Thursday, April 28, 2011

Tying Joint 3D Model

Here are several views of the latest iteration of the 3D model I'm developing of the tying joint used in the Hawkins house frame. This joint is used to fasten each post to its respective tie-beam end, forming the bents, and then subsequently tie the bents themselves together via the front and back top plates, thus forming the basic, standing frame of the house.

The image below shows a typical post top, which is joined to its tie-beam via a tiesel tenon. I still need to determine if the tenon actually extends all the way back to the (non-tapered) end of the post, or if it stops just short of the post end (this is one of the least accessible areas of the post, as it faces the exterior sheathing):



The next image shows the corresponding tie-beam end. A large 3x8x9 shoulder cut out of the bottom of the tie-beam supports the 6x9 plate, which in turn has a mortise that accomodates the 2x8x9 tenon projecting horizontally from the end of the tie-beam, just above the shoulder. Plate and tie-beam are drawn together via a single 1 1/2" peg, pounded in from above. There is also a smaller hole to accomodate the end of the peg securing the rafter foot where it is stepped on to the plate. A mortise cut into the bottom of the shoulder, and extending partly into the tie-beam just beyond the shoulder, accomodates the post's tenon:



Note that, if the post tenon actually does indeed extend all the way to the back of the post, then this mortise is most likely opened at the end of the shoulder. I haven't determined yet if this is actually the case, but this is how I've modeled it for now. I also need to determine if the mortise is blind or open on top. Again, all this is difficult to discern, because this part of the joint is almost completely inaccessible to nondestructive probes.

The next image shows the tie-beam end, as viewed from below. There is a pronounced, adzed reduction in the bottom of the tie-beam, which, on average, extends about 9" inward from the inside edge of the mortise, and is about 1/2" deep:



Here is the tie-beam end, as it would appear facing head-on. An odd characteristic of the mortise, visible from this perspective, is that the blind part of the mortise, just beyond the shoulder, extends upwards an additional 1 3/4", despite the fact that the tenon itself has been measured as only 2 3/4" in length at this end. There is no obvious reason why the blind part of the mortise is cut much deeper than what the tenon actually requires:



Below is yet one more image of the tie-beam end, as viewed along its length:



And here's a photo of an actual Hawkins house tie-beam and post joined together. The plate, of course, is just beyond the wall and ceiling, so not visible in this photo:



The layout of this tying joint might very well be a vernacular design of the Second or Third Period of the New Haven Colony. It's a much simpler geometry than the classic English tying joint found in most First Period homes, and suggests that the Hawkins house might've been constructed later than claimed.

I've never seen this style of joint diagrammed in any of the early timber frame surveys I've studied. Several of my colleagues in the Timber Framers Guild's TTRAG told me they're not familiar with it either, and suggested it might very well be a design that originated in my local area. As I'd mentioned in a previous posting, the Reverend Richard Mansfield House, less than ten miles aways, employs an almost identical tying joint in its bent system.

6 comments:

AlexandraFunFit said...

Well, the exact specs of your joint are a bit beyond me, but your house certainly seems like a fun project. I can't wait to find out what you probe next. I'm still awaiting the birthing room probes! And however did you get up high enough to take that picture of your ceiling? Did you stand on some fossilized corn cobs from your attic? BTW, is a mortise a type of fruitcake?
P.S. It would seem you are getting closer to solving the mystery of just when your home was built. That is quite exciting.

John Poole said...

Alexandra,

A mortise is a kind of deli sandwich, made with rye bread, mustard, pastrami (optional), swiss cheese, ....

Hahaha! Thanks for your comment. Yes, I had to stand multiple times on an old trestle table to get that high. Good thing it could withstand all the weight! As for the birthing room walls, I still need to master the fine art of wall sonogramography, as these walls are quite old, and I am not willing to poke around them with borescopes, etc. But if there are any old shoes to be found, that's where they'll be (of course, I'll probably just find more desiccated corn cobs!)

~John

West Coast John Poole said...

I wonder if you were to color each component, e.g. red, white, & blue, and then use X-ray to show all three intermeshed. Not quite as grand as a fireworks display, but could be intriguing.

John Poole said...

Hey cuz!

That's exactly my intent. Not sure if I'll do it using color, patterns, or wire-frame, but I do intend to show the internals of the joints when drawn together.

Also, I just started experimenting with a library of Ruby extensions that support timber frame components, so we'll see how that goes, too...

Thanks for stopping by!
- East Coast Poole

Craig Chartier said...

Just wanted to let you know that we have identified this exact same joint at the Taylor-Bray Farm in Yarmouth, MA. We believe that the joint was originally used in the c. 1640 Richard Taylor house. The beam that it is attached to is painted black and white (black at the butt where it joins the post and white along its length). We are currently awaiting dendro dates from it.

John Poole said...

Thanks very much for that valuable piece of information, Craig! Please feel free to post additional comments here with your dendro findings, if you want to. I'll likewise be doing dendro analysis on this frame, but nothing is scheduled yet.

The closest cataloged examples I've found so far are in Sobon's "Historic American Timber Joinery": p.11, Fig. 11 (albeit, plate and tie-beam are reversed); p.15, Figs. 25-27; and the triple bypass on p.16, Fig. 30, only this joint has a much simpler post/tie-beam connection than the triple by-pass, of course.

Thanks again for your comment!
~John