Technology of watch production - part 82

C h a p t e r IX

FINISHING OPERA TIONS

Finishing operations occupy a prominent place in watch production.

'.ilfatch-movement parts are ground, lapped and polished in order to reduce
friction and increase their resistance to corrosion . External parts (cases ,

dials and hands ) are subjected to finishing operations designed to give them

an aesthetic appearance and to make them resistant to light, wear and cor
rosion. The complex of finishing operations includes grinding, lapping and

polishing as well as electroplating and chemical and varnish coating. Steel

parts of the watch movement are subjected to heat treatment (hardening and

tempering) before being ground and polished . Hardening and tempering con

ditions for typical watch parts are given in Table 1 . Parts made of non

ferrous alloys are s ubjected to additional mechanical, chemical and electro

chemical proces sing before being coated .

TABLE 1

Hardening and tempering conditions for typical watch parts

Hardening

Tempering

Part

Grade of

hardness ,

time,

hardness,

steel

temper-

time,

temper-

ature, oC

min

HRc

ature,

min

HRc

Balance staff

•

UlOA

780- 790

63- 65

1 8 0-190

59-61

Barrel arbor . . . . . . . . . .

UlOA

780- 790

63-65

200-210

56-58

Cannon pinion . . . . . . . .

UlOA

780- 790

63-65

350-400

1 0

49-52

W inding wheel and keyless

wheel . . . . . . . . . . . . .

UlOA

780- 790

63- 65

200-210

56-58

Escape wheel . . . . . . . . .

UlOA

780-790

63-65

280-290

1 0

53-55

Pallet lever . . . . . . . . . .

UlOA

780-790

63- 65

280-290

53-55

Regulator

. .

UlOA

780-790

63- 65

280-290

1 0

54-56

Hour-setting and winding

lever

. . .

. .

U10A

780- 790

63-65

200-220

56-58

Pinions

. . . . . . . . • . . . .

U7AV 8 00-820

62-64

280-300

52-55

Screws

•

U7AV

800-820

62-64

330-340

47-50

Pallet arbor

. . . . . • . . . .

U7AV

800-820

62�64

200-210

1 0

56-58

GRINDING, LAPPING AND POLISHING OF STEEL PARTS

The working surfaces of steel parts , such as the journals of pinions and

staffs (must have, at least, a class 1 2 finish in order to reduce friction in

the watch movement to a minimum. The outer s urfaces of the parts (the

faces of s c rew heads, the upper faces of the keyless and escape wheel s ,

3 2 5

the regulators, etc . ) must be finished to surface - quality class 1 1 - 1 2 at
least, in o rder to give the parts an aesthetic appearance and to make them

corrosion-resistant .

Grinding, lapping and polishing of the parts after hardening and temper

ing gives them the surface- finish quality required . The first two are pre

paratory operations which precede polishing and impart a class 8 or 9

surface-finish quality.

Pinions and staffs turned in automatic machines have a class 8 or 9 sur

face-finish quality and therefore need no additional stages prior to polishing.

Certain flat parts , such as keyless wheels, hour- s etting and winding

levers , are ground in o rder to level their faces and remove burrs resulting
from blanking.

Polishing removes microroughness 0 . 2 5 to 3.2

high from machined sur

fac e s .

Polishing i s classified as being dimensional or decorative . Dimensional

polishing has the dual aim of providing a class 1 1 to 1 3 s urface finish and of
bringing the dimensions within the required tolerances , Decorative polish

ing, or buffing, is applied to impart an aesthetic appearance to the parts .

Although no dimensions are specified in decorative polishing, the thickness

of the metal layer removed must lie within the tolerance limits on the part

dim ens ions .

The grinding, lapping and polishing methods used in watch production

are extremely divers e and depend both on the dimensions and shape of the

machined part and on s urface - finish requirements . The abrasives us ed are

also very diverse.

Lapping and polishing flat steel parts .

Flat parts are lapped and polished

on the S - 1 5 two- spindle vertical machine (Figure 1 ).

The machine consists of a base , inside of which an electric motor is

mounted, a bed with a round table and c ontrol me chanism, and a support

which carries two spindles . The electric motor drives the round table and

the machine spindles (Figure 2 ) through gears ( 1 - 2 - 3 - 4 - 1 0- 1 1 - 1 2 - 1 3 ) and

( 1 - 2 - 3 - 4 - 5 - 6 - 7 - 8 - 9 ) respectively .

The gears ( 1 1 ) and ( 1 3 ), fitted freely on a shaft, transmit rotation to

the round table through a draw key, by means of which two speeds of rota

tion can be imparted to the machine table .

The duration of operation is adjusted by means of a special device. The

gears ( 1 4 ) and ( 1 7 ), which are part of a planetary train, are mounted on the

same shaft with gear ( 1 0 ). The planet gears ( 1 5 ) and ( 1 6 ) are rigidly inte r

connected by a bushing and fitted on a shaft fixed to gear ( 1 0 ). One revolu
tion of gear ( 1 0 ) corresponds to 0. 00037 revolutions of the shaft carrying

the spiral gear ( 1 8 ), and therefore to 0. 00037 revolutions of the shaft car

rying the spiral gear ( 1 9 ) . If

n =

9 0 rpm for gear ( 1 0), gear ( 1 9 ) will re

volve at 0 . 03 3 rpm ( 1 / 3 0 rpm ), as can be calculated using the planetary

transmission formula for one revolution of gear ( 1 0 )

1 -.

0,00037.

The shaft which carries gear ( 1 9 ) also has a jaw clutch ( 2 0 ), on whos e

left elem ent the pin (2 1 ) i s fastened. When shaft and clutch revolve, the

pin (2 1 ) approaches the stop (2 2 ) and lowers it. The stop (22 ) is thus made

to act on a micros witch which stops the electric motor, and thus the machine .

3 2 6

-.J

FIGURE 1 . S-15 two-spindle flat
surface lapping machine

;To

rpm

FIGURE 2. Kinematic scheme of the S-15 machine

The time of continuous operation of the machine can be adjusted between

0 . 5 and 3 0 min by suitably positioning the clutch jaw with the pin (2 1 ) relative
to stop (22 ).

Technical data, S - 1 5 machine

Table diameter, mm

•

. . . . . . . . . . . . . • . •

. 240-320

Maximum block diameter, mm

•

• •

•

Table speeds, rpm

. . . . . • .

•

. . . . . . . . . •

60, 120

Spindle speed, rpm

• .

. .

. •

•

1 92

Distance between spindles, mm

•

. .

150

Number of blocks set simultaneously

•

. .

. •

Electric motor

•

. • . . . . . . . . . . . . •

1 kw

1440 rpm

The parts to be lapped and polished are fastened to the blocks us ing rosin

or shellac . The blocks are cast- iron disks 4 0 to 50 mm in diameter and

2 . 5 to 6 mm thick, having reces s e s of various shapes into which the parts

to be machined are placed.

The design of a block for lapping and polishing of s crew heads is shown

in Figure 3 . There are spaces for 1 00 to 5 0 0 s c rews i n the block.

The screw shank fits into a hole , and the head is supported on the flat or
conical face of the hol e . The screws are loaded into the blocks by the S - 1 4

machine (Figure 4 ) .

Type I

Type

lil

FIGURE 3. Holding bloci< for lapping

and polishing of screw heads

FIGURE

S-14 machine

for

setting screws into

holding blocl<s

The block is placed in the machine funnel ( 1 ) and screws are poured from

above . The funnel vibrates , and the s crew s hanks enter the block holes .

The air below the block is evacuated by a fan in order to facilitate the setting

of the s c rews into the holes. The funnel body (2 ) is mounted on the connect

ing arm ( 3 ) and held in a vertical position by the pin (4 ). A reciprocating

3 2 8

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