This section is from the book "Spons' Mechanics' Own Book: A Manual For Handicraftsmen And Amateurs", by Edward Spon. Also available from Amazon: Spons' Mechanics' Own Book.
If a spring edge is to be made, the middle springs should be soft and 8 or 9 in., and be lashed in place farther from the rails, with canvas laid over and tacked to the top of the rails on the extreme inside edge. Soft 6-in. springs are used at the edge, fastened securely in a vertical position on the rails, all to one height, the cord holding them being best knotted to the top ring of each spring, and fixed down on each side by 5/8-in. tacks. The shape of the edge is formed by bending spring wire to the exact shape of the rail, and securing it with string tightly to the top ring of the spring edge; the canvas covering is sewn to the spring edge and to the canvas already on about 3 in. from the top level, aiming to allow the two sets of springs to work independently of each other. The first stuffing should be soft and free, with a bold overhanging stitched edge, finished on the wire edge; a strip of canvas sewn to the wire edge which is tacked to the seat rail permits the height of border to be regulated by pulling to shape; the second stuffing may be finished with a bold cord just under the roll, with a frill or one row of buttons on the border.