Tape measure with variable preformed stressed spiral spring retraction system
A tool, such as a tape measure, including a spring-based retraction system is shown. The spring-based retraction system is driven by a spiral spring, that has a variable preformed stress profile along the length of the spring.
1. A system for forming a variably stressed tape measure spiral spring comprising:
a sheet material;
a smoothing station;
a heating station; and
a stressing station configured to form different levels of preformed stress in different portions of the sheet material, the stressing station comprising:
a bar configured to engage with and deform the sheet material as the sheet material moves around the bar, wherein the bar is movable relative to the sheet material such that a bend radius induced in the sheet material is varied by altering a position of the bar relative to the sheet material;
wherein the sheet material when wound forms a tape measure spiral spring.
2. The system of claim 1 , wherein, when the bar is in a first position and the bar engages a first segment of the sheet material, a first bend radius is induced in the sheet material.
3. The system of claim 2 , wherein, when the bar is moved toward the sheet material to a second position and the bar engages a second segment of the sheet material, a second bend radius is induced in the sheet material.
4. The system of claim 3 , wherein the second bend radius is different than the first bend radius.
5. The system of claim 3 , wherein the second bend radius is less than the first bend radius.
6. The system of claim 3 , wherein the first segment of the sheet material has a first level of stress, and the second segment of the sheet material has second level of stress and wherein the second level of stress is greater than the first level of stress.
7. The system of claim 1 , further comprising a storage device, wherein the storage device includes an arbor configured to store the spiral spring.