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479
SCREW


different ratios for screw-cuttin These a ain are doubled or] g 3 trebled by altering the ratios of other gears connected therewith, so § . . I — El ~s1 5 / Qi/".f4- "" 5 1 /' § § =' biifw" $- { QE ' /i ;//i Z A ' —'rf ” lf-»- E E /i ' E —' - 51 l0NDR£L § '. -X/"5/. ge, J /~ / '74, sg ee' "'532¢}. 1 eff#—~-. fm §§ - ~, . A /';§ ig § 5 E Luo scuw ' @' "-' ""' My § C , / D il Fig. 2. A, Simple train which rotates lead screw in opposite direction to mandrel, and makes slide rest feed away from the headstock. B, Simple train with intermediate wheel on stud, which rotates lead screw in same direction as mandrel, making slide-rest SCI'€W. feed towards the headstock. Intermediate on “stud" does not alter ratio. C, Typical compound train arranged for cutting a screw finer than that of the lead D, Ditto for screw coarser than that of the lead screw. that for each position of 'engagement of the stud wheel, two, or in some cases three, pitches can be cut. This avoids the waste of time involved in setting up fresh wheels on the swing-plate as often as a screw of different pitch has to be cut. Another step in the direction of economy depends on the removal of all screw-cutting, except those screws which are of several feet in length, from the ordinary lathe to the special chasing and screwing machines. The screw-cutting arrangement of an engineer's lathe is a cumbrous apparatus to fit up and set in motion for the cuttin of screws of small dimensions. When there was no other metilod available except that of common dies operated by hand or carried in a screwing machine, there was good reason why a true cutting tool should be operated in the lathe through change wheels. But the W y % °!:l'W / as 4

%”% reason no longer exists, since for the single cutting tool of the lathe the two or three 'cutters of the chasing and screwing machines (figs. 3 and 4) are substituted, and the hollow mandrel embodied in the latter permits of screws being cut and parted from the solid bars of several feet in length. Except for the cutting of long screws and screws of odd pitches, the ordinary lathe is now a wasteful machine. J e; . . géilrmng - rm! 5; I J aéeu l lg gliy » W .6, -| ° i '<?f'»§ ' G V "i*f5*§ if.'“f:: ~-~— - ~. i-E- ""?';:T:~'l§ lr:.;:;; *'— -~f5'?'i 5* Z ”“'1 ¢;';.1 J* éf"®~' ' -'rbi

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AML? ~ g g FIG. 3.-Bolt-Screwing Machine:(I ohn Stirk & Sons, Ltd., Halifax). lg, ged. B, Spindle. d J, Hdandle for opening the our-step b it p lley, riving ies. through triple spur gears D, K, Lever for automatically opento B. ing the dies, operating E, Opening die head. through ]., F, Bolt carria e racked to or fro L, Rod having adjustable dog b, 3. ilong tlilqe beg by rotation of and-w eel H, Handle for openinfg and closing vee-Jaws at a. or gripping and releasing bolts by means of a right- and left-hand screw. struck by carriage at a definite position of its travel, thus throwing the dies off the work. M, Pump drawing lubricant from reservoir in bed. The second method of cutting screws is that by means of hobs or leaders, and either comb or single-edged tools. That is, a short @ C,

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A . », e FIG. 4.-Opening Die-head for Screwing Machine. A, Spindle end. B, Sliding collar. C, Ring bolted to B, and enclosing ring having three coned E, Curledspring keeping chasers outwards in contact with a. F, Piece screwed to end of A, and provided with three grooves to carry the chasers. grooves tz, a, a, set eccentrically to close in or let out the G, Cover plate confining the chasers, and unscrewed from F when

chasers L). l changing chasers for other sizes.