Stretcher to Post Joinery

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Chris Hall
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Stretcher to Post Joinery

Sat Jan 23, 2016 2:24 pm

A request was made to talk about the joinery options and detailing for connections between post and stretcher. As I started drawing, I reflected that this is a slightly involved topic, and not something I think can be explained all that well in brief. That said, I don't feel like spending the rest of the day on this either, so instead, I'll chip away at it and people can throw in comments or heckles as they see fit.

I think the following drawing outlines the main conditions where we have to devise joinery between stretcher and post. The post section is 'a', the stretcher section is rectangular, measuring 0.33a x a:
Nuki meets post 2.jpg
Nuki meets post 2.jpg (216.82 KiB) Viewed 8446 times
I have centered the stretcher on the post face in each case.

At the bottom, we have the stretcher terminate at the post, though it can also pass completely through the posts and continue to some extent. The main thing is that it does not connect to further structural members beyond the post. It could also connect to the top or bottom post end.

In the middle we have a stretcher which meets the post and passes though, connecting to other structural members beyond in each direction. The stretcher itself can be one-piece as it passes through the post, or it can be two-piece, each of which joins to the other inside of the post. One could also have the end of the stretcher splice continue beyond the bounds of the post if desired.

On the top of the drawing we have a stretcher meeting the top of a post. Once again, the stretcher can be one-piece or two-piece. The post may connect to another member above the stretcher. This is the weaker form of connection mechanically as it bears on a minimum of 3 surfaces in the joint, one of which is end grain, while the stretcher passing through the post somewhere must meet at least 4 faces in the joint, two of which are end grain surfaces. Essentially this is a bridle joint, an open mortise and tenon. Not the strongest, and reliant upon glue for integrity, but there are some better ways to deal with this connection.

All these joints are strongest if the stretcher is one piece instead of two piece.

Stretchers may also meet one another at a post at a right angle, and again, the respective stretchers might terminate at the post, might pass through the post to some further point of connection, and may be one-piece or two-piece:
Nuki meets post 3.jpg
Nuki meets post 3.jpg (274.12 KiB) Viewed 8446 times
Now, it should be acknowledged that the above examples are dealing only with orthogonal relationships between the parts. The members could also meet at varying angles in relation to one another. Some joinery options will work for such cases, others won't.

So, there is a considerable range of possibilities to look at. And the above is only considering situations where the stretcher is 1/3 as wide as the post. All the same connections can be considered for stretchers that are 2/3 as wide as the post, 1:1, or even where the horizontal members are larger sections than the post. So, I'm going to stick to the 1/3 case for now.
Jack_Ervin.
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Re: Stretcher to Post Joinery

Sat Jan 23, 2016 4:42 pm

Chris,
You have one in this audience to see how you execute this. I am in the process building a pair of the type horses that started this discussion. They will support my 4'X12" beam. Was intending to do pinned mortise/tenon but will see where this goes and will incorporate what you show here. My sticks are western red cedar because that is what is locally available and they will be utility. My stretchers are 1:3 to the post. I'll post up if that will encourage you and others.
Jack
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Chris Hall
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Re: Stretcher to Post Joinery

Sun Jan 24, 2016 5:47 pm

Thanks Jack for being willing to contribute.

The first case to deal with is a single stretcher meeting the post and terminating at that location:
Nuki to post connections 1.jpg
Nuki to post connections 1.jpg (97.78 KiB) Viewed 8416 times
The simplest connection would be to butt the stretcher against the post and toe nail in a nail or two:
Nuki to post connections 2.jpg
Nuki to post connections 2.jpg (359.47 KiB) Viewed 8416 times
Other than the case where the stretcher is driven directly against the post face, the only resistance to loading on the stretcher would be provided by the nails. Nails are ductile and strong fasteners, but form points of condensation and will induce rotting in their location, so the lifespan is not that great. Look at any nailed wooden fence and you will see the first spots to rot are the locations of nails and locations where wood meets the soil. A nailed connection gives marginal strength and a marginal lifespan. Primary virtues are that it is quick and easy to form, and therefore inexpensive.

The nailed connection can be significantly improved by mortising a shallow housing on the post, which improves mechanical strength considerably:
Nuki to post connections 3.jpg
Nuki to post connections 3.jpg (249.83 KiB) Viewed 8416 times
Once we start looking to joinery as a means of attachment, arguments for cheap and fast methods gradually begins to recede in importance.

In this situation, a mortise in the post will initially provide the greatest benefit of mechanical strength for loads on the stretcher in a vertical direction:
Nuki to post connections 4.jpg
Nuki to post connections 4.jpg (193.35 KiB) Viewed 8416 times
If the stretcher were to be loaded in a cross-wise direction, then the stretcher section is inappropriately oriented.

A shallow mortise provides a measure of mechanical strength, so deepening the mortise will be an improvement, and a peg can be added to fix the connection:
Nuki to post connections 5.jpg
Nuki to post connections 5.jpg (179.06 KiB) Viewed 8416 times
Nuki to post connections 6.jpg
Nuki to post connections 6.jpg (168.38 KiB) Viewed 8416 times
The mortise has been stopped shy of going through; a connection with the tenon going right through is essentially similar. The peg adds a modest amount of strength and stiffness to the joint, but primarily this connection would be strong against the stretcher being loaded vertically, like the rung of a ladder:
Screen-Gems-Wooden-Ladder-SGT086.jpg
Screen-Gems-Wooden-Ladder-SGT086.jpg (125.67 KiB) Viewed 8415 times
Strictly, speaking, the above is a mortise and tenoned ladder, with tenons shouldered, however the essential point carries through. The main load to be resisted is vertical, and loads which pull or push along the line of the stretcher are minimal in nature. A peg is not a stiff connection, and in a small ladder that is no issue, particularly given the number of elements connected to one another, and provided that the mortises are close-fitting to the stretchers.

In the ladder the stretchers are carried right through the verticals, which are slender in section, thus it makes sense to carry the stretchers right though to provide adequate relais beyond the pegs.

Instead of pegging, we could have used an adhesive. This will work in the short term, however the direction of greatest wood movement in the stretchers is 90˚ to the direction of greatest wood movement in the post, so over time the wood movement will weaken the connection significantly. So, if an adhesive is specified, ideally it would be one which had some inherent elasticity to accommodate wood movement. Rice paste glue would be one example.

The next post will look at some other options for the same connection of single stretcher to post.
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Chris Hall
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Re: Stretcher to Post Joinery

Sun Jan 24, 2016 6:20 pm

Before I go any further, I thought I'd check in. Is the above material what folks are interested in or would they prefer I get immediately to some particular configuration of interest? I think maybe I shouldn't presume to make something like this into an exposition. Willing of course to do just that, but, well, don't want to lecture broadly on a topic which might be of outside of or beyond the scope of what people were wanting.

I always think that if I start in with a particular example, it is only natural that people might have some "why do it this way and not that way?" type of questions, which can get complicated to answer properly and that leads me to conclude that it is better to just start from the beginning when digging into a topic like this.
Ken
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Re: Stretcher to Post Joinery

Sun Jan 24, 2016 6:37 pm

This is an amazing post!

:lol: Sorry, couldn't resist.

I'm very interested in this kind of material. For me, from the beginning is definitely the best point to start. The more of this the better, thank you for doing this.
Gadge
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Re: Stretcher to Post Joinery

Sun Jan 24, 2016 7:59 pm

For me, from the beginning is definitely the way to go, as long as it is leading to a refinement of the saw horse design. I appreciate your willingness to develop the explanation from the start.

Gadge
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Re: Stretcher to Post Joinery

Sun Jan 24, 2016 10:06 pm

What they said. Thanks for sharing Chris, it's all greatly appreciated.
Jack_Ervin.
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Re: Stretcher to Post Joinery

Sun Jan 24, 2016 11:09 pm

Chris Hall wrote:The first case to deal with is a single stretcher meeting the post and terminating at that location:
Chris,
I'm definitely with the others as to what you have to develop for different methods of connection of a stretcher to a post. I believe we all have procedures to learn or have confirmed. At present I have my mortises chopped to width but not finished to length. I have not cut tenons yet and will hold off until all methods of connections are explained. As to the above connection using pins, I'm assuming they are drawn to the shoulder and down.
I think Gadge and my end results for saw horses are the same.
Jack
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Brian
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Re: Stretcher to Post Joinery

Sun Jan 24, 2016 11:20 pm

Thanks for this post Chris, I am excited to see a topic like this fleshed out in such a manner.
dmccurtis
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Re: Stretcher to Post Joinery

Mon Jan 25, 2016 12:44 am

This is very interesting. Looking forward to seeing where it goes.

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