T-56
6.10.4 Helical Rack
Viewed in the normal direction, the meshing of a helical rack and gear is the same as a
spur gear and rack. Table 6-6 presents the calculation examples for a mated helical rack with
normal module and normal pressure angle standard values. Similarily, Table 6-7 presents
examples for a helical rack in the radial system (i.e., perpendicular to gear axis).
Radial Module
Radial Pressure Angle
Helix Angle
Number of Teeth & Helical Hand
Radial Coefficient of Profile Shift
Pitch Line Height
Mounting Distance
Pitch Diameter
Base Diameter
Addendum
Whole Depth
Outside Diameter
Root Diameter
mt
at
b
z
xt
H
ax
d
db
ha
h
da
df
2.5
20°
10° 57' 49"
20 (R) – (L)
0 –
– 27.5
52.500
50.000
–
46.98463
2.500 2.500
5.625
55.000
–
43.750
Item
Symbol
Formula
No.
zmt
––––– + H
+ xt mt
2
zmt
d cosat
mt (1 + xt)
2.25mt
d + 2 ha
da – 2 h
1
2
3
4
5
6
7
8
9
10
11
12
13
Rack
Gear
Example
Table 6-7 The Calculation of a Helical Rack in the Radial System
Normal Module
Normal Pressure Angle
Helix Angle
Number of Teeth & Helical Hand
Normal Coefficient of Profile Shift
Pitch Line Height
Radial Pressure Angle
Mounting Distance
Pitch Diameter
Base Diameter
Addendum
Whole Depth
Outside Diameter
Root Diameter
mn
an
b
z
xn
H
at
ax
d
db
ha
h
da
df
2.5
20°
10° 57' 49"
20 (R) – (L)
0 –
– 27.5
20.34160°
52.965
50.92956
–
47.75343
2.500 2.500
5.625
55.929
44.679
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Item
Symbol
Formula
No.
tanan
tan–1(––––––)
cosb
zmn
–––––– + H
+ xnmn
2cosb
zmn
–––––
cosb
d cosat
mn (1 + xn )
2.25mn
d + 2 ha
da – 2 h
–
Rack
Gear
Example
Table 6-6 The Calculation of a Helical Rack in the Normal System
