Geometrical instruments – Straightedge type – Cord type
Patent
1997-07-28
1999-07-13
Bennett, G. Bradley
Geometrical instruments
Straightedge type
Cord type
2423753, 2423854, B44D 338
Patent
active
059209976
ABSTRACT:
In accordance with the present invention an automatically retractable chalk line device is provided having a housing in which a power spring drives a first large diameter gear through a first shaft. The first large diameter gear is in driving engagement with a first smaller diameter gear located below the power spring. The first smaller diameter gear drives a second large diameter gear located partially above the power spring. The second large diameter gear drives a second smaller diameter gear which a drives a chalk retaining spool, which holds the chalk line. The relative diameters of the two large diameter gears as compared with the diameter of the two small diameter gears provides a large mechanical advantage. A disc brake is mounted for braking engagement with one of the large diameter gears, preferably the second large diameter gear. An arrangement for engaging and disengaging the disc brake with the large diameter gear is provided. This arrangement includes a cam surface and a slotted plate which is resiliently biased into the engaged position by the cam surface. A release button is actuated to move the plate relative to the cam surface to release engagement between the disc brake and the large diameter gear. The housing for the chalk line retraction device includes an opening in which a plate is movable between an open and closed position to allow for introducing chalk into the assembly adjacent to chalk line. The housing is provided with an exit portion where the chalk line exits and an anchor is provided at the end of the chalk line. The strong power spring and the mechanical advantage achieved from the dual large gear and dual small gear assembly provides a large mechanical advantage to enable a longer chalk line of up to a hundred feet or more to be utilized. The disc brake acting on a large diameter gear provides very effective braking of the system. The deactivation device for the brake system is readily accessible and convenient to operate. Chalk is readily inserted into the housing through sliding plate assembly for loading and unloading chalk.
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patent: 5014437 (1991-05-01), Sun
patent: 5042159 (1991-08-01), Millen
Bennett G. Bradley
Cummings Henry W.
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