Thread: Help approaching this couch design..

I assume from the mention of oak faced ply that the intention is to keep the timber surfaces exposed rather than upholster the unit and conceal the frame surfaces. Based on that alone, I make the following comments.

There are a lot of fairly abrupt corners and edges in the design, which would make extended use somewhat uncomfortable for someone getting on in years. Sitting against fairly broad radiuses (vertical to top of ends) would definitely make it more comfortable for me. Also the abrupt corners and edges are a hazard if you have youngsters running around, or older folk that might be prone to slipping or falling, the larger the radius the less chance of serious injury. Car design changed a lot over 40 years for the same reason, to eliminate sharp unpadded corners and edges as much as possible to minimise injuries to occupants and pedestrians in the event of an incident.

Seat depth may be way to deep for comfortable sitting. We bought King lounges 12 years ago and they have a deep seat base in them, but not as deep as you suggest. They are fairly deeply padded, but you can't sit comfortably in them without cushions to support your back, they are too deep. Ideally you want the seat depth to approximate the distance from your back to the back of your knee less a couple of inches to allow for leg movement. In a similar vein, the seat height should allow your feet to be squarely on the floor to facilitate standing up from a seated position. To low and the angles of your body when seated work against you when trying to stand.

Seat back is probably too narrow and low to offer much support to an adult or offer much assistance when standing. It probably needs some rake as well to offer broad support to the back, currently a user would either have to sit with a very square bend at the hips or sit forward and have a sharp back edge supporting a narrow strip across their back, probably just below the shoulder blades.

From a construction perspective, I would do both the seat base and back as torsion boxes, two skins of sheet about 9mm thick separated by an exterior frame of timber, with an interior lattice of ply or timber maintaining the separation of the skins. I would also incorporate some framing inside the ends that these could be fastened to. This complicates the design and fabrication of the ends, but provides a much more sturdy structure overall.

These are just my thoughts, as an older and heavier guy, and you may consider them irrelevant to your situation, that's ok with me, but please consider those likely to visit and use the lounge as well as your current immediate household.

For the arms...
Kerfing board can leave visible ridges on the outside after wrapping in my experience; they can be sanded out, but that's not an option with veneer already on it. What I would be doing is laying up 3-4 layers of 3mm bendy ply on a 19mm ply and hardwood frame, then glue veneer on the whole thing. You should probably have a 70 x 35 mm hardwood rail where the threaded inserts will go.

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For the seat...
Connect it to the arms with giant pin-and-cam fittings and threaded inserts with 1/2" dowels for strength (it doesn't need) to be glued together. I have built dozens of beds with this exact system. If you're worried about sagging, you could add a leg in the very middle; you'd never see it unless you're on the floor.
Connector housing, Hafele Maxifix, for wood thickness from 24 mm - in the Hafele Australia Shop
Connecting Bolt, for Maxifix Housings, M6 Thread, Zinc Plated Steel - in the Hafele Australia Shop
https://www.hafele.com.au/en/product/screw-in-sleeves-with-flanged-rim/000000280003f74200010023/

Pass on the back for now pending design issues noted by malb

Further to what’s already been noted the basic geometry needs looking at.
The seat needs a few degrees of rake as does the back.
If you sit on a flat level seat with a back at 90degrees to it you won’t be comfortable especially if you’re low to the floor.
Look up ergonomics or as that pommy wanka George called it anthropometrics, it’ll give you the good oil on what’s comfy and wot ain’t.
H.

PS. I quite like your design ideas so keep at it.

Following on from a Clear Out’s Post, this is a site I have used.

Ergonomics of sitting

Wow thank you for the responses. My lil brains still processing them, I'll have to take a minute to absorb and get back to you individually.
Also, my apologies for the confusion, I should have included this image too.. Dimensions have been taken from a higher end Ikea couch, with some added depth in the seat. This is still a work in progress.
Yes quite a few friends have mentioned the straight back. I've been in couches with straight backs before — comfy ones, so I've figured I'd find foam with the appropriate density for the back.
If anyones wondering, I'm currently thinking of fixing those floating foam arms in place with straps through the upholstery into the side of the arms somehow. Another idea was to use magnets, but I don't feel that'll be best in a space where phones will most likely be rested. More research needed and open to any suggestions. Thanks everyone!

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Originally Posted by anthonyris

...
Dimensions have been taken from a higher end Ikea couch, with some added depth in the seat. This is still a work in progress. ....

Screen Shot 2020-07-26 at 6.00.22 pm.jpg

"...higher end Ikea..." Does not exist!

Watching the progress of this design. Some of my stuff has had a very, very lengthy evolution.

You also need to think about how the components fit together and stay together; what framing is behind the plywood? And how do the various panels on this design compare to the same components on your favourite, most comfortable couch? The most comfortable chairs rarely have horizontal or vertical surfaces, and, conversely, they rarely have a lot of stuffing.

People are not square!