Cutting tool with blade and handle opening control mechanism
A bypass pruning tool with a manual dial adjustment for varying the degree of blade and handle opening. A rotary drum dial uses a nautilus cam with a shaft cam-follower to provide adjustment of the blade and handle openings in a continuous range. A blade locking mechanism provides position closure of the blades.
1. A cutting tool with a blade and handle opening control mechanism, comprising:
a first blade attached to a first handle, with an axis of rotation between the first blade and the first handle, a travel ridge on the first blade adjacent to the first axis of rotation;
a second blade attached to a second handle, with an axis of rotation between the second blade and the second handle, the second blade rotatably joined to the first blade at the first axis of rotation;
a drum dial located on the second blade with an axis of rotation perpendicular to the axis of rotation of the first and second blades, the drum dial having an interior surface with grooves parallel to the drum dial axis of rotation;
a cam cylinder having a nautilus cam surface on one end of the cylinder and ridges on the outside surface of the cylinder sized to mate with the grooves on the interior surface of the drum dial, the cam cylinder located in the drum dial for rotation with the drum dial; and
a cam follower engaging the nautilus cam surface on the cam cylinder, and riding on the travel ridge on the first blade.
2. The cutting tool of claim 1 further comprising:
a hub located in the interior of the drum dial, the hub having detent fingers engaging the grooves in the interior surface of the drum dial, whereby rotation of the drum dial moves the detent fingers from one groove to another and rotates the nautilus cam surface.
3. The cutting tool of claim 1 wherein the drum dial has setting markings on an outside surface, each setting mark corresponding with a certain open angle of the first and second blade.
4. The cutting tool of claim 1 further comprising a blade lock shaft on the first handle adjacent to the axis of rotation, the second blade having a blade pivot head at the axis of rotation with a cavity in the blade pivot head aligned with the blade lock shaft when the first and second blades are closed, whereby sliding the blade lock shaft into the cavity of the blade pivot head cavity prevents the blades from rotating with respect to each other.
5. The cutting tool of claim 1 further comprising a spiral spring fastened to the first handle and second handle below the drum dial, whereby the spring tends to move the blades and the handles apart.
6. The cutting tool of claim 1 wherein the first and second blades are bypass cutting blades.
7. The cutting tool of claim 4 further comprising a knob on the blade lock shaft for moving the shaft into and out of the cavity on the blade pivot head.
8. The cutting tool of claim 3 wherein the setting markings on the drum dial are Arabic numbers.
9. The cutting tool of claim 8 further comprising a stop mechanism in the drum dial for preventing the drum dial from rotating beyond the lowest and highest number markings.