The Self-Winding Chalk-Line Reel: A Coil Spring That Reels the Line Back

"A represents a small flat rectangular wooden box, with a handle, B, at one end. The box is divided into two compartments by a thin partition, a a. A narrow compartment, No. 1, contains a long flat coil-spring, b b, the outer end of which is fastened to one side of the box, as shown in Fig. 1, and the other or central end of the spring to a spindle, c c, running through the center of the partition a a". "The chalk-line is placed upon the reel so that when it is wound up the coil-spring b is fully expanded, and when it is drawn out for use by the holding-ring f the spring will be contracted or closed around the spindle c c by the turning of the spindle".

**Box.** From plywood make a box 12 × 12 × 5 cm inside with a thin partition dividing it into a 1.5 cm and a 3.5 cm compartment, and glue a dowel handle to one end. Drill a 6 mm hole through the partition's centre and both sides for the spindle. **Spring.** Coil 1.2 m of spring steel strip into a flat spiral, fix its outer end to the narrow compartment's wall with a screw, and its inner end into a slot sawn in a 6 mm dowel spindle. **Reel.** Glue two 8 cm plywood discs to the spindle in the wide compartment, 1 cm apart. Wind 2 m of cotton twine on it with the spring relaxed, thread the end out through a small hole, and tie on a ring. Put marking chalk in the wide compartment. **Test.** Pull the line out 1 m and 2 m, counting the reel's turns through the hole, and let go; time the rewind with the stopwatch. Compare the turns with the notebook, and snap a chalk line with it.

**Jonathan H. Rose** of Mount Sterling, Brown County, Illinois, signed US 59,268 on 14 July 1866; it is dated 30 October 1866. His claim is the coil spring, spindle and reel combined with the partitioned box and handle. **Honest limits.** A plywood box and a hand-coiled strip of spring steel stand in for his wooden box and long flat coil spring, and the line is short to suit that spring. The notebook ignores the line's thickness building up on the reel; its lengths and radii are examples. Your turn counts and times are the result.