Step one - seat construction

Using three 8x1 1/2in screws, affix the seat supports to the underside of the seat. If using a countersink, make sure this is done before screwing on the supports

To get the Ironbridge's 'egg' shape, cut the edges of the seat and seat supports as shown in the diagram

Using a tape measure, find the center point of the seat. Mark this, and a point 9in (approx 25cm) either side of the centre point along the centre line of the seat. Drill pilot holes at these points, then affix the seat posts to the underside of the seat using one 8x2 1/2in screw per post. If using a countersink, make sure this is done prior to screwing on the seat posts