MACHINE TOOL DESIGN - MECHANICAL
TOPIC : DESIGN OF KEYS
By:
HV RajaShekara
SENIOR DIRECTOR - Design Institute,
IMTMA
Keys
• A key is define the piece inserted in a axial
direction between a shaft and hub to prevent
relative rotation but allow sliding movement
along the shaft if required.
• Keys are temporary fastening and are always
made of mild steel because they are subjected
to shearing and compressive stresses caused by
the torque they transmit.
• a keyway is the groove cut in the shaft or hub to
accommodate a key. Key ways can be milled
horizontally or vertically .
Keyways milled
Classification of keys
• Saddle keys
• Hollow saddle key
• Flat saddle key
• Sunk keys
• Taper sunk keys
• Parallel sunk keys
• Father keys
• Woodruff key (adjustable key)
• Round keys
• Parallel pin
• Taper pin
Saddle keys
• Saddle key are taper keys which are
sunk into the hub only.(note: a taper
key in uniform in width but tapered in
thickness on one side, usually 1:100
and is used where no axial movement
along the shaft is required).
• Saddle key is suitable for light duty,
since they rely on a friction drive alone
and are liable to slip on the shaft under
load.
Type of the saddle key
• Hollow saddle key:
• this key has its underside hollow out so that it can be
placed on the curved surface of the shaft. The keyway is cut
in the mating piece (hub) only. Hollow saddle key is used
for light duty.
• Flat saddle key:
• In this the flat surface is made on the shaft over which the
key is placed in position . In this , holding force is
comparative large than the hollow saddle key. It is used for
light duty.
• Let D = dimeter of the shaft
• Width of the key, W = D/4
• Nominal thickness at the large end , T = W/3 = D/12
• Length of the key , L = D to 1.5D
• Taper on the top surface = 1:100
Sunk keys
• Sunk keys are sunk into the shaft and into the hub.
These keys are suitable for heavy duty since they rely on
positive drive.
• Taper sunk keys:
• This is the standard form of the key and may be either of rectangular or square
cross-section .the key is sunk in the shaft to a depth of half its nominal
thickness when measured at the side.
• This key gives a very sound fastening without any fear of slipping between the two
parts, unless , of course, the key shears. Such a key can be safely used for heavy
duty work.
• Rectangular cross-section
let D = diameter of the shaft
width of the key W = D/4
nominal thickness T = (2/3)W = (1/6)D
• Square cross-section:
T=W
Parallel sunk key
It is uniform in width
and thickness
throughout. It is thus
taper less and is used
where the pulley or
other mating piece is
required to slide
along the shaft. It
may be rectangular or
square cross-section
and their ends may be
squared or rounded.
Woodruff keys
It is an adjustable sunk key. It
is in the form of a semi-
circular disc of uniform
thickness. The key fits into a
semi-circular keyway in the
shaft and the top of the key
fits into a plain rectangular
key way in the hub of the
wheel. Since the key and the
key seat bear the same
radius , it has the advantage
of adjusting itself to any
taper of the slot of the hub
or boss of wheel.
KEYS NOMEMCLATURE
KEYS NOMEMCLATURE
KEYS BEARING PRESSURE
ALLOWABLE BEARING PRESSURE
BEARING PRESSURE CALCULATION
BEARING PRESSURE CALCULATION
FOR SLIDING
KEYS
BEARING PRESSURE CALCULATION
BEARING PRESSURE CALCULATION
BEARING PRESSURE CALCULATION
WOOD RUFF KEY
Spline shaft and hub
• A spline shaft is used when the hub is required to slide
along the shaft. These shafts are used mostly for sliding gear
application as in automotive gear box and propeller shaft of
aircraft.
• A spline shaft in which are cut equiangular longitudinal
groove, the metal between these groove forming splines or
feathers of uniform depth.
• By this means the power transmitted is equally divided amongst the
number of keys giving great strength and security against total failure than
by using a single key.
Spline shaft
SPLINES STANDARDS
SPLINES STANDARDS
SPLINES STANDARDS
Calculations for checking bearing Pressure of Keys
Sl.No. Symbol Item Value Units Remarks
1 Type of Key Parallel Key for Machine Tools with rounded ends
2 d Shaft diameter 30 mm
3 b Width of key 8 mm Table 8 P178 MTDHB
4 h Height of key 7 mm Table 8 P178 MTDHB
5 l Length of key 40 mm Table 8 P178 MTDHB
6 t2 Depth of key in the hub 1.7 mm Table 8 P177 MTDHB
7 t1 Depth of key in the shaft 5.3 mm Table 8 P177 MTDHB
8 Kw Power Transmitted 3.7 Kw
9 n Speed of shaft 1440 rpm
10 T Torque transmitted at n rpm (975xKwx1000/n) Kgf mm
2505.208333 Kgf mm
11 F Tangential Force 2T/ d Kgf
167.0138889 Kgf
12 A Bearing Area of Key t2 ( l - b) mm
54.4 mm sq
13 P Bearing Pressure P= (F / A) Kgf / mm sq
3.070108252 Kgf / mm sq
14 Pmax Max. Permissible bearing pressure 8 to 10 Kgf / mm sq For unhardened Steel Keys
10 to 12 Kgf / mm sq For hardened Steel Keys
Calculation of Splines
Sl.No. Symbol Item Unit value Remarks
1 D Major Diameter of Spline mm 28 T10 p180
2 d Minor Diameter of Spline mm 23 T10 p180
3 n No. of Splines No. 4 T10 p180
4 c Chamfer of edges in hub mm 0.3 T10 p180
and Spline
5 l Length of the hub mm 46
6 Kw Power Transmitted Kw 7.5
7 N Shaft Speed rpm 1000
8 h' Height of one contact mm [(D - d)/2c -2c]
Surface 7.733333333
9 n' No. of effective contact No. (2/3 to 3/4)n
surfaces 2.666666667
10 h Total height of effective mm n'h'
contact surfaces between 20.62222222
shaft and hub
11 T Torque transmitted Kgf.mm 975xKwx1000/N
7312.5
12 F Tangential Force Kgf 4T/(D+d)
573.5294118
13 P Bearing pressure on Kgf/mm sq. F/h.l
contact surfaces 0.604592005
14 P Per Permissible bearing Kgf/mm sq. Table 7 P174
pressure in splines and
spline shafts
Table 7, P 174 Permissible values of bearing pressures
In Splines and Spline shafts
Sl.No. Type of Working conditions Unhardened Hardened
Connection Flanks Flanks
1 Heavy (Shocks in
both directions, vibrations, 1.5 - 2 2 - 3.5
Sliding insufficient lubrication,
without less accurate manufacture)
load Medium 2 -- 3 3 -- 6
Good 2.5 -- 4 4 -- 7
2 Sliding Heavy ----- 0.3 -- 1
with Medium ----- 0.5 -- 1.5
load Good ----- 1 -- 2
Heavy 3.5 -- 5 4 -- 7
3 Stationary Medium 6 -- 11 10 --14
Good 8 -- 12 12 -- 20
THANK YOU
