Spring assist knife
A spring assist folding knife and method of biasing a blade in a folding knife. The folding knife includes a blade, liner, and handle. The blade includes a first recess for receiving a pivot pin. The blade includes a second recess offset from the axis of rotation. A latch cam having an offset pin is located relative to the second recess. The liner includes an arcuate slot in which the offset pin of the latch cam is located. The arcuate slot within the liner or handle also includes a convex extension. A spring is configured to provide a force in the direction of blade opening and provides the force throughout the entire range of blade motion. The spring applies its force to the offset pin to bias the blade in the closed position until the blade reaches a predetermined angle. Then the spring biases the blade to the open position.
1. A method for opening a blade of a folding knife, the method comprising:
applying at a closed knife an external force configured to open the blade by and moving a position of a latch cam within the blade;
and moving a position of an offset cam pin of the latch cam from within a convex extension positioned at one end of an arculate slot to substantially within the arcuate slot formed in a reference piece of the knife;
exerting an opening force configured to open the blade to a fully open position without additional external force; and
wherein the step of moving the offset cam pin comprises rotating the latch cam in a direction that is opposite to a direction of rotation of the blade.
2. The method of claim 1 , wherein the act of applying the opening force comprises applying a torsional force to the blade.
3. The method of claim 1 , wherein the act of applying the opening force comprises applying a force to the blade using a torsional spring.
4. A folding knife comprising:
a blade having a first recess and a second recess offset from said first recess;
wherein said first recess is configured to receive a pivot pin, and the blade is configured to rotate about an axis of the pivot pin;
wherein said second recess is configured to receive a latch cam;
wherein said latch cam comprises a body and an offset pin;
wherein said latch cam body is located substantially within said second recess, and said offset pin is located substantially external to said second recess;
a spring mechanically coupled to the offset pin and configured to exert a force on the offset pin in a direction of blade opening.
5. The knife of claim 4 , comprising a reference piece having an arcuate slot with a convex extension slot positioned at one end of the arcuate slot.
6. The knife of claim 5 , wherein the latch cam is arranged to rotate in said blade to move the offset pin from the convex extension slot to substantially within the arcuate slot.
7. The knife of claim 5 , wherein the reference piece comprises a liner.
8. The knife of claim 5 , wherein the reference piece comprises a handle.
9. The knife of claim 5 , wherein the offset pin is positioned substantially in the convex extension slot when the blade of the knife is rotated less than a predetermined angle.
10. The knife of claim 5 , wherein the force exerted by the spring on the offset pin is substantially impeded by at least one wall of the convex extension slot.
11. The knife of claim 5 , wherein the offset pin is positioned substantially in the arcuate slot when the blade of the knife is rotated greater than a predetermined angle.
12. The knife of claim 5 , further comprising:
a flipper positioned on a side of the knife opposite a side from which the blade is removed, the flipper configured to receive an external force that at least partially rotates open the blade.
13. The knife of claim 12 , wherein the flipper comprises a protrusion on the knife extending through the side of the knife opposite the side from which the blade is removed.
14. The knife of claim 12 , wherein the blade opens substantially under the force of the spring when an edge of the flipper is flush with or above an edge of a knife handle.
15. The knife of claim 5 , wherein the spring substantially rotates the blade to a fully open position when the offset pin is positioned substantially within the arcuate slot.
16. The knife of claim 4 , further comprising a stud mechanically coupled to the blade and configured to receive an external force that at least partially rotates open the blade.
17. The knife of claim 4 , wherein the spring comprises a torsional spring wound around a pivot axis of the blade.
18. The knife of claim 4 , wherein the spring comprises:
a first spring positioned to a left of the blade; and
a second spring positioned to a right of the blade.