The legs were to be attached to the base the the seat, from above – through the use of t-nuts that are counter sunk flush with the plywood base board. The t nuts have a threaded insert that would sink into the base board, allowing threaded bar (inserted into the legs) to screw in from below. This method is quite often used in industry for attaching sofa legs – however these are generally not splayed, tapered or as great a distance from the ground, therefore i wanted quite a chunky threaded bar – no less than M8 for support, , that would be araldited into the leg to the would be no movement from the bar inside the leg, to cause complications with stabilising the chair.
Accurately placing the legs proved quite a challenge, as the shape was very irregular and there was no straight flat surface to use as a measuring point. The measurements were taken from the furthest point on each side, measuring in toward the centre of the seat.
The seat frame was propped up on a box, allowing me to wedge the legs under the frame for placement. This was a lengthy yet necessary process, which highlighted some problems with the chair form – resolved due to this process – which would have caused quite big problems if found later in the making process. The cross bars were not level with the ply base board, and not wide enough to fully support the width of the leg. This was a problem as it was the angled join between the top of the leg and the seat base is where the majority of the pressure would congregate, if this wasn’t flush the leg could snap.
The leg placement was decided and marked out on top of the base board. Wider pieces of pine were screwed into the underside of the base board, filling in the space between cross bars, so the top of the leg would be supported.
The t nuts were 30mm diameter and 11 mm deep, with an M10 thread insert. I used digital calibers to measure the diameter of the tube , to get a corresponding drill bit (12mm) which provided a push tight insert. the top of the t nut was countersunk slightly by drilling a 32 mm dropped section , before using the twist drill bit to drill through the base board completely. The t nut was then secured using three screws through the face plate into the ply board.
Whilst the frame was on the box, i tested out some sample widths of walnut for the skirt, finally deciding on 6 cm, so as not to try and compete with the width of the box top section above it .