hello all
crowns in timbers--something that has to be dealt with as they appear throughout a timberframe project whether it happens now or 200 years ago--here is my version for what it is worth.
Remember that timbers didn't just instantly appear back then (before saw mills) but were laboriously created using hewing axes by good and bad craftsmen, and sometimes hurriedly time being of an essence.
What I am getting at here is that 3\16 of an inch is not much to worry about, the rough hewn timber could have an inch or more variation as it came to you the framer.
I agree with Daiku 3\16 on an 8by8 will not yield or straighten out you need to snap the line straight, and place your seating straight!!!
Now on a 8by8 48 feet long it will straighten out under its own weight so you work acordingly when you snap the line. Every timber that has crowned from waiting to be used by the framer will need to be assesed for its position and eventual use. On a 48 foot timber it may be necessary to hold the line up, or snap from the centre to the end, knowing full well that it will straighten out when it is inserted in to its position on the day of the raising, This has been my experience for what it is worth, and worked well for us. Twisting is another problem that has to be dealt with, but the experienced framer takes all in stride,, good luck
NH

Thanks again folks for all the replies. I think the diversity of replies/opinions make this site great.

I have decided to go with framing as if the crown is not present, that is laying out the insets and rafter seats without using the chalk line. I will temporarily secure the middle post to the sill by nailing a board between them then I will draw bore the middle post at the plate connection. The boarding on the shed will be vertical. As an experiment I suspended the plate between two sawhorses for about 2 weeks. The result was (without using a micrometer) that the crown went from 3/16" to 1/8" with the timber sagging under its own weight. I measured the crown (actually bow) by stretching a string across the bow. I placed the bowed face vertical so that sag in the string would not be a factor.

Amateur and having fun timber framing...Norm Hart