Measure lengthwise across the frame. Multiply this number by two and add 12 inches. Use scissors to cut a number of lengths of spring twine equal to the number of rows of springs that run lengthwise in your piece. Repeat this process for the row of springs that runs crosswise.
Use an upholstery hammer to drive two upholstery tacks halfway into the frame at the center of each row of springs, both lengthwise and crosswise.
Form a clove-hitch knot at the end of one of the lengths of spring twine cut for the lengthwise springs. Loop the knot around the upholstery tacks at the end of one lengthwise row of springs. Finish driving in these tacks with an upholstery hammer.
Pull the spring twine up from the tacks to the top of the spring. Keep the twine taut.
Press the edge of the spring closest to the frame down to the desired height. This should be a minimum of 3 inches above the top of the frame. If the springs are still tied when you first uncover them, measure from the frame to the top of the springs, and retie the springs to this measurement.
Tie an overhand knot on the edge of the spring with the twine.
Draw the twine directly across the spring to the other edge. Keep the twine taut, and tie an overhand knot.
Pull the twine from the edge of the first spring to the edge of the next spring in the row. Tie the twine to the spring with an overhand knot.
Tie each spring in the row in this manner. Tie the twine to the tacks at the end of the row with a clove hitch knot. Drive the tacks firmly against the frame.
Repeat this process for each row lengthwise and then crosswise.