Mo,
great questions. what is the best way to deal with bowed and crowned timber using the square rule, both from the edge and from the line.
Here is some of what we do.
Situation: bowed bent girt or tie beam with joists joining both sides
Dilemma: do you snap a line on the beam or try to straighten the timber?
fix: lay out the joist pockets from the edge and then use the joists (and perhaps a truck strap) to straighten the girt.
Situation: crowned bent girt or tie beam with joists coming in.
dilemma: hump in your floor.
fix: If it is too much crown, plane it back into tolerance.
situation: bowed wall girt or plate.
dilemma: nobody likes a crooked wall.
fix: plane it straight if it is out of tolerance and can't be replaced.
situation: bowed collar with king post joining it or similar situation.
dilemma: the faces of the timbers won't be flush if you are using snapline square rule.
fix: Best way to deal with it is to either plane the faces flush after assembly or lay the mortise and tenon out from the edge even when snapping lines to keep the faces flush. There is a certain amount you can fudge that before you mess up your shoulders.
You mention resorting to mill rule to avoid these problems, but you have to deal with crowned and bowed sticks that are planed, too. Maybe it's just us, but we rarely get any perfect pieces of wood.
I think that all of these solutions remind us that it is expensive in labor to build with crooked, twisted, or otherwise irregular wood. Some times that is the nature of the project, such as when using hewn timber or reclaimed timber.
I would love to hear how others deal with these issues.
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