Cutlery – Sheathed – Sliding blade
Patent
1990-01-08
1991-08-27
Yost, Frank T.
Cutlery
Sheathed
Sliding blade
30125, B26B 500, B25F 300
Patent
active
050421549
DESCRIPTION:
BRIEF SUMMARY
This invention relates to utility knives.
Utility knives are cutting tools capable of a wide range of uses basically comprising a handle into which a replaceable knife blade is fitted and immobilised so as to protrude from one end.
In some instances the knife is such that the blades must be completely removed and disposed of when the exposed end becomes blunt, at which time a new blade is fitted. More commonly, the knife has a blade shaped to possess two sharpened ends (e.g. shaped as a symmetrical trapezium with the long edge sharpened) so that when one end becomes blunt the blade can be taken out, reversed, and replaced to expose the other for use. Only when this other end becomes blunt is the blade completely replaced by a new blade. In a preferred form, such blades can also be "retractable" i.e. selectively extendable to any one of a number of immobilisable positions.
In recent years the blade has been embodied as a long metal strip, sharpened along one edge and provided with score lines or like lines of weakness across its width at an acute angle, that is, so as to come to a sharp point at the sharpened edge. As for a simple retractable blade this elongated blade is supported within the handle on a carrier, and a resilient part of the carrier is biassed against the teeth of a longitudinal rack. A press button extending through a longitudinal slot in the handle enables the user to press the resilient part of the carrier out of engagement with its rack and slide it up or down within the handle. Thus, the blade can be retracted for safety, or can be forwarded to a desired operative position. When desired, since a line of weakness is apparent, beyond the handle, the blade can be broken transversely to expose a new sharp point and sharpened edge portion.
Such utility knives often have handles formed essentially as two longitudinally divided part shells, the exact parting line along the handle being designed in practice for reasons of function or appearance not to be a simple straight longitudinal bisection.
Originally, the part shells were held together by one or more transverse threaded bolts. To change, or reverse, a blade the bolts were unscrewed, one shell was removed, and the blade manipulated as necessary. Typically a "replaceable" blade, whether retractable, and whether for single use or double use is provided with holes or notches to fit by mechanical interegagement within the handle so as to resist longitudinal pressure (otherwise serving to push the blade back when in use) and for replacement the blade has therefore to be removed from and fitted into such engagement with corresponding projections or shoulders. Transverse clamping effect on the blade, also serving to grip the blade against movement, does exist but is usually of secondary importance against such longitudinal movement. It may however be a significant protection against lateral movement of the blade.
More recently, the so-called "wedge-lock" assembly has been used. In this, the part shells, at a forward location of their parting line (and on both side regions) are formed with a wedging interlock so directed that minor longitudinal movement of one part shell relative to the other causes the wedge formations on the parting line to slide one on the other and thereby draw together, or release, the part shells in a transverse direction. This minor longitudinal movement and thus the clamping or releasing of the part shells can be achieved by a single bolt with a knurled head for finger operation, located at the rear of the handle and threaded in one shell while bearing on the other.
Such a "wedge lock" assembly is particularly useful for the knives with retractable blades. This is because, from time to time, the blade must be retracted or must be advanced and then fixed again. The clamping together of the two part shells, even if it does not have a major effect in resisting longitudinal pressures in use, does militate against easy advancement/retraction of the slide over its rack, and it is usually preferred to slacken the shells slightly
REFERENCES:
patent: 3660895 (1972-05-01), West
patent: 3906625 (1975-09-01), Gringer
patent: 4005525 (1977-02-01), Gringer
patent: 4240202 (1980-12-01), Gilbert
patent: 4615118 (1980-10-01), Ihata
Heyrans, Sr. Paul M.
The Stanley Works Limited
Yost Frank T.
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