3 way post joinery

[bigshow]

I was hoping to use primarily 8x8's in as much of my house as possible, but sitting down and drawing out the joinery...I have found out that i know zero about 3way connections at a post.  4way looks easy enough - 1" housings all around and upper/lower splines.

So, as per my picture.  Is there any way to join timbers all the same size without having a colossally sized post? or is going up in post dimensions the best bet?  Wood is Eastern White Pine - 2" thick x 4 1/2" long tenons should be used.


So, say all are 8x8.
the green is my post obviously, the red - i can see using a spline to join these...but what would i do with the white?
I'm assuming i've answered my question...if i cant make it work..then it wont.  But, this is my first design - and would like any input.


thanks for any responses.

[Jim_Rogers]

Part of the decision depends on the loads being placed on these timbers. Is there any?
If the white one is a floor joist then there isn't much, you maybe able to do an under spline going from red to red and an over tenon on the white, with a good shoulder for the white to sit on.
If the reds are supporting the outer floor boards and the white will hold up the joists then you may have to re-think it all together.
It's very hard to give a specific answer to a special situation without seeing the entire frame and understand the whole thing.

Jim Rogers

[bigshow]

So, I'm thinking i'll have to bump up to 10x10 post in this situation.  So, say i have a 10x10 post, with 3 8x8's tying into it. 



in the image, i have the two 8x8 girts housed (housing not represented in the pic) with a spline.  So, the joist - lets say i do a 1" housing for it - will i still need the tenon to be 4 1/2 long?  or since it has a 1" ledge to sit on, can i shorten the tenon to 3 1/2"?  This piece will be serving as both a joist and tying into another post.

thanks again....

[Jim_Rogers]

Here is the way I see it:



First of all your spline should/could be offset to the outside of the two red pieces, so that it is 2" off the outside, as shown in my drawing.
This will give you more room to make the tenon on the white piece longer, thereby making it stronger.
Then when you create the edge for the white piece to sit on, make it a sloping housing called a "diminished haunch" this will make the joint stronger. Also a standard pegging rule says the peg through the tenon on the white piece should be at lease 1 1/2" off the shoulder of the diminished haunch of the post, and that will give you 4 1/2" from the end of the tenon, which I have drawn in as 6" long and nearly butting up against the spline.
If the spline is low enough you could make the tenon on the white piece longer and make that a through mortise with the tenon going up and over the spline and this will give you more relish for holding in the peg, which you can raise up to be in line with the longer tenon.

From my gallery here is a picture showing just such a joint:



If you need to see larger shots of either of these, send me a private email, by regular email, and I'll send them to you.

Hope this helps.

Jim Rogers

[bigshow]

you answered multiple future questions i had...awesome!

i didnt know you could offset the spline for instance...

kinda seems like if you can dream it up, have enough wood left over you can BS thru about anything.  I suppose its my engineers job to catch my mistakes, but at the end of the day - its my frame, my design, and i need to know what i can and cant do.

in the books i have - Benson, Sobon, Chappell, TFGuild red book (maybe they're all red!) - i dont see much on 'standard' joint design.  Is there are resource out there that does???

[DKR]

I know of at least one timberframe company that would use an allthread from the outside of the post into the white beam (past the diminished housing) to handle the stress on the joint and the outward thrust on the post generated by the slope of the roof.  (I'm not an engineer, so excuse my layman's explanation).  The allthread is hidden so that you can't tell it's there once you get the floor on the beam.  If you don't have a floor there, guess you would have to plug the hole.

[Jim_Rogers]

As to standard joinery details, I don't know of any published book other
than the historical joinery series of articles by Jack Sobon.
I believe you can download them from the guild site.
At:http://www.tfguild.org/joinery/joinery.html
If you can't let me know, as I believe I have them in pdf and I can forward
that to you.
Some general frame rules or joinery rules are that the tenons are 1/4 of the
thickness of the timber. So, if it is a 8x8 the 2" thick tenons, and if a
6x6 then 1 1/2" tenons. That's about it other than pegs are usually half the
tenon thickness, that is 1" for 2" thick tenons, and 3/4" for 1 1/2" tenons.
Other than that the only thing about beam sizing is to make the large enough
to hold up the load, and have enough bearing surface to also hold up the
load.
This takes understanding the math and doing it for each joint.
Jim Rogers