THREAD CUTTING 1. Threads available from the gearbox The screwcutting dial on the apron has four numb- ered divisions and four sub-divisions marked on its suFface, clearly visible from the operating position. The housing carrying this dial is located to the side of thg apron and is retained in position by a knurled handscrew. When not required for use it may be swung out of contact with the leadscrew, since it is only employed when screwcutting is actually carried out. To cut an even number of threads per inch (e.g. 12 t.p.i., 14 t.p.i.) the leadnut may be engaged at any division on the dial. For cutting an odd number of threads per inch (e.9.
13 t.p.i.) the leadnut must be engaged only on the numbered divisions. For frac- tional threads (e.9. a* t.p.i.) the leadnut must only be engaged at the division marked 1 on the dial. When engaging the leadnut, care should be taken to ensure that the appropriate dial division coincides exactly with the fixed point on each pass. The settings of gear box levers for the threads avail- able from the gearbox are shown on the machine data plates which are reproduced below Example It is required to cut 27 t.p.i. The values of X and Y may be chosen from any of the relevant numbers given above; and there is no rule about the choice.
lf the values selected give impossible numbers of teeth, try other values of X and Y and continue so doing until a practicable result is obtained. Setting up gear train (27 t.p.i.) 1. Remove gear f rom headstock spindle. 2. Loosen swingframe (quadrant) locking nut located between swing frame and end of bed. Swing quadrant until 120T idler gear is out of mesh with gear on gearbox shaft (A). 3. Loosen idler gear stud nut located on inside of quadrant, slide 120T idler gear away from head- stock spindle. 4. Select the proper gear for headstock spindle position (i.e. 32T as example). Place gear in posi- tion on spindle and secure in place, 5.
Slide 120T idler gear up until properly meshed with gear on headstock spindle and secure in place, For correct mesh; place piece of heavy wrapping paper ('005 in. thick) between teeth of meshing gears, tighten gears in position and remove paper. 2. Threads not available from the gearbox To cut special and multi-start threads which are not immediately available from the gearbox, it is neces- sary to use special change gears which are obtainable as extra equipment. For calculating the number of teeth in the required gears the following formula should be used: Threadto becut : 3 x X x Y : Drivergear 1 4 x T D r i v e n g e a r Where X : hole in feed box Y :
1 with selector levers on A C 2 with selector levers on A D 4 with selector levers on B C 8 with selector levers on B D and T : Number of threads per inch to be cut 6. Check gear in position on gearbox spindle. For obtaining 27 t.p.i. it should be 42T gear (B), 7. Swing quadrant so '120T idler gear is in proper mesh with gear on gearbox shaft. Tighten in place. 8. Set gearbox levers properly, as shown on the dita plate (left hand to C, right hand to B) and position tumbler to cut 24 t.o.i. Values for X are as follows:- 9. Check gear set-up by cutting 27 t.p.i. on scrap stock, In the case ol27 t.p.i.:
3 x 24 x 4_32_Driver 14 x 27 42 Driven 0 28 0 0 0 0 0 0 0 26 24 23 22 2A 19 18 STIDING FEEDS IN II{CHES.SURFACING sLlDrl{G D B il2 t04 96 92 88 80 76 72 64 . 0 0 t 7 .00 t8 .00 t9 .002 .0022 .0024 0025 '0027 .003 c B 56 52 48 46 44 40 38 36 32 .0033 .0035 .0038 .004 .0043 .0047 .005 '0053 .006 D A 28 26 24 23 22 20 t 9 r 8 t 6 .0c6s .007 '0075 .008 .0085 .0095 . 0 1 0 '0 r05 .0 r2 c A l 4 t3 t2 il* t l t 0 e+ 9 8 . 0 t 3 .0 r4 .0r5 . 0 t 6 .0t7 .
0 l 9 .020 '021 .024 WHEN USING 55' DRIVER GEAR c A 7 6L 6 s* s* 5 4z 4L 4 .027 '029 .03 | .032 .035 .038 .040 .042 -0,+8 LEVERS THREADS PER II{CH \ FILL WITH SHELL TELLUS OIL 33 TO MARK ON SIGHT GLASS \ OIL OBTAINABLE FROM SHELL OIL COMPANIES THROUGHOUT THE WORLD /