I am here, learning some of the fundamentals of scribe rule, I see why that is.  This is really difficult stuff to convey in words without being able to physically perform the operations and demonstrate it in real time.  I think that a well made video could do wonders for learning the basics, or even more advanced techniques, but you really need to be able to see and hear what is going on for it to make sense.

The main tools we used were a variation on the plumb line and a pair of dividers, as well as a pencil and a small ruler.
 

The frame in lay up, with the bottom (in the picture) posts not yet aligned.

Will demonstrating the technique.