The photos below are of a dining chair which I was asked to glue up. One other problem with this chair was that the seat had a crack running with the grain from back to front. On a plank bottom chair, this would mean gluing the two sections together, but on this particular chair, the seat had boards underneath preventing the seat from coming together. The answer was to insert a long wedge in the gap, carve it down so that it was flush, and touch the wedge up to look like the rest of the seat.
The wedge was cut at a 5 degree angle on the table saw and several kerfs were cut into the wedge across the grain so that it would bend to conform with the seat.
The chair with the spline inserted in the seat. the joinery was also getting glued up on the chair.A close up of the wedge. you can see the places where the wedge was cut to conform to the shape of the seat.The wedge after most of the excess material has been removed.The seat after it has been sanded and touched up.