Content .. 77 78 79 80 ..

Technology of watch production - part 79

The case backs of wate rproof watches have a more rigid s ection p rofile

and are threaded into the case middle. A P. V. C. sealing ring seals the

flange .

FIGURE 38. Two-spindle semiautomatic machine for chasing

of back

'\J\7\7\7 10

FIGURE 3 9. Buffing

the circumference
of the case back

(seventh operation)

The manufacturing process for wristwatch cases described above re

quires very diversified equipment and a relatively high labor expenditure

for a relatively low manufacturing accuracy. Design and production engi

neers are the refore striving to develop improved methods for machining

the case parts , which would reduce both the labor expenditures and the

material requirements . Some such methods are: pressure die - casting,

p recision casting, and stamping in hot or cold s tate . The blanks obtained

must be s uch that the only m echanical operations required are the finish

operations for the fitting dimensions , which have narrow tolerance.

T H E CASE MIDDLE O F POCKET WATCHES

The case middle of pocket watches has concentric projections and re

cesses in which the watch movement, the bezel and the back are fastened.

NMTsS 6 3 - 1 8 - 2 nickel silver, which is used in the m anufacture of the m iddle

is not sufficiently plastic for expanding operations . The middle is accordingly

blanked out of a 4 m m thick strip as a ring (Figure 4 0 ) . The blanks are de

greas ed, stres s - relieved and washed , and then rough-machined on m etal

cutting machines to produce a ring having the shape shown in F igure 4 1 .

While in wristwaches the winding-stem hole is obtained i n one operation,

as many as 18 operations are involved in making the winding- stem hole in

pocket watches . The ope rations are as follows : machining the middle to

take the pendant, brazing- on the pendant, cleaning the brazed spot and

sizing the middle and pendant, machining the hole and the projections for

the winding c rown and bow.

3 1 3

The axis of the hole ( 1 . 3 8+0. 04 mm diameter ) (Figure 42 ) must be parallel

to the plane of the fitting p rojection for the movement and at a distance of

1 . 1 0± 0 . 02 mm from it. The noncoincidence of the hole axis and the central

axis of the middle must not e xceed 0 . 0 5 mm.

FIGURE 4 0 . Blank of pocket-watch

middle

FIGURE 42 . Drilling 1 .38 mm diameter
hole

FIGURE 41 . Middle after roughing operation

FIGURE 43. Milling the crown recess

the pendant

The drilling and reaming of the hole are followed by milling of the re

cess for the winding crown in the pipe (Figure 4 3 ), using a hollow mill on

an S-2 vertical milling machine.

The

0 2 . 2

mm recess is then bored by a counterboring tool to a depth of

7 mm (Figure 44 ), and the burrs are removed from the pendant face and

the milled contour by a compound milling cutter.

The middle thus prepared is the n subjected to the finishing operations :

turning the fitting projections for the bezel and back, and machining the

inner recesses for the watch movement.

1174

3 14

The fitting projections for the bezel and back are turned on the S - 8 1A

s emiautomatic machine in two consecutive operations (Figure 4 5 ).

The internal fitting surfaces of 36

g�

and 3 5 . 8 5+0. 1 0 mm diameter are

also bored on the S - 8 1A s emiautomatic machine, the bezel-fitting projection

serving as a ;reference (Figure 46 ). The maximum permiss ible runout of

the bezel-fitting projection (4 1 . 2 m m ) relative to the movement-fitting bore

( 3 6 mm diamete r ) is 0 . 0 5 m m .

FIGURE

44 .

Facing and boring the crown hole

with a counterboring tool

The burrs in the winding- stem hole are removed manually after the

movement-fitting bore is completed . The middle is then chromium - plate d .

The bezel and the c a s e back o f pocket-watch cases are machined i n the

same manner as the corresponding wristwatch parts . The pendant bow is

manufactured from wire by coiling it on a mandrel in a close spiral and

cutting with a milling cutter .

FIGURE 4 5 . Turning the projections of

the middle

3 1 5

FIGURE 46 . Internally machin
ing the middle

GOLD AND GOLD-PLATED CASES

Well-polished cases made of gold or gold-plated nickel silve r have an

aesthetic appearance which is pres erved for a long time . Gold, as is well

known, is not tarnished by atmospheric air, and resis ts the co rrosive action
of water, bases and acids (aqua- regia e xcepted). Gold cases usually have

an attractive shape, especially those for ladies ' wristwatches where the

case shape blends harmoniously with the shape of the gold bracelet.

Cases are usually made of gold of 583 %o or 7 5 0 %o �' purity (meaning that

the alloy c ontains 5 8 3 or 7 5 0 parts of pure gold, the remainder being copper

and s ilver in various proportions ). More silver in the alloy imparts a bright

appearance, while increasing the p ropo rtion of copper gives it a reddish
shad e . Pure gold is very s oft and malleable , and the copper and s ilver are

added to it in order to give the gold alloy the necessary hardne s s . Fourteen

carat gold has a hardness of RB 8 7 to 9 0 and resists wear, this being very
important both for the cons ervation of the lustre and for the preservation

of the case weight.

The technology of gold- case manufacture is s imilar to that used in the

manufacture of nickel - silver cases with m odifications in the cutting condi

tion s . The most complex ope ration is the brazing of the case lugs . The

b razing alloy should be of the same carat number as the case, and brazing

should be carried out at a temperature near the melting point of gold. Local

heating is used to p revent the deformation of the part and the brazing is

performed in a protective medium to preserve the uniform color of the case .

The technical specifications for the manufacture of gold cases specify

that the gold chips must be collected after each operation. The machines

a re e quipped with special plexiglass shields and the washing and cooling

liquids are specially filtered.

Cases are polished on standard machines (of the S - 4 2 typ e ) by felt disks

charged with chromium - oxide paste .

In o rder to reduce the quantity of gold chips, the case is s o s haped that

it can be obtained by s waging.

Small- size ladies ' watch cases usually have such a shape and their weight

is between 3 and 8 g, while the weight of m en ' s wristwatch cases is between

1 1 and 2 0 g. Pocket- watch cases, with one or two backs , weigh between

25 and 40 g, and sometimes as much as 5 0 g.

The production of gold- plated cases in very large quantities has recently

begun abroad, the object being gold economy and price reduction. The base

used is nickel silver or special brass and the gold plating can be produced

by thermal, galvanic o r mechanical methods .

The thermal method is the m ost widely used, as it pro duces a strong

bond between the gold alloy and the base m etal . A 3 00 X 6 0 X 2 0 mm nickel

silver or special brass plate is sandwiched between two gold- alloy plates

of at least 1 4 - carat gold content and having dimensions of 3 00 X 6 0 X 3 and

3 0 0 X 6 0 X 1 . 5 mm, respectively. A special paste is applied between the plate s .

Steel plates o f 3 00 X 6 0 X 2 0 mm each are added and the entire stack i s com
pre- s ed by 4 to 5 clamps and placed in a gas furnace, where it is heated to

a predetermined temperature . The clamps are adjusted several times dur

ing the heating proces s , which lasts fo r 3 5 - 4 0 minutes . A s urface diffusion

of one metal into the other occurs during the heating and when the process
has been completed the ensuing bimetallic strip is rolled in s everal passes,

•

[Corresponds t o a purity o f 1 4 and

carat, respectively. ]

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Content .. 77 78 79 80 ..