Futon Frame Finalized

For the past few weeks I've been narrowing in on my design for the futon frame using Google Sketchup. I know I'm starting to sound like a fanboy for this program, but it's hard not to be impressed with how simple it makes 3D modeling. That's good because I'm no engineer :)

I've wanted to go the direction of sliding the seat section to cause the seat back section to rise, but I needed to figure out the right linkage, and it came down to creating 5 'scenes' in the model, where the seat back would pivot 14 degrees between each scene (for a total of 70 degrees, the ideal angle for a seat back measured from the rear). If the seat section were not to slide backward, then the pivot point on the seat back would have to be a groove with a slight arc to it. But, in having the seat slide, the model shows that the seat back pivot point can indeed be a fixed point. So a carriage bolt could serve to connect the seat back section to the riser arms. Drilling holes is much easier than machining grooves!

Here are the 'up' and 'down' pictures showing the top/front of the frame:

Notice I've updated the model to show the 1 X 6's previously added. As the seat back section is lowered, the seat section slides to the edge of the support rails.

Below are shots from the underside, showing off the linkage:

I've added the 1 X 4 runner stiffeners to both sections, the seat back cross-braces that the riser arms connect to, bolt positions, and the rear connection points for the riser arms. My thought is a 1 inch steel pipe, maybe EMT, that passes through the riser arms on both sides. Construction adhesives and a couple screws should hold each in place. The outboard sections of the pipe would be held to the underside of the support rails with some pipe brackets, and allowed to pivot freely inside the brackets. I'm thinking of first mounting the pipe brackets to a pair of L-brackets, making it easier to attach them to the rails - from the sides instead of from underneath. 

As you can see, having the pivot point underneath provides some tilt to the riser arms. What I don't know is how much force will be needed to push the seat section to get the seat back to rise, but it will definitely need the pivot point to be below the plane of movement to 'kick up' the seat back.

If all goes well this weekend, the next post should have more than just illustrations to show!