Patent GB-707604-A (GB)
Title: A method of and apparatus for forming and threading the points of wood screws and the like
IPC: B21H3/06
Filed: 1951-10-11
Abstract: 707,604. Rolling screw threads ; threadmilling; turning wood screws. FRAY, V. H. Oct. 11, 1951 [Nov. 24, 1950; May 10, 1951], No. 23690/51. Classes 83 (3) and 83 (4) A method of forming and screw threading the points of wood screws and the like comprises the planetary travel of partially formed screws through rotary thread rolling apparatus with the shank ends projecting past the thread roller, and bringing the said projecting shank ends into contact with a rotating hob during -such planetary travel to cut the points and threads on such shank ends during passage past the hob. Partially formed screws 6 are fed along shoot bars 7, 7a to a passage 9 and are fed therefrom by a pecker 13 into the gap 5 between a grooved thread roller 2 and grooved. stationary segment. 4, passing between a spring loaded plate 11 with a grooved face 11b, and the grooved end face 4c of the segment. Disposed beneath the roller 2 and eccentric thereto is a hob 14 on a spindle 15, said hob having a cutter surface 14b, Fig. 4, formed with a two start helix 14c complementary to the thread to be formed on the point of the screw blank. The thread roller 2 and the oppositely rotating hob are driven in fixed relationship through gearing from a chain drive, and the pecker 13 is operated from a cam 29 rotated from the gear train. The pecker may be operated in the manner described in Specification 669,884. The surface of the roller, and the curved face 4a, and end face 4c of the segment 4, are knurled, roughened or serrated other than in the grooves to prevent the blanks from slipping. Preferably the threads are applied and the points cut in two stages by two machines, the hob 14 on the first machine which rolls the main portion of the thread having a plane cutter surface 14b with no helix, Fig. 3, and cutting a blunt tapered point 6b. The surfaces of the roller and the curved face 4a of the segment on the second machine are not serrated &c. and the angle of thread helix on either the roller 2 or the segment 4 is steeper than that on the other, the angle between the threads on the two being equal to twice the helical angle of the thread, so that a slight longitudinal travel of the screw is achieved during its planetary travel so as to avoid a junction mark between the rolled thread on the shank and the hobbed thread on the point. In a modification the two machines may be combined, Fig. 11 (not shown). Alternatively for lighter gauge screws of average hardness, the shanks are roll-threaded and the points formed and threaded in one operation in one machine, the threads on the roller and segment being arranged to effect a slight longitudinal travel, and the blanks being caused to enter the gap in correspondingly inclined positions by the pecker 13 and hinged plate 11. In a further modification the machine may function to form and thread the points of screws which have been thread rolled in a known manner and their ends left blunt, but preferably the ends are tapered during the shank thread rolling operation and the surface of the roller and the surface 4a on the segment are not then roughened &c.