Post/Plate Joint Question

[tadamson]

I'm building a gazebo from some plans I got online and the post to plate joint is not clear to me.  I've done my best interpretation of the plans in SketchUp below, but it doesn't seem right.  I'm looking for some input on the best way to join two plates to a single post.  The top plates will all be level with each other as a hipped roof will sit on top.

In the pic below, the red plate has two mortises - one for the post and the other for the adjacent plate.  In the second pic, you can see the blueish plate only sits on the post an inch, which doesn't seem like much support.  I was also thinking that the red plate will have too much material removed with both mortises very near each other.

The posts are 8x8 and the plates are 8x10 (nominal).

Thanks, and let me know your thoughts.




 

[Jim_Rogers]

Shorten the post tenon to 4 inches. increase the plate to bare on the post by at least 1 1/2".

Just my ideas.

Jim Rogers

[tadamson]

Much appreciated.  I'll update the model and see how it looks.

Thanks

[tadamson]

Here is the updated joint.  Both tenons are 4" and the plate sits on the post 2".  That required the opposing plate to have a rabbet.

The housing lines kind of confuse me a bit, so hopefully this is correct.

I'm also not quite sure how I'll put these altogether yet!  If the posts are installed with no flex, not sure how I will slide the plate with the tenons into both posts at the same time? 

[Don P]

Some form of half lap would allow one of the plates to drop in. It can also be some form of half dovetail. A tenon can come up from the post.


 

 


 

[tadamson]

Here is the latest version.  Post tenon is 3.5 x 3.5 x 7.  Plate A can sit down first and then plate B can go on top, with the post tenon going in 2.25".

Should I alter the post tenon size to something else?



 

[Jim_Rogers]

Tenon standards are 1/4 the timber thickness. So if it's an 8 thick then 2" if it's a 6 thick then 1 1/2". These standards make it easy to use your framing square to layout the joint and then check the dimensions once cut.



If you make your tenon 3 1/2" square you are removing more wood then necessary and you're making it harder to check the actual sizes of the tenon and mortise. Unless you have a piece of steel that is 3 1/2".
One of the rules at the top of this sections says:
The "Golden Rule": Design joints to do the same structural task assigned to the loaded timber without putting the capacity of the receiving timber at risk.
and:
1). Cut the joints and arrange the fastenings so as to not weaken the pieces of the timber that they connect as little as possible.

Good luck
Jim Rogers

[Don P]

Look back above at the pics I posted. Notice that both plates are bearing on the post. The easiest way might be to pull the lower part of the green plate forward 1" and do the same to the upper part of the red one then switch your model to x-ray view and clean up the interferences. Once you cut one it becomes clearer. I'm not hard and fast on that small stub tenon. You are playing a balancing act with tenon strength and mortise strength. There is basically too much going on in a small area so it is not an ideal joint.

[tadamson]

Thank you both for your input, much appreciated.  I suspected that my tenon was too large.  Here is a 2x2x7 post tenon.  I've also adjusted the plates to ensure both sit on the post.  Right now, the bluish plate sits on the post an inch.

Will I need a housing on any of these joints?  I'm having a hard time picturing if I need any reduction.

I'm thinking about adding some kind of mechanical fastener to tie all 3 pieces together as well.

[tadamson]

I just came across this on timberframehq.com.  Perhaps this is a better connection method?  The purple plate sits on the post and is just connected to the red plate with structural screws and a 1" housing.


 

[Don P]

That is a better post tenon but a worse plate connection, pick your poison. That hip is waaay overnotched.

On your last drawing, now pull the notched end of the red beam this way 1"  into the blue plate and you've got it.

[tadamson]

I reduced the lap joint by an inch.  Is this what you meant?



 

 

[Don P]

By jove I think you've got it 

[tadamson]

Great, thanks very much for your help!

[tadamson]

I'm thinking I may need to cut a housing into the plate lap joints so the post sits on the inner 7.5" timber?  Basically where the red line is scribbled...Otherwise it would seem possible that corners of my hipped roof might not be on the same plane?

I just can't decide if a housing is needed or not...