I am trying to design spline joints into a purlin post frame, but I do not know exactly how these joints are typically proportioned to the timbers. For instance: in addition to the top plate, there will be lower longitudinal connecting girts that are 6" x 8" joining an 8" x 8" post. How thick should the spline be?, how deep should it extend into the girts vertically? and how deep horizontally as well? Also how many pegs ? and what diameter would you use? also does the spline get pegged to the post as well?I also notice that splines seem to be exposed below the joint, is this necessary? if so, how much should it extend(1-2"?) below the joint? As you can see I have a lot of questions. I think this is a really perfect joint to use in this specific case, but I do not have the historic examples and general guidelines to design from. Perhaps more importantly, with continuous purlin posts, the "tie" beams (8" x 10") also specify the spline connection to the 8" x 8" purlin posts. In which case, what dimensions and pegging would be designed there? Anyone with knowledge on spline joinery would be helpful. Thanks tb

Ted Benson's first book has some spline drawings, as does his plan in the guild red book.
I see a spline that is 1 1/2 x 4 x 16, with no pegs in the post and two pegs in each girt, and 1 1/2 reveal on the bottom.
It's not neccessary to expose the spline below the girt/post, but this would make a stronger spline with less removed from the girts.

this sounds a little short to me, I would like to see 12-16" on either side of the post, and the plan looks like that, just the description of the spline calls it 1.5x4x16.... also I would use a little deeper spline, with at least 3" up into the girt, 4 might be better depending on what else is going on at that spot.

the spline should be hardwood of some kind. 1" pegs are fine, I would set the spline at least 1.5" from the reference face into the post and girts

Picture please if possible. I'm trying to visualize this and a pic would really help. Tanks!

Here's a pic of a similar spline set-up from the Holder Bros. blog...the spline is the dark wood visible at the bottom of the intersection.

Nice work Holder Bros., by the way.

http://picasaweb.google.com/holderbros1980/PhotoArchive#5271981992826887362

I like to have three pegs on each side and off set them so they are not in the same grain line. I usually have 12" past the post with a 3,6,9 pull 1 1/2 off the top and bottom edge alternating.

Would the spline be 1.5 to 2 inches thick like a typical tennon?

I'm also assuming that the spline depicted is offset to one side of the post so as to give clearance for a possible mortice coming in perpendicular to the spline, but coming close to the spline?

1.5 thick spline should be lots provided it is hardwood, set 1.5 into the timber should be ok in 8 inch stuff. The second pic in my last post shows a plan view.

So, it looks like nothing is attached/pegged to the post. How is the spline installed? Is it set and pinned onto one of the beams, then fed through the mortise? Or it it all installed without holes, then pulled with straps and come alongs then both sides drilled and pinned? I would then assume it may be slightly draw bored?