Content .. 81 82 83 84 ..

Technology of watch production - part 83

motion is imparted to the funnel body by an eccentric shaft driven by pul

ley (5 ), and by the spring of the supporting center (6 ) placed inside the

head (7 ). The machine head ( 7 ) and the connecting arm ( 3 ) are fastened to
the machine bed.

Pulley (5) revolves at 145 rpm . A block is filled in 0 . 5 to 2 minute s .

A fter the machine has stopped the funnel body i s drawn back t o the left,

released from pin (4 ), rotated 90°, and the block removed. The holes which

remain empty are filled with screws manually.

Shellac or rosin is then poured onto the block. The block is first heated

on an electric heating plate till the shellac (or rosin ) melts , and then the

s crews are pressed against the block by means of a press . A fter the blocks

cool down, they are mounted on the S - 1 5 machine . Fastening by means of

shellac or rosin causes no deformation of the parts .

Tin+ antimony

!}Jf6

Cast iron

FIGURE 5. Polishing disk used in the S-15 machine

The blocks are mounted on the round table of the S - 1 5 machine and are

pressed down by weights placed on the upper ends of the spindles . A driver

bar with two pins is fastened to the lower end of each spindle . The conical

extremities of the pins fit the central holes of the blocks and press them

against the table . The blocks are automatically positioned relative t o the

table plane .

The S - 1 5 machine uses a finish-faced cast- iron disk of hardness 1 2 0 to

1 5 0 HB for lapping. A layer of abrasive paste is applied to the lap (see

Table 2 ).

A disk made of a 9 9 o/o tin 1

o/o

antimony alloy is used for polishing (Figure 5 ).

A layer of chromium oxide or diamantine':' paste is applied to the disk.

Wooden polishing disks made of beech o r lime are also used. Their flat

ness , however, quickly deteriorate s , the block is pres sed into the wood,

and as a result the polished parts have burrs at the edges .

• [See Tab!e 2 , Sect. 3 . ]

3 2 9

The weights on the upper end of the spindle transmit the required p re s

sure t o the block during lapping. One weight i s sufficient in polishing, and

it can even be dispensed with since the weight of the spindle and driver bar
is often sufficient.

Two separate machines , at a distance of 1 to 1 . 5 m from each other, are

used for the lapping and polishing operations in order to prevent abrasive

grains from falling on the polishing disk. The blocks mus t be carefully

cleaned of abrasives and washed in gasoline after lapping. Polishing is as

a rule performed in two operations (preliminary and final ). The lapping
and polishing paste s , and the materials used for fastening the parts to the

blocks , are selected in accordance with the configuration of the parts (see

Table 3 ).

Shellac ensures a stronge r bond between the parts and the block than

does rosin and it is therefore used for pressures of 2 . 0 kg

mm2 and above.

TABLE 2

Lapping and polishing pastes (compounds)

Paste characteristics

1 . Emery paste (for lapping)

Emery, %

. . . . . . . • . . . . . . • . . . . . . . • . . .

Grain size (grit),

. . • . • . . • . . • . . . . . . . . . .

Stearin,

o/a

. . . . . . . . . . . . . . . . . . . . . . . .

Lard,

"/o

. . . • • • • . . . . • • . • . • . . • • • • . • • • .

Kerosene, "/o

• • . . . • . • . • . • • . . . . . • . . . • . .

Surf ace-finish class

•

. . . •

•

. . . . • .

2. Chromium-oxide paste (for polishing)

Chromium-oxide,

"/o

. • . . . . • • . • . . . . . . • . •

Grain size (grit),

. . . . . . . • . • . . . • . . . . • . .

Stearin,

u/o

. . . . . . . . . . . . . . . . . . . . . . . .

Paraffin, %

. . . . . . . . . • . . . .

• · •

· · • ·

Oleic acid, %

• . . . . . . . • . . • . . . . . . . . . • . .

Graphite ,

"/o

• • • . . . • . . • . • • . . . • • . . • . • • •

Lard, %

•

• · · • · •

M-28

8- 9

M-3.5

0.2

Industrial fats, "/o

• • . • • • • • • . . . • . • • . . . • . •

1 .8

Kerosene,

"/o

. . • . . . . . . . . . . . . . • . . . • . . . .

Surface-finish class

. . . • . . . . . . . . . . . . . . . . .

11-12

3. Diamantine paste (for polishing)

Diamantine ( leuco-sapphire or monocorundum),

"/o .

Grain size (grit),

fl . . . . . . . . . . . . . . . . . . . .

Beeswax

. • . . . . . . . • . . . . . • . . . • . • • . . . . .

Surface-finish class

. . • . . . . . . . . . • . . . . . . . •

Paste type

M-20

2.5
2.5

9-1 0

6 0

M-3.5

12-1 3

M-3.5

1 3

M- 3 .5

13-14

Lapping and polishing conditions. During the operation of the machine ,

when the table and spindles revolve s imultaneously, the block carrying the

parts performs complex motions relative to the lap , as a result of which a

uniform laye r of metal is removed from parts both near and far from the

block cente r. The lapping speed varies between 0 and 3 m

sec .

The same process conditions are used for lapping and polishing parts

made of different grades of steel . The machining (basic ) tim e depends on

the area of the parts to be machined and on the allowance . In practice , the

3 3 0

machining time is calculated on the basis of standards established in the

watch plant s . A table for calculating the lapping time for steel parts with

0 . 02 mm allowance is given in Appendix 6 . The auxiliary time is als o deter

mined on the basis of standards .

TABLE 3

Lapping and polishing pastes (compounds)

Pressure, k

mm2

Material used for

Types of parts

lapping

polishing

fastening the parts

Lapping pastes

Polishing pastes

to the block

Scre\YS, ratchets,

1-2

0-5

Rosin

Emery paste-

Chromium-oxide

regulators, caps,

type A

paste- type B

etc.

Escape wheels,

2- 3

0-5

Shellac

Emery paste -

Chromium-oxide

pallet levers,

type B

paste-type B

etc .

An allowance between 0 . 0 5 and 0 . 2 0 mm is fixed for (flat) surface lapping,

and the allowance for preliminary and final polishing is between 0 . 0 1 and

0 . 02 mm.

The deviations in the dimensions of parts polished on the S- 1 5 machine

do not e xceed 0 . 0 1 to 0 . 02 mm, and therefore, in certain cases no particular

allowance is established for polishing and the decrease in dimensions is at

the expense of the final - dimension tolerance .

The operation o f the S - 1 5 machine i s s tarted by turning the handle ( 2 3 )

(see Figure 2 ). This lowers the spindles so that the ends o f the driver-bar

pins penetrate into the conical recesses in the work blocks and press the

blocks against the table . The electric m otor is then s witched on, and the

spindles and table begin to rotate . Paste is applied periodically by hand .

A fter the lapping, the spindles are lifted, the blocks are removed,

cleaned of abrasive s , and the height of the parts is measured by means of

a dial gage. If the dimension is larger than specified, the blocks are again

loaded into the machine, and the parts ar� lapped again.

Surface-finish quality after lapping and polishing is inspected visually

using a magnifying glass ( 5X). A microscope ( 1 6X) is used in some cases .

A fter the polishing, the block with the finished parts is dismantled.

Polishing P inion Teeth

A fter milling, pinion teeth have a class 8 or 9 surface-finish quality which

is raised to class 1 1 or 1 2 by polishing.

The pinion teeth, which have a hardnes s of 52 to 5 5 HRc after hardening,

are polished on the S- 5 (Figure 6 ) or the S- 83 machine with type A chromium

oxide applied to the beech disk on the machine .

The polishing disk ( 1 ) of the S - 5 machine i s m ounted on the spindle ( 2 )

o f the rocker arm ( 3 ). The pinion i s freely placed o n its journals o r pro

j ections in the steady- rest (4 ), which is held between centers on the heads ( 5 )

mounted o n slide ( 6 ) .

3 3 1

The polishing disk has a spiral flute along its circumference . When the

rocker arm is lowered, the flute meshes with the pinion teeth and the pinion

rotates about its axis as the disk rotates . If the length of the teeth is more

than 2 mm, a reciprocating motion is imparted to slide (6 ) by the connecting

rod ( 7 ) and the crank ( 8 ) . A belt is slipped over pulleys ( 9 ) and ( 1 0 ) to pro

vide power for the reciprocating motion .

The inserts for the steady- rest are made of carbide and are brazed to

the rest with copper

(

Figure 7 ) .

The beech polishing disk wears rapidly. The flutes i n the disk are cut

directly on the machine and, for this purpose, the slide with table is rotated

by 5 to 6 ° . The disks are made o f a single piece of wood without knots or

any other flaws. Disks made of an 87 o/o lead, 4 o/o tin and 9 o/o antimony alloy
are more wear-resistant, and in addition give a better - quality polish.

Technical data, S-5 machine

Polishing rate, m/sec . . . . . . . . . . . . . . . . . . .

4- 7

Maximum pinion diameter, mm . . . . . . . . . . . .

Maximum module, mm

•

. . . . . . . . . . •

. . •

Polishing-disk diameter, mm

. . • . . . •

•

• •

7Q- 150

Polishing-disk spindle speed, rpm .

. . . • • . . . •

750

Number of strokes of part slide per minute .

• • •

•

113

Maximum spindle travel, mm

• . . . • • • • • • •

. .

FIGURE 6 . S-5 pinion-tooth polishing machine

3 3 2

Content .. 81 82 83 84 ..