The Story Behind This Sofa
A tub back is one continuous curved member, and that is the whole difficulty. On a conventional sofa the back rail is straight and the arms are separate assemblies joined to it - three simple parts. Here it is a single sweep that has to curve in plan and hold its shape across the full width, with no joint to absorb movement and nowhere to hide a correction.
The rail is either laminated in layers around a form or cut from much wider stock with the curve taken out of the solid, both of which waste a great deal of timber. Grain has to follow the curve throughout - short grain at any point in that sweep is where a tub back cracks.
The upholstery is equally unforgiving. Every panel is cut on a shaped pattern and eased onto a compound curve, and the quilting grid must stay parallel to the rail all the way round the bend. A grid that drifts as the curve turns is instantly visible.
It is more work than a straight sofa for the same number of seats. What you get back is a smaller footprint.