Technology of watch production - part 39

The diameter of the collet hole is equal to the nominal diameter of the

bar with the tolerance of class 2 accuracy suitable for a close running
fit . The use of collets having slightly different dimensions is not recom

mended as an additional run- out appears as a result of the incorrect grip
p ing of the bar stock and the collet rapidly loses its sp ring p roperties . The

collet has brazed carbide inserts which increas e its durability 4 - 5 tim es .

C ollets with carbide inserts are slotted by m eans of diamond cutting disks .

Twist drills . Left- hand twist drills are used on Swiss -type automatics .

The types and dimens ions of the twist drills most frequently use d i n watch

p roduction are given in Tables 1 9 and 2 0 .

TABLE 19

Dimensions of straight-shank twist drills with

ground flutes, mm

Drill diameter

nominal di-

tolerance

Inension

0.025-0.30

-0.008

1 8

0.32-0.40

-0.0 1 0

0.42-0.50

-0.010

0.52-0.60

-0.01 0

0.62-0.70

- 0.01 2

0.72 - 0.80

-0.0 1 2

0.82- 1 .00

-0.0 1 2

1 0

TABLE 20

Dimensions of twist drills with ground flutes and

oversize straight shanks, mm

Drill diameter

nominal di-

Inension

tolerance

0. 1 0-0.20

- 0.006

1 .5 - 2.5

1 5

0.2 1 -0.30

-0.008

2.5-3

1 5

0.32-0.40

- 0.0 1 0

1 8

0.42- 0.50

-0.0 1 0

0.52-0.60

- 0.0 1 0

0.62-0.70

-0.01 2

0.72-0.80

- 0.012

0.82 - 1 .00

- 0.012

Drills with o ve rs ized shanks make it pos s ible to reduce the number of

collet dimensions . Because of the s m all diameters of the drills , the helical

flutes , having a particular c ontour, are ground from the hardened blank / 1 2 /

The tole rance o n the working diameter is according t o accuracy class

2 a':' of GOST 3 04 7 - 54 . The drills are made of type R 1 8 high-speed steel

with a hardness Rc= 59 to 6 2 .

U 1 0A - U 1 2A steel i s not us ed for d rills as the drills are heated by the

grinding wheel (when the flutes are ground), and this would cons iderably

reduce the hardness of drills made of these steels .

Taps .

Watch m echanisms us e right- hand, and sometimes left- hand,

threads of diameters from 0 . 3 to 2 . 6 mm. The thread-profile angle is 50°,
for threads of 0 . 3 - 0 . 9 mm diam eter, according to GOST 3 1 96 - 4 6 , and 6 0°

for watch th,reads of larger diameters , according to GOST 7 2 1 7 . The 50°

p rofile has s e ve ral advantages over the generally used 6 0° p rofile for small

diameters . The s trength of the thread increases as a result of the increas e

• [A 1st accuracy class fit corresponds to an extra fine fit, a 2nd accuracy class fit to a fine fit, a 3rd accuracy

class fit to a plain fit, and a 4th accuracy class fit to a rough fit. ]

1 5 3

in its depth and the thread wear rate decreas es as a result of the increas e
in the flank area. A mong the sho rtcomings of 50° threads is a certain

weakening of the s crew or tap body as a result of the decreas e in the root
diam ete r.

The ove r - all length and the threading length of the taps used fo r thread

ing 0 . 3 - 0 . 9 mm diameter threads are different from thos e generally ac

cepted (see Table 2 1 ).

TABLE 2 1

TABLE 22

Dimensions and shape of triangular taps, mm

Dimensions of three-flute taps,

111111

0.3

0.075

1 6.8

2.6

0.5

0.1

0.35

0 .075

1 6.8

2.6

0.5

0 . 1 2

0.25

27.7

1 .5

0.40

0 . 1 00

18.8

3 5

0.6

0. 1 5

1 .2

0.25

27.7

0.45

0. 1 00

18.8

3.5

0.6

0 . 1 7

1 .4

0.30

1 0

1 .75

0.50

0 . 1 25

20.9

0.75

0.2

0.55

G . l 25

20.9

0.75

0.22

1 .7

0.35

1 2

0.60

0. 1 50

20.9

0.85

0.25

2.0

0.40

1 4

2.3

0.70

0. 1 75

20.9

0.25

2.3

0.40

1 4

2.3

0.80

0.200

23.0

0.30

2.6

0.45

1 6

0.90

0.225

23.0

1 .3

0.30

Triangular taps track reliably into the hole, have a s mall cutting-lip

width, and are stronge r than taps of the usual s hap e . Their s hortcoming
lies in their large negative rake angles , as much as 4 0° at the m ajor dia

meter, and 7 0° at the minor diameter. Cutting is replaced to a consider

able extent by s craping when these taps are used, and this requires an ad

ditional effort.

Triangular taps have insufficient clearances for chip removal and s uch

taps are therefore not used for threading holes of a diam eter larger than

1 mm in brass and steel , nor holes with a depth greater than 1 . 5d.

Three - flute taps are us ed for threads of diameter larger than 1 . 0 mm and

depth m o re than 1 . 5d . The dimensions of thes e taps are given in Table 2 2 .

The three - flute taps have zero rake angles and this gives considerably

improved cutting conditions as compared with the triangular tap s .

The flutes als o provide s ufficient chip space .

1174

1 54

The b ody s ection of three -flute taps is somewhat weakened and it is more

difficult to mill the flutes in these taps than in the triangular taps . Three
flute taps are made from U 1 OA - Ul2A s teel .

Chaser dies .

Three standard types o f chaser dies are us ed i n watch

production: round , nonadjustable , thread-forming tools without chip spaces
for cutting threads of 0 . 3 - 1 .2 mm diameter; tubular adjustable chasing dies

with chip spaces for cutting threads of 0 . 3 - 1 . 7 mm diameter; and round,

nonadjustable dies with chip spaces for cutting threads of 1 . 0 to 2 . 6 mm dia
meter.

The round,nonadjustable dies without chip spaces are flat disks with

tapped holes (see Table 2 3 ).

TABLE 23

TABLE 24

Dimensions of round dies without chip spaces, mm

Dimensions of tubular dies,

m m

0.3

O.D75

0.35

0.60

0. 150

0.60

0.35

O.D75

0.35

0.70

0.175

0.60

0.40

0.1 00

0.35

0.8

0.200

0.60

0.45

0.100

0.35

0.9

0.225

0.70

0.50

0.1 25

0.40

1 .0

0.250

0.90

0.55

0. 1 25

0.40

1 .2

0.250

0.90

0,30

0,075

0.5

0.70

0.175

0.35

0,075

0.5

0.80

0,200

0.40

0.100

0.5 0.90

0.225

0,45

0.100

0.5

1 .00

0.250

0.50

0. 1 25

0.5

1 .2

0.250

6.5

0.55

0, 125

1 .4

0,300

0.60

0,150

1 .7

0,350

1.4

1.6

1 .6

The die hole is chamfered at both ends and its thickness must not exceed

three thread pitches . The depth of the chamfer is 0 . 7 5 s and the cutting and

calibrating portions of the die are equal in length.

An increase in the thickness of the die leads to the s wift wors ening of the

threading conditions, to j amming of the part in the die and to breaking off

of the part.

A notch is cut on the end plane of the die to ameliorate the conditions of

thread formation. The s ervice life of thes e dies is not long (400 to 6 0 0

threads ), but their manufacture is simple . The blanks for them are stamped
from a s trip .

The tubular, adjustable dies are mainly used for threading in specialized

automatic machines . Their dimensions are given in Table 2 4 .

Tubular dies have three cutting lips with positive rake angles . The

threads are cut, and not formed as by the first type of die . The dies are
adjustable , which is particularly important when the mechanical properties

1 5 5

o f the bar stock are not uniform . When the lips dull they can be res harpened
by grinding the faces, and if the part being threaded breaks it can be re

moved from the die by removing the adjusting ring and forcing the lips apart.

A die without chip spaces must be dis carded in s uch a cas e . The s ervice

life of tubular chasing dies is 5 - 6 times longer than that of the forming dies ,

but their production requires s everal tim es more labor and mate rials . The

adjustable chasing dies are better than the forming dies for use in mass

p ro duction .

Round die s , nonadjustable but with chip spaces , are us ed for cutting

threads of 1 mm diameter and larger. Their advantage relative to the dies
without chip spaces lies in the pres ence of three cutting faces with positive

rake angles and with windows for chip removal (see Table 2 5 ).

TABLE 25

Dimensions of round dies, mm

0.25

2.0

1 .2

0,25

2.0

1 .4

0.30

2.5

1 .7

0.35

2.5

2.0

0.40

3.0

2.3

0.40

3.0

2.6

0.45

3.0

Round dies with chip spaces are more expensive to p roduce than are

those without chip spaces; however, they can be resharpened by grinding

the cutting faces . The dies are manufactured from U 1 2A and 9KhS, steels .

Slotting cutters .

Table 2 6 gives the dimensions of the slotting cutters ,

m ade of U 1 0A , U 1 2A , 9KhS steel s , used for slotting s crew heads and cutting

s m all slots in bushings and other parts .

Measuring instruments .

The outer diameters and l engths of the m achined

parts are m easured by micrometers of special design . Dim ensions with

tolerances of 0 . 02 mm and larger are meas ured by the horizontal L- 2 3 mi

crometer with divisions of 0 . 0 1 mm on the barrel and range from 0 to 15 mm

(Figure 34 ).

Dimensions with tolerances between 0. 003 and 0 . 03 mm are measured by

me ans of the c ombined instrum er.t K - 6 , consisting of an indicator with s cale

divisions of 0 . 0 0 1 mm and range ± 0 . 0 3 m m , and a micrometer head with

scale divisions of 0 . 0 1 m m , and range 0 to 1 0 mm (Figure 3 5 ).

1 5 6

Content .. 37 38 39 40 ..