Content .. 38 39 40 41 ..

Technology of watch production - part 40

The indicator and the micrometer are mounted on the s ame bas e . The

micrometer s erves for establishing the nominal dimension (length or dia

meter ), and the indicator for measuring within the tolerance range . The

convenience of this instrument lies in the fact that dim ens ions from 0 to

1 0 mm can be m easured on it to a high degree of accuracy.

nom.

toler-

ina!

a nee

1 2-0.24

+0.01 3

16_0.24

+0.013

TABLE 26

Dimensions of slotting cutters, mm

nom·

toler-

ina!

a nee

0.1 0

+0.01

0.12

+O.OI

0.15

+0.015

0.18

-t

O.DI5

0.20 + 0.015

0.15

+0.015

0.18

+0.015

0.2(;

+ 0.02

0.25 + 0.02

0.30

+0.02

0.35

+0.02

0.40

+0.02

0.45

+0.02

0.50

+0.02

0.60

+0.02

•

56 0.1

64 0.1

For

b•aJ

Type

nom

toler-

ina!

a nee

20_0.28

+0.013

24-0.28

8 +0.016

30_0.28

+0.016

toler-

ina!

a nee

0.15

+0.015

0.20

+ 0.02 70 0.1

0.30 +0.02

0.40 +0.02

0.50

+0.02 64 0.2

0.60

+0.02

0.30

+0.02

0.1

0.40

+0.02

0.50

+0.02

0.60

+0.02

70 0.2

0.30

+0.02

0. 1

0.40 +0.02

0.50

+0.02

0.60

+0.02

FIGURE

34.

Horizontal micrometer with scale

divisions of 0.01 mm, and range of 0 to 15 mm

fiGURE 35. K-6 instrument with indicator scale
divisions of 0.001 mm, and micrometer scale di
visions of 0.01 mm

1 57

Internal diameters are measured by means of plug gages . A set of such

gages, with intervals of 0 . 002 5 mm between them, s erve for measuring

holes  with diameters  between  0 . 05  and  0 . 3  mm .  The  accuracy  of  these  gages
is ±  0. 0005 mm.  The  gage  ( 1 )  is  ins e rted in the bushing (2) and  is  s upported
in the handle  ( 3 )  (Figure  36 ) .

FIGURE

3 6 .

?lug gage :

FIGURE

37.

Set of gages

00 pieces)

gage; 2-bushing; 3- handle,

The gage diameter is written on the handle in hundredths of a milli-

meter (a gage o f 0 . 2 5 5 0 mm diameter i s designed 2 5 . 5 0 ). The gages are

arranged in s ets of 1 00 (Figure 3 7 ). The gages can s e rve as standards when
adjusting indicators and micrometers for relative meas urements .

Ring and plug thread gages are us ed for checking external and internal

threads , respectively.

The surface-finish quality of machined parts is determined, under plant

conditions , by m eans of a microscope with a magnification of 1 6X to 32X.

1 5 8

C h a p t e r V

MILLING THE TEETH OF GEA R WHEELS,

PINIONS, AND CLUTCHES

Toothed transmissions in pocket- and wris twatches transmit mom ent

from the mainspring to the balance and balance spring sys tem , rotation

from the es cape wheel to the hands , and force from the human hand to the

winding m echanism for periodically winding the mainspring.

The trans miss ion ratio between the barrel arbor and the escape wheel

can be as much as 1 : 5400, and the amount of energy s to red in the wound

mainspring is s mall . The moment transmitted to the escape wheel is there

fore very small : in the case of the "Zarya " brand of ladies ' wristwatches

the moment transmitted to the escape wheel is

Mmln

0 . 0 3 0 gmm .

The gear transmiss ions in watches must, therefore, have a high effi

ciency; that is , the friction los s es both between the m es hing teeth and in the

bearings must be at a minimum . In order to reduce the dimensions of

watches , gear modules of 0 . 0 7 - 0 . 3 0 mm and driven wheels (pinions ) hav

ing 6 - 1 2 teeth are us ed.

These basic requirements are the determining factors which lead to the

use in watches of a modified cycloidal gear-tooth form , which we will refer

to as "w a t c h g e a r i n g" .

T h e t o o t h c o n t o u r o f t h e w h e e l s a n d p i n i o n s o f w a t c h

m e c h a n i s m s can , however, have an epicycloidal , hyp ocycloidal or

involute form .

The epicycloid curve is generated by rolling a generating circle I on a

base circle II, the center of the generating circle lying outside the bas e

circle (Figure 1 , a ) . Any point

on the rolling circle des c ribes an epi

cycloidal arc

01A .

The hypocycloid curve is generated by rolling a generating circle II on

a base circle I , the center of the generating circle lying inside the bas e

circle (Figure 1 ,b ) . Any point

o n the rolling circle des c ribes a hypo

cycloidal arc

01A .

In the particular cas e , when the radius of the generating circle is equal

to half the radius of the bas e circle, the hypocycloid reduces to a straight
line directed along a bas e circle radius .

The involute curve is generated by rolling a s traight line on a bas e circle

(Figure l, , c ). The point

on the line describes an involute arc

01A .

In cycloidal gearing the tooth face is cons tituted by an epicycloidal arc,

and the tooth flank is a straight radial line (Figure 2 ) . In involute gearing
both the face and the flank are formed by a s ingle involute curve .

The difference between watch gearing and ordinary cycloidal gearing is

that in watch gearing the epicycloids are replaced by circular arcs . The

1 5 9

circular arc s elected is s imilar to the epicycloid (Figure 3 ) in the case of

gear wheel s , and differs considerably from it in pinions (Figure 4 ) .

The tooth tip form

is a s emicircle o f radius equal to half the tooth thick

nes s . The form

consists of circular arcs of radius equal to the tooth

thicknes s . Form

consis ts o f circular arcs o f radius equal to 2 / 3 the

tooth thickness . Form

is used relatively rarely and then for pinions with

more than 1 2 teeth. Form

is used for pinions with 6 or 7 teeth and is

called the o gival full - depth tooth form . Form

is widely us ed for pinions

with

> 7 and is called the o gival stub - tooth form .

FIGURE 1. Generating tooth forms :

a-epicycloidal; b-hypocycloidal; c-involute.

FIGURE

Cycloidal gearing

The reason for the replacement of the epicycloids by circular arcs in

gear-wheel teeth lies in the difficulty of producing milling cutters of epicy

cloidal contour.

1 6 0

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