Linings are the strips of wood re-inforcing joins between sides and top and sides and back. Linings are usually kerfed (partially cut through at regular frequent intervals) to make them easy to bend.
I don’t love kerfed linings. All those cuts can hold glue that can’t be cleaned out, and also allow glue from fixing the bindings to run into the guitar. So I use solid unkerfed linings, which must be bent beforehand to the same curve as the sides.
Here are the top linings held in place with strong spring clamps while the glue dries. The body is held in the mould which in turn is held by my gun-makers vise.
This vise holds firmly in all positions, can be revolved in two planes and moved closer to or further from the bench. The most versatile vise I’ve come across, I obtained it from Dan Erlewine many years ago.
Below: cittern linings glued and clamped.
Right: the top linings are glued and sanded, and the side re-inforcements (really to stop damage spreading around the sides) are being glued in place. The top linings will be sanded smooth to receive the soundboard.