Morris Chair Inspired Couch

[Chestnut]

So I'm getting this journal started a bit early. it's going to be a long time until this gets done. This is just a fair warning for those that are excited that i might finish it in a couple months. Also i like to think about things and process them over a long period of time.

I drew up a 3D model in CAD mostly to try and help me visualize a solution to the backrest. There are a few major concerns with this design made couch. The first is how to attach the backrest with out completely redesigning the arm and leg assemblies. The 2nd is' keep the back rest removable. I NEED to be able to get this out of my basement shop with out having to tear down a wall . I came up with 2 options both very similar. I plan on making the back stiles extend further down and hook into a leg that is attached to the front rail with a connecting piece. To make sure that comfort is maintained the top of that board is going to follow the frame for the seat.

The above images show the 3D model. My question to the masses is this. I had planed on either bolting the stile to the middle 2 legs and i know this will work. I was going to use wooden heads similar to those on the pegs that hold the stiles on the Morris chair to cover up the bolt head. The other option is to do a sliding dovetail. The main question is then. In your opinion will the sliding dovetail work and will it be better than the bolted connection?

[Chet]

I think the dovetail will work and would be the more elegant choice.  I think my decision process would be something like this - is anyone going to see this part of the couch on a regular basis, is the back of the couch going to be in the open away from the wall, like in a large room?  Then I would give the dovetails a harder look.  But if this is going to be against the wall then I would just go with bolts as the solution

[Chestnut]

3 minutes ago, Chet said:

I think the dovetail will work and would be the more elegant choice.  I think my decision process would be something like this - is anyone going to see this part of the couch on a regular basis, is the back of the couch going to be in the open away from the wall, like in a large room?  Then I would give the dovetails a harder look.  But if this is going to be against the wall then I would just go with bolts as the solution

My thought with the bolts is the wood cap would tie to the pegs that hold the side stile to the leg and arm into the middle two stiles. There is no reason that i can't just do the sliding DT and just put in false pegs.

[Chestnut]

I bought a dovetail bit today to do a trail run on the sliding dovetail. I'm really curious about how strong it is. Best way to figure out is to do a trial piece and see if it will support my weight.

While i was doing some mindless stuff at work i brainstormed another idea. To run the stile into the leg similar to a bridle joint and then use pins to hold it in place. This is tarting to make me realize how complicated this is going to end up being. Lucky it can all be figured out by working in steps and using relative dimensions.

[RichardA]

I think that the question that Chet asked has a ton to do with the final construction.  Is it going to be open for view in every direction, or will it be limited to the front and the two sides?  Either way, the construction has to be finalized outside of the shop, since you can't get it out if completed within the shop. Do the base and the arms as one complete section, [it'll get through the door] and the back as another section, [it to will get through the door]. Mate those two sections in it's place.  Since I haven't built the Morris Chair project, you'll have to rely on your experience building those to adapt a way to get this unit where you want it.  Will, when completed, you be able to get it out of the house if you move? Can you break it down again if you have to?

[Isaac]

That connection will mostly be in compression. When someone sits down and leans back, the force at the top of the stile will cause a rotation about the top of leg, and the remainder of the stile, below the top of the leg will largely be in compression. However, at the very top, you'll have a tension force, which could split the leg. You also have to think about how the bottom stretchers interact with the leg. If those are mortised into the leg, the meat left behind for the proposed sliding dovetail might not be much. 

I actually think you could channel  your inner Matthias Wandel and build a quick mock up and and give it a load test by locking it in a vice and cranking on it. No need to do the curve of the stile, just make a straight piece the length of the leg and a copy of the leg. Make sure the sliding dovetail is no longer than you are planning to actually make on the real piece. During normal loading, the failure will occur in the leg, not the stile, if it occurs at all. 

[Chestnut]

1 hour ago, RichardA said:

I think that the question that Chet asked has a ton to do with the final construction.  Is it going to be open for view in every direction, or will it be limited to the front and the two sides?  Either way, the construction has to be finalized outside of the shop, since you can't get it out if completed within the shop. Do the base and the arms as one complete section, [it'll get through the door] and the back as another section, [it to will get through the door]. Mate those two sections in it's place.  Since I haven't built the Morris Chair project, you'll have to rely on your experience building those to adapt a way to get this unit where you want it.  Will, when completed, you be able to get it out of the house if you move? Can you break it down again if you have to?

The plan is to never glue the back assembly to the base assembly so that it can be take apart and moved in the future if needed. The chairs which are smaller are quite hefty adding more back slats and cushions would make the couch not only too large in size but probably to heavy to rotate all the different ways necessary to move it.

1 hour ago, Isaac said:

That connection will mostly be in compression. When someone sits down and leans back, the force at the top of the stile will cause a rotation about the top of leg, and the remainder of the stile, below the top of the leg will largely be in compression. However, at the very top, you'll have a tension force, which could split the leg. You also have to think about how the bottom stretchers interact with the leg. If those are mortised into the leg, the meat left behind for the proposed sliding dovetail might not be much. 

I actually think you could channel  your inner Matthias Wandel and build a quick mock up and and give it a load test by locking it in a vice and cranking on it. No need to do the curve of the stile, just make a straight piece the length of the leg and a copy of the leg. Make sure the sliding dovetail is no longer than you are planning to actually make on the real piece. During normal loading, the failure will occur in the leg, not the stile, if it occurs at all. 

Now that you say that looking at the design there isn't going to be a lot of bending force at all in this area. The 2 pins on the arms on the outside will creating a rotate point halfway up the back causing almost all of that connection to be in compression. The only forces that are going to be exerted in that area are from flexing of the back assembly. This makes me a lot more comfortable with the connection. I'll defiantly do the sliding dovetail now if for the only reason as to give it a shot.

[Isaac]

Alternatively, you could probably build those stiles and feet by laminating three pieces of wood together. Just another option.

[wdwerker]

Considering the effort and expense of the cushions etc I would make the rear view pleasant just in case it's visible in a future location. Any engineers around with input ?