Hi Don & Jim,
I am sorry about the delay in replying to the draw bore question. This topic has probably been done to death elsewhere on this forum but yes indeed draw boring is well proven to be a very early practice that predates the founding of the American Colonies at least by 2 or 3 centuries and probably much more.
The important thing to recognise from and engineering standpoint is that drawbores are employed in conjunction with tapered pegs (or is that pins) and so when a peg is being driven it pulls the joint together up the inclined slope of the peg. Driving home the peg is thus somewhat of a "musical" or resistance based process. Knowing when to stop driving is therefore very much an experience based affair in order to prevent tenon relish pop.
Old draw bore pegs that are removed exhibit parallel deformation over the span of the tenon though whether this happens straight away or over prolongued periods of time is difficult to say.
One other understated factor that comes into play is mortice "slop". Most american timber framers employ engineers squares to ensure perfectly parallel and straight sided mortices but examination of old frames reveals that mortices tend to be more bellmouthed starting at say 1.25" opening up to 2" at the bottom with all the load being taken on the tenon shoulders and peg. This means that the tapered peg is actually unsupported over a short length either side of the tenon and thus is able to deform elastically rather than fail in shear. I have a wonderful photos of this practice taken in Laurie Smith's cruck framed house in Wales (Gwernfyda - dd 1552) where a tie beam was partially sawn through to create less of a step over and into an inserted upper chamber. See Fig 24 in TF 70 [Dec 2003].
I shall risk being a little controversial here in stating that I think that the current "tight" fitting parallel mortice side practice is probably techically misguided and certainly less forgiving.
Regards
Ken Hume
