Joe, I geuss what I meant to say was that... whatever you want to call the line that is the meeting place of the top of the plate and outside vertical side of the plate, this line falls in the plane that is defined by the tops of the rafters. The rafter plate arrangement that Jack uses for the shed is the same that can be found in his historical joinery essay figure 9 (chapter on rafters). If I drop a chalk line along the plate at any location and use it as a reference then the rafter seats will be 3/16" lower/deeper towards the middle of the plate than at the ends due to the crown. I think this will result in the "line" (plate top/side intersection) being above the rafter tops by 3/16" at the middle of the plate.

Norm Hart

Ah yes, the rafters are flush with the top corner of the plate. You are correct then in that you will need to knock the corners off of the plate if it is indeed more than just a rough shed. There are other less desirable solutions ( such as moving the joinery up 3/16", decreasing the bearing, etc.)

Maybee 3/16" crown is nothing to worry about?

My answer is; it's a carpenters choice. Any of the previously mentioned options will work also treating the plate as straight will work as well. First, the crown will be bearly visible. Second, slight mid-span crown looks good but slight sag never. Third, the geometry with the crown is very close to ideal. Assuming otherwise straight and square material and a 12 ft. plate to plate outside distance. With a 3/16 crown, the outside dimension increases to 144.00012 in. The slope of the rafter plate seat deviates from level plate top by .001302 per inch. The ridge will rise by 3/32 and will shift slightly away from crowned plate, amount depending on slope. So in practical terms the deviation of geometry is within normal tolerance of construction.

Norm

I am, and was guessing that you were going through the exercise of cutting this shed, not only to have a great little bldg, but to learn as much as could be realized in the doing…

So I’m going to elaborate on the quick sketch I threw at you before. You may have carried your project to the next phase, even so this aspect of framing can be understood just by playing with ideas.

Go back to the drawing I asked you to create earlier, step over to your problem plate, even if you have it completed. Snap those datums - datums being the lines which describe those two perfectly perpendicular planes of reference which flow through your imperfect timber. And any and every timber for that matter. If you haven’t done this before, e me and I can walk you through the process. For purposes of this exercise simply draw a parallel line 1 ½ “ from the two reference faces > top & outside < of your theoretically perfect 8 X 8.

Now go to your stick, walk a third of the way down, to one of your rafter locales – approaching the apex of your crown but not to the half way point, where wind cancels it ‘self out.- Physically measure the actual distance from the datum to the imperfect surface at all 8 locations – 2 for each of the 4 sides – bring this information to your drawing and connect the dots, You now have a completely accurate representation of the imperfections your timber holds at this location.

For most joinery all you need to do is treat your datum as an 1 ½” offset to draw then create your joint in it’s perfect plane – a ½ “or 1” from theoretical reference or whatever the need demands. Joints which approach their surface a an angle are another matter !

Back to the drawing and the step laps, extend the lines up through the lines you drew which describes the actual surfaces, now measure the distance from the datum and convey this information back to the stick, and so on and so forth.

Like I said youcan know the actual points at which the joints enter and exit the true surface. Yes you can, describe and then cut perfect joinery into any timber no matter how imperfect.

If there is a catch, it is that you must reference the tooling that you use to create these “perfect” joints from those perfect planes ie; you must create a plane parallel to it from which to register your combo/protracter/bevel/what have you.

Best of luck
and
Be your best

Will

Thanks Will and everybody that has responded to my question. Will you are definitely correct that I am in this to learn as much as possible and looking forward to a great building. I have moved on to the next phase. However I have taken the time to understand and go through the exercise you outlined. I find especially interesting the way that joints that approach a surface at an angle (rafter seats etc.) are affected by timber defects. I have gained an apprectiation of this.

Doing my best and loving timber framing...Norm Hart

Here is a shot of Norm's Shed. I guess 3/16" crown in the plate wasn't that much of a problem after all.
Great job Norm!

Way to go, Norm! Lookin' Good.