END GEARING COMPUTATIONS.

 A number of threads may be cut, in addition to those shown on the standard and metric thread index plates, by using end-gearing in conjunction with the standard thread and feed gearbox.

 In order to facilitate such calculations as may be required, gear ratios are given for all threads shown on standard Index Plate, i.e. 3-92 T.P.I.

Threads per inch.

Rule:- select for trial, a gearbox ratio from those given on page 18, preferably one which would factorise easily.

Formula.( 1 ) ( Selected ) = Drivers
(Desired T.P.I.) ( Gearbox Ratio) Driven

Set the resultant gears on their respective studs; and gearbox to T.P.I. corrosponding to ratio selected.

Example:- Assume gears are required to cut 19 T.P.I.
Apply Rule:- Select for trial - 10 T.P.I. ratio 1/20 (Page 18)
Insert in Formula:- 1 x 1 = Drivers = Hd/stk. stud x Comp B
19 x 20 Driven Compound A Gearbox stud

Invert gearbox ratio to multiply 1 x 20 = Drivers
19 1 Driven
Factorise:- 1 x 20 = 10 x 2 = (10 x 2) (2 x 24) = 20 x 48
19 1 19 1 (19 x 2) (1 x 24) 38 24

 Place those gears on their respective studs in the order shown, and as per numerical thread Index diagram, using an idler if required. the direction of leadscrew rotation is controlled by Knob 6.

 Set gearbox as for cutting 10 T.P.I. noting at the same time that Knob 10 is correctly set at 'A', 'B' or 'C', in accordance with indication on thread Index Plate.

 By reference to diagram No.3 it will be noted that stud positions for the example quoted would be as follows:-

20 teeth gear on stud 12; compound 'A' & 'B' on stud 29; 24T gear on stud 11; and idler when required on stud 30; Interchanging of gears may of course be made in the orthodox manner.

Continued........