KEYS
Definitions:
1. Key – a machine member employed at the
interface of a pair mating male and female circular
cross-sectional members to prevent relative angular
motion between these mating members.
2. Keyway – a groove in the shaft and mating
member to which the key fits.
3. Splines – permanent keys made integral with the
shaft and fitting into keyways broached into the
mating.
4. Square key – has a square cross section with half
of its depth sunk in the shaft and half in the hub.
Definitions:
5. Flat key – has a regular cross section with a
smaller dimension placed in the radial direction
with half sunk in the shaft and half in the hub and
is used where the weakening of the shaft by the
keyway is serious.
6. Round key – has circular cross section.
7. Barth key – is a square key with bottom two
corners beveled.
8. Woodruff key – consists of one-half of a
circular disk fitting into a rectangular keyway in
the female member and a semi-circular keyway in
the male member.
9. Gib-head taper key – is a flat key with a
special gib-head to facilitate easy driving and
removal of the key.
10. Saddle key – is a flat key used without a
keyway in the shaft.
11. Kennedys key – are tapered square keys with
the diagonal dimension in a circumferential
direction.
12. Feather key – is one which has a tight fit into
one member and a loose sliding fit in the mating
member thus allowing the hub to move along the
shaft but prevents rotation in the shaft.
Formulas
1. Power of key:
A. P = 2πTN, KW
2πTN
B. P = , Hp
𝟑𝟑,𝟎𝟎𝟎
2. Force transmitted, F
𝐓 𝐓
F= =
𝐫 𝐝/𝟐
Where:
d = shaft diameter
3. Compressive Stress of key
Fc
Sc = 𝐡
𝐋
𝟐
4. Shearing Stress of key
Fs
Ss =
𝐰𝐋
Where:
L = length of key
w = width of key
h = height of key
5. Relation of key and shaft for the same
material:
w = D/4 L = 1.2D
6. Force tangent to pulley rim
T = T’
F . r = F’ . R
Where:
F = force tangent to the key
F’ = force tangent to pulley rim
R = radius of pulley
