6.4 Tooth-bearings Technicaldata Kgstockgears 44172k

6.4 Tooth bearings Regardless of how accurate the gear itself may be, poor tooth bearing not only causes oscillation and noise but also have bad effect on gear’s life span. Refer to Fig. 2. Extracted Tooth bearing on gear from JIS B 1741-1977 (old) JIS B1741 (old)「Tooth bearing on Gear」stipulates percentage of tooth bearing mark as follows. As for Tooth trace direction, it is percentage (%) of mean value bc of Length of tooth bearing for Effective length of trace - b’. As for Tooth depth direction, it is percentage (%) of mean value lc of tooth bearing width for Working depth- h’. Note∗ For edge of gear tooth with chamfering, Effective length of trace is after deducting chamfered area. For different Effective lengths of Tooth trace between Pinion and Gear, take the shorter side. Tooth bearing percentage of Tooth trace direction =

bc × 100(%) b'

(a) Cylindrical gear Spur gear

Tooth bearing percentage for Tooth depth =

lc × 100(%) h'

(b) Straight bevel gear Spiral bevel gear b' bc

b'

bc

lc

lc

h'

h'

Helical gear b'

(c) Cylindrical worm gear pair Worm wheel

bc

b'

lc

h'

bc

lc

h'

Fig. 2 Tooth bearing Refer to Fig. 3 for Bevel gear with Crowning and empty load. It is desireable that centre of tooth bearing in Tooth trace direction is about 60% of Length of tooth trace from heel.

100

60

Heel

Toe Fig. 3 Tooth bearing for Bevel gear with Crowning.

96

Percentage of tooth bearing for Worm gear pair is for Worm wheel engaged with Worm gear. In general, Tooth bearing to inflow side of flank of Worm wheel is not desirable. It is desirable for Tooth bearing centre in Tooth trace direction to be biased towards outflow side to make clearance at inflow side. (Refer to Fig. 4)

Fig. 7 Engagement for Bevel gear with Crowning {Gleason Company, INSTALLATION OF BEVEL GEARS (1965)} Coniflex® Bevel Gear (Straight bevel gear with Crowning) Ⓡ mark is Gleason Works trademark

Fig. 4 Tooth bearing for Worm wheel Revolving direction for Worm gear

(a)

Inflow side

Spiral bevel gear

(b)

Outflow side

Fig. 5 Inflow clearance for Worm gear pair ｛A few problems of lubricating oil for Worm gear pair and research work for machine. Volume 8, No. 4 (1956) written by Dr. Waguri and Dr. Ueno from Yokendo Co. Ltd.｝

(a) (b) Fig. (a) shows proper assembly method, (b) is assembled off centre from location of Top cone. Please observe the difference in position for Tooth bearing. Fig.8 Ideal tooth bearing for Bevel gear

Inflow clearance

Upper side

Worm gear

Lower side

Fig. 6 Line of for Worm gear pair (2 number of threads) and Tooth bearing for standard Worm gear. Quoted literature is the same as Fig. 5.

Re dir vo ec

ing lv ion t

360° 270° 90°

Lower side

Spiral bevel gear (Pinion: Shape of teeth is left hand)

270°

Start

Upper side

180°

0°

End

180°

360°

Upper side

of

co n

tact

90°

Lower side Upper side

Lower side

97

Table 4. P ercentage of tooth bearing for Cylindrical gear (Spur and Helical gears) Class

Percentage of tooth bearing Tooth trace direction

Tooth depth direction

Class

Percentage of tooth bearing Tooth trace direction

Tooth depth direction

A

Above 70% of Effective length Above 40% of Effective length of Tooth trace of Tooth profile

A

Above 50% of Effective length Above 40% of Effective length of Tooth trace of Tooth profile

B

Above 50% of Effective length Above 30% of Effective length of Tooth trace of Tooth profile

B

Above 35% of Effective length Above 30% of Effective length of Tooth trace of Tooth profile

C

Above 35% of Effective length Above 20% of Effective length of Tooth trace of Tooth profile

C

Above 20% of Effective length Above 20% of Effective length of Tooth trace of Tooth profile

Table 6. Percentage of tooth bearing for Bevel gear Class A B C

98

Table 5. P ercentage of tooth bearing for Worm gear pair (Worm wheel)

Percentage of tooth bearing Tooth trace direction

Tooth depth direction

Above 50% of effective length Above 40% of Effective length of Tooth trace of Tooth profile Above 35% of Effective length Above 30% of Effective length of Tooth trace of Tooth profile Above 25% of Effective length Above 20% of Effective length of Tooth trace of Tooth profile

Table 7. T able for Tooth bearing classification and System of accuracy Class

System of accuracy for Cylindrical gear

System of accuracy class for Bevel gear

JIS B 1702-1960 (old)

JIS B 1704-1973

A

1, 2

1, 2

B

3, 4

3, 4

C

5, 6

5, 6