Technology of watch production - part 30

the whole length of the thread . After completion of the chasing, the head

stock returns  to  its  initial  position.  Thread  tapping can  be  combined with
cut- off,  but  only in the  initial  cut- off  s tage  while  the  part  is  s till  rigidly
connected to  the  stock.

The spindle speed necess ary for chasing the thread is determined with

the aid of Table 3 , which gives the ratio between the chas e r spindle speed

and the machine spindle speed for the cutting speed adopted. The highes t

ratio is specified when chasing brass , and the lowes t when tapping U 1 0A

steel. Inte rm ediate values are s elected in all other cases .

TABLE 3

Pulley diameters and the ratio of chasing die spindle

(n1) and the

working-spindle (n) speeds when chasing a right-handed thread

Ratio of spindle

Pulley diameters•

speed

n , : n

1 .1 2 : 1

1 .24: 1

5 0

4 5

1 .35: 1

1 .46: 1

• For the belt position see Figure

2 1 .

The cutting speed is determined from the formula

7t · d ch

(n1 - nl

v =

1000

1 5 0

165

180

1 95

( 1 )

The working- spindle speed

n ch,

necess ary to chas e a thread is deter

mined f rom the fo rmula

n ch

= Z

n1 -

ii•

where

the numbe r o f thread turns ·

(2 )

Let us dete rmine the value of

ch ,

necess ary for chasing a thread on

the winding- key s haft (see operation sheet on pp . 1 38 - 1 3 9 ).

A s sume

n =

5 5 5 0 rpm , and let the m ate rial be U 7A V s teel . We s elect

from Table 3 the ratio �

1 . 1 2 and thus obtain

5 5 5 0 X 1 . 1 2

6 2 1 6 rpm .

'lt· l . 2 (6 2 1 6 - 5 5 5 0 )

The cuttmg speed w1ll be

v =

1 000

�

5 m /mm.

The numbe r of revolutions necess ary for chasing seven thread turns on

the winding-key shaft will be (taking into account the approach of the chaser

and the run- out )

nch

= 58

revolutions .

In addition the uns crewing of the chas ing die requires

nuns=

7 .

1 2 revolutions ':' .

• The absolute value is taken in the calculation.

1 1 7

In all 58 + 1 2

7 0 revolutions are required and this value is noted on the

operation sheet. The uns c rewing takes place at a chasing spindle speed of

, _ 6 2 1 6 X 4 5

- 1 8 7 5 rpm .

( n1 -

1 50

1 8 7 5 ) .

S l o t t i n g . Screw heads , bushings and rollers are slotted using a spe

cial attachment mounted ho rizontally on the bed (Figure 2 2 ).

FIGURE

22 .

Slotting

1 -lever; 2-pick-up bushing; 3-flap; 4-milling cutter; 5 -knock-out cleat; 6-trough; ?-plate cam;
8-bell (edgewise) cam; 9-pin.

The slotting operation is carried out as follows . Just before cut- off the

lever ( 1 ) takes up a position with the hole in the pick-up bushing directly

opposite the part. The lever ( 1 ) is then moved along the bar axis by the

bell cam, the bushing (2 ) is slid over the part and, when cut- off is completed,

the lever, together with the part, takes up a new position opposite the slot
ting cutter ( 4 ) . The flap ( 3 ) prevents the part from falling out of the bushing

during its transport.

A c am advances the part into the slotting cutter .

The slotting- cutter spindle i s powered from the stud shaft IX (Figure 5 ) .

When the slotting has been completed, the lever ( 1 ) returns to its initial

pos ition, and the pin ( 9 ) in the pick-up bushing ( 2 ) contacts the cleat ( 5 ) and

ejects the p art into the trough (6 ). A ll motions of the lever ( 1 ) are control

led by the flat and bell cams ( 7 ) and (8 ), mounted on the camshaft .

When the slotting attachment is in operation, slides Nos 3 and 4 do not

operate . Slide No . 3 is taken out of the tool head together with the b racket.

The flap ( 3 ) is attached to slide No 4 .

D i a m o n d k n u r 1 i n g i s accomplished by knurling roll ers in a holder

mounted in slide No . 4 o r No . 5 ( Figure 2 3 ).

A longitudinal feed is us ed for knurling in order to prevent bending of

the blank by radial stresses . The width of the knurling roller is , in this

cas e , several times small er than the l ength of the surface to be knurled.

B r o a c h i n g o f h o

e s o f s q u a r e a n d o t h e r s h a p e s is car

ried out using a b roach chucked in the drilling- attachment chuck (Figure 2 4 ) .

1 1 8

The b roach rotates freely in the chuck and is fed toward the work by a

spring, as in drilling. As the b roach contacts the work, it is gripped by
the rotating bar and rotates at the speed of the latter .

FIGURE 2 3 .

Knurling-tool configurations

FIGURE 24.

Chucking of a broach

in the

drilling-attachment spindle

The b roach must be accurately centered relative to the p reviously drilled

hole in the work. The chuck and spindle of the drilling device do not rotate

during b roaching.

B a c k d r i l l i n g. This term refers to the drilling of a hole in the cut

off side of the part. To this end two attachments are mounted on the ma
chine . One of the attachments is mounted in place of the milling attachment

and the other is mounted behind the tool head and above the heads tock. The

firs t attachment feeds the p art unde r the drill while the s econd rotates the

drill. The spindle of the s econd attachm ent is driven from the s tud shaft lX

(see Figure 5 ). Figure

c is an example of a back-drilled part.

T a p e r s w i t h a n g l e s o f 3 to 5° are turned with the us e of a special

attachment mounted on the bed ways (Figure 2 5 , a ) . The attachment in

creases the trans miss ion ratio of the rocker levers from 3: 1 to 1 0 : 1 (the

ris e transmitted from the cam to the rocker tools is reduced by a factor

of up to 1 0 ) . A s a result, small inaccuracies i n the cam p rofile do n o t in

influence the accuracy of the proces s . The most c ritical ope rations , with

tole rances of 0 . 003 to 0 . 005 mm, are performed by the rocker tools with

the aid of this attachment .

The attachment is usually used in combination with an undercutting at

tachment (Figure 2 5 , b ), the two attachments being mounted on a common

base ( 1 ).

Two followers ( 3 ) are located at one end of the lever (2 )

One of the

followers works with cam (4 ) intended for turning, and the other with cam

(5 ), designed for plunging and undercutting. The lever rotates about axis (6 ) .

The p i n ( 7 ) is located a t the opposite end of the lever and acts o n the pin

of the shoe ( 8 ), which is mounted directly in the rocker. Pins ( 7 ) and ( 8 )

1 1 9

drop when the profile of cams ( 4 ) and

( 5 )

ris es , and as a result tool No. 1

retracts .

The undercutting attachment consists of a rigid plunger rod ( 9 ), mounted

in the hinge mount ( 1 0 ) . The mount is carried on the slide ( 1 1 ) .

10 15

FIGURE 25. Attachment for reducing rocker travel and for recessing

The carriage is fed l ongitudinally by the cam ( 1 2 ) through the lever ( 1 3 ) .

The cutter is held i n the collet o f the rod ( 9 ) b y the pin ( 1 4 ). The s c rews ( 1 5 )

and ( 1 6 ) se rve for c entering the rod in the vertical direction, and the s c rew
( 1 7 ) for setting the slide in the transve rs e direction.

The brief descriptions given above of operations performed illustrate the

great versality of Swiss - type automatic s crew machines which can be fur

ther broadened by the introduction of a fourth vertical slide and a third ho

rizontal slide.

Only parts of extrem ely complex configuration, however, require this

extra degree of versatility.

CUTTING CONDITIONS

The range of cutting speeds on the automatic s crew m achines is relative

ly narrow: from 2 0 to 60 m /min when machining s teel, and from 30 to

1 00 m /min for machining bras s .

The low cutting speeds are due to the s mall m achining diameters and to

the fact that when working at maximum spindle speed the machine vibration

1 2 0

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