Consideration with Post Top Tenons

[Preserved]

I've got a basic plan and my wood ordered.  At this point I'm looking closer at "what joints where".

Are there any special considerations to be taken for post top tenons? I'm building a variant of Sobon's shed, with a continuous top plate over my bent posts.

Sobon mentions briefly that a center bent post top is different than a corner post, but gives little explanation.  If I'm understanding Square Rule, then the end bents would have post top tenons that mirror each other but what about the middle bent posts? Could I just pick either outside reference edge?

Possible silly question: Post top tenons aren't housed into the top plate mortise from the pics I've seen, but to get the top plate level, they would need to be..correct?

My apologies if I'm mixing up my terminology here. I'm trying to absorb lots of information and some of it is still swimming around in my head. 

[Bridgewright]

I'm guessing Jack is alluding to to relish beyond the tenon. This is important because the brace puts the plate into tension under windload.

Maxing relish at the plates ends is achieved by "Boxing the tenon" essentially necking it down so it is several inches short of the reference face of the post.

In outbuildings this is augmented by projecting the plate beyond the post face. This is a good place to sit a "Flying" rafter so you also have an overhang on your gables. If you only ordered plate stock the length of your building, split the "trim" the mill provides to either end.

It depends on what layout system you are using, but yes in square rule you house to bring your stock to a common dimension and to cancel wind.

[addicted]

That's exactly what he said during his class last month.
Rusty

[Preserved]

Maxing relish at the plates ends is achieved by "Boxing the tenon" essentially necking it down so it is several inches short of the reference face of the post.

Not sure I understand this. "Boxing the tenon"? 

My plates will overhang past the posts a bit for a little overhang at the gable ends. 

Thanks

[Preserved]

Thinking more on this....

Should I shift the post top tenon further away from the reference face of the post to keep a good amount of relish on the outside edge of the top plate? 

Is this necessary if the top plate overhangs past the post a few inches?  I'd like to keep my joints simple. 

I've seen many good illustrations of post/girt joinery, yet few post top illustrations. Can't get my head around this.

[Jim_Rogers]

I have photos to show what boxing the tenon is, but I don't have time right now to post them.
I'm in Canada at the TFG eastern conference.

If I can get some time tonight, I'll upload them if I can, internet up here can be somewhat slow at times.

Jim Rogers

[Jim_Rogers]

Ok, so I got a few minutes to show you what I think he means by "boxing a tenon".

However this tenon is not a top tenon, but a stub tenon on the bottom of a post.
This post is a doorway post and the sill ends right at the doorway opening.



In the above image you can see the mortise and if this mortise went all the way to the end of the sill then there would be nothing there to hold it in place, as it could just slip out of the mortise if someone pushed it toward the center of the doorway.

To prevent this from happening the mortise is cut back 2" away from the end of the sill, and then tenon is made to fit this mortise. So therefore the tenon would be "boxed"...

[Jim_Rogers]

Sobon mentions briefly that a center bent post top is different than a corner post, but gives little explanation.  If I'm understanding Square Rule, then the end bents would have post top tenons that mirror each other but what about the middle bent posts? Could I just pick either outside reference edge?

On any interior bent there needs to be a reference face designated. So what that means is someone, like you as it is your frame, decides on which side of the center bent is the reference side. It is usually the side that is up when you assemble it. So that you don't assemble it upside down.

Looking at your picture of your frame you have designated the side away from the existing shed. I know this as the braces are set to that side.
So that side of your bent is the reference face. Now the outside of the building is also a reference plane, but it is not the primary reference plane and it is adjacent to the reference face so we call it the adjacent face. This face and the reference face meet at a corner of the post. This corner is the corner where all the dimensions are pulled from. Meaning this corner is the zero end of your tape.

So if your "general frame rule" is that each tenon is: { 2" off the reference face and then 2" thick} it would be measured from this corner. Now this tenon is going vertically into the plate, so it has to go with the plate from end to end as it has to follow the rule that says that all mortises go with the grain not across it.

If you're not sure what I mean by this look at post #2 in this thread: https://forestryforum.com/board/index.php/topic,6403.0.html

Next, we now know that the tenon is going to be 2" off the reference face and then 2" thick, and it as to follow the plate,  in length, that means we're going to lay it out 2" off the adjacent face and then make it 2" thick.

After we have to establish it's length. In the center bent the tenon can be a "full" tenon as it doesn't need to be "boxed" as there is plenty of wood on either side of it. Then tenon then has to follow the next rule of your "general frame rules" which should be 1/2" less then the timber size. It the post is a 8x8 then this tenon is 7 1/2" wide going from the reference face back towards the other side of the timber know as the opposite reference.

I have created the tenon on the top of the post and it's mortise to the plate and I have rotated the plate so you can see the mortise and housing:



This is the way the tenon and mortise should look.

Hope this helps.

Jim Rogers

[Jim_Rogers]

Post top tenons aren't housed into the top plate mortise from the pics I've seen, but to get the top plate level, they would need to be..correct?

Post top tenons "are" housed into the top plate in order for the top plate's mortise joint to follow the general frame rule that all timbers are reduced down to the next 1/2" in size.

[Jim_Rogers]

My plates will overhang past the posts a bit for a little overhang at the gable ends. 

If your plates are going to hang over the end bent's top tenon then they can be "full" tenons the same shape and size as the middle bent's post's top tenon as shown above.

[Jim_Rogers]

As you're new here maybe you didn't know, but off site pictures are not allowed to be posted on this forum.

In order to post a picture here in your questions or comments you have to create an album and put your pictures in there.

There are instructions here on this forum about how to do all that, and you need to do that so that you can show your frame and we can help you with it's design and joinery.

Jim Rogers

[Preserved]

Thanks for taking the time Jim.  I just figured out how to include photos so here is my first shot at Sketchup:


You mentioned my braces all flush with the outside bent, away from the existing shed indicating a reference plane. That was'nt intentional. I created the one bent then tripped it for the other two. 

By the way, I live in an an area ripe with old homes, barns and antique shops. I spent the day today poking through some shops & barns. I did buy a nice old crosscut saw, no chisels worth mentioning. Found one place that had tons of tools, guy tells me he got in two boring machines this past summer and sold them both for $75 each. Good working order too.  Always lots of saws, planes, drawknives and such.

[Jim_Rogers]

We'll need to get together and go over things like reference faces and tools.....