Box knife

A knife comprising a handle having sides, upper and lower surfaces extending between the sides, and front and rear ends;

• a flat blade mounted within the handle such that a segment of the blade projects from the front end of the handle, the segment having a cutting edge which is located generally beyond the lower surface of the handle, whereby the knife may be grasped at its handle, and with the handle leading, its blade may be drawn through an object to be slit;
• guards mounted on the handle to pivot about an axis that is located above the cutting edge and is perpendicular to the plane of the blade, there being one guard on one side of the blade and another on the other side, the guards being rotatable about the pivot axis between an extended position wherein the projecting segment of the blade is shielded and a retracted position wherein the projecting segment is exposed for cutting purposes, the extended position for the guards being located ahead of the retracted position relative to the handle, so that the guards in moving from their extended to their retracted positions pivot rearwardly with respect to the handle, the guards having curved edges which are presented away from the pivot axis and are in the region of the cutting edge when the guards are extended, the curved edges being configured to roll along a surface of the object to be slit and to thereby cause the guards to move to their retracted position as the blade penetrates the surface under a force exerted on the handle;
• and means on the handle for preventing the guards from pivoting forwardly beyond the extended position.

A knife comprising:

• a handle having ends;
• a blade having a cutting edge;
• means on the handle for positioning the blade such that at least a segment of the blade and its cutting edge projects beyond one end of the handle;
• and guards mounted on the handle at both sides of the blade, and being rotatable about an axis that is offset from the cutting edge of the blade so as to move between extended and retracted positions, but being biased toward the extended position, the guards when in the extended position being located to the sides of the segment of the blade that projects beyond the end of the handle and further projecting beyond the cutting edge on the segment of the blade that projects beyond the handle, whereby the blade and its cutting edge are normally shielded when the knife is not in use, the guards when in their retracted position permitting the projecting segment of the blade and its cutting edge to be exposed for cutting purposes, each guard being somewhat triangular in shape in that it has generally three corners, including an upper corner at which the pivot axis is located, a curved front corner which is located generally directly beyond the end of the cutting edge when the guard is in its extended position, and a rear corner which, when the guard is in its extended position, is located near that end of the handle from which the blade projects, there also being on each guard margins located between the corners, including a convex front margin between the upper corner and the front corner, a convex lower margin between the front corner and the rear corner, and a rear margin between the rear corner and the upper corner, the front margin being curved with the cruvature of that margin being less than the curvature of the front corner and with the front margin merging into the front corner.