Screw capable of reducing drilling torque
A screw capable of reducing drilling torque includes a shank provided with cutting threads, and a head and a drilling portion respectively formed at two ends of the shank. Each cutting thread has two opposite flank surfaces converging at a thread crest. On the thread crest are recessedly formed notches alternating with grooves. Each groove has an upper crest edge and a lower crest edge meeting the flank surfaces respectively. Each notch has a first cutting edge and a second cutting edge meeting the flank surfaces respectively. The above cutting edges and crest edges cooperate to provide multiple cutting points, thereby increasing the cutting efficiency, preventing the improper entanglement of fibers, and reducing drilling torque for easier screwing. The notches and grooves accommodate and press partial debris for achieving a stable and tight engagement between the screw and an object and increasing the ability of resisting the pulling-out force.
1. A screw capable of reducing drilling torque comprising a shank, a head disposed at one end of said shank, a drilling portion disposed at another end of said shank and opposite to said head, and a plurality of cutting threads spirally disposed on said shank, wherein each of said plurality of cutting threads includes an upper flank surface, a lower flank surface opposite to said upper flank surface, and a thread crest formed at a convergence of said upper and lower flank surfaces;
wherein a plurality of notches cut in said thread crest, to thereby define a plurality of spaced apart crest portions between two adjacent notches, a plurality of grooves being recessedly formed on said plurality of crest portions to thereby allow each of said grooves to form an upper crest edge and a lower crest edge which meet said upper flank surface and said lower flank surface respectively, said plurality of notches and said plurality of grooves being cross-sectionally arranged in alternation, each of said plurality of notches having a first cutting wall with a first cutting edge meeting both of said upper and lower flank surfaces and a second cutting wall with a second cutting edge connected to said first cutting edge, said first cutting wall and said second cutting wall converging at a root.
2. The screw as claimed in claim 1 , wherein said upper and lower flank surfaces of said cutting threads lie in a form of alternate rises and falls to allow said cutting threads to be in a wavy arrangement.
3. The screw as claimed in claim 1 , wherein each of said grooves recessedly formed on each of said crest portions has two ends extending into two adjacent notches respectively and reaching said roots of said two adjacent notches to thereby define an extensive space, two adjacent grooves being connected to each other by said extensive space.
4. The screw as claimed in claim 1 , wherein said first cutting edge of each of said notches and a second cutting edge of an adjacent notch meet at a point from which a reference line is defined, said first cutting edge and said second cutting edge of each of said notches respectively sloping with respect to said reference line at a first cutting angle and a second cutting angle, said first cutting angle and said second cutting angle being different.
5. The screw as claimed in claim 1 , wherein said groove defines a baseline passing through a center of said groove and normal to an axis of said shank, said upper flank surface sloping with respect to said baseline at an upper flank angle, said lower flank surface sloping with respect to said baseline at a lower flank angle, said upper flank angle and said lower flank angle being different.
6. The screw as claimed in claim 1 , further including a plurality of auxiliary threads spirally disposed on said shank, said plurality of auxiliary threads being formed without said notches and said grooves.