The next step is to prepare a gluing cradle for the back braces.  The back will sit on the supports and the cradle is used in the ‘go-bar’ deck to glue the back braces and apply the correct curve to complete assembly..

Left -A close-up of the strengthener in the go-bar deck. Right - back braces being glued. The back is resting on a sheet of ply which is evenly distributing the curves imparted from the cradle below it.

Making An Acoustic Guitar - Page 10

The go-bar deck. Every home should have one. Strips of ash under tension from bending apply downward pressure on the piece being glued. It may look like a Heath Robinson contraption but it works really well and most small guitar builders still use them.

Here the central strengthener is being glued to the back before gluing the back braces.  The strengthener strip is cut from an off-cut of the top blank. The grain runs horizontally - perpendicular to the grain in the back.