07 shaft diameter
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Shaft Design: Diameter
determination
Design 1
Mechanical Engineering FacultyEngineering Division
Universidad Santo Tomás
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What is a shaft ?
It is a rotating machine element thattransmits power or motion.
It is usually a slender element of roundcross section (hollow or solid).
It usually carries power-transmittingcomponents (gears, belt sheaves, chainsprockets)
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What is a shaft ?
Keys, pins, snap rings, clamp collars, shoulders,interference fits, are used to secure power-transmitting components.
A shaft is usually supported by bearings (rolling-contact or journal).
Most shafts are under fluctuating loads of combined bending and torsion with variousdegrees of stress concentrations.
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Common shaft topologies
Constant
Diameter
Stepped
Crankshaft
From Convertech Website
From HUP YIK Website
From Tianrun Website
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Stepped Shaft example
From Norton, p. 506.
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Others Shaft examples
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Other definitions
Axle: nonrotating element that carries no torque
and it is used to support rotating members
(pulleys, wheels). It is a “round beam”
Spindle: short shaft.
Flexible shaft : transmits motion between two
points where the rotational axes are at an angle
with respect to one another.
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Other Definitions
AxleSpindle
Flexible Shaft
From Melrose Wheel Chairs Website
From 4WD Factory Website
From Flexishaft Website
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Materials for Shafts
Steels
Cold-drawn or machined from hot-rolled, plain carbon steels
Alloy steels
Carburizing grade steels
Stainless steels
Nodular High Strength Cast Iron
Bronze
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Shaft Design process
1. Design based on strength
2. Deflection Verification (stiffness design)
3. Critical Speed Verification
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1. Design based on Strength
1.1 Determine rotational speed and power to be
transmitted by the shaft.
1.2 Determine the power-transmitting
components that will be mounted on the shaft.
1.3 Specify the location of bearings.
1.4 Propose the general topology of the shaft,
considering the attachment method for each
power-transmitting component.
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1. Design based on Strength
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1.5 Produce a complete static analysis of theshaft (free-body diagram, determination of the
radial and axial forces exerted on the shaft,
Solving for the reactions on all bearings).
1. Design based on Strength
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1.6 Produce the complete torque, shearing force
and bending moment diagrams to determine the
distribution of bending moments and torque inthe shaft.
Once you finish these six steps, you can identify
critical locations on the shaft, i.e., sections withhigh torsion-bending magnitudes and presence
of notches.
1. Design based on Strength
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1.7 Select the material and specify its condition.
1.8 Choose the appropriate minimum acceptable
diameter equation, according to the type of loading.
1.9 Determine the minimum acceptable diameter
for each critical location.
1.10 Specify diameters for each step, considering
tolerances and fits, preferred sizes, mounting
parts, etc. ITERATIVE PROCESS
1. Design based on Strength
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ASME Design Equation
SAFE
ZONE
N f > 1
FAILURE
ZONE
N f < 1
3
32
d
M K a
f a
3
16
d
T mm
Fully reversed bending:
Steady torsion:
von Mises relationship:3
y
ys
S S
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General Equation (Goodman
Criterion)3
32
d
M K a
f a
Fluctuating bending:
Fluctuating torsion:
3
32
d
M K m
fmm
3
16
d
T
K m
fsmm
3
16
d
T
K m
fsa
von Mises Stresses: 2/122'3 aaa 2/122'
3 mmm
f ut
m
f
a
N S S
1''
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Preliminary K t values
Bending Torsion Axial
Shoulder-sharp fillet 2.7 2.2 3.0
Shoulder – Well rounded fillet 1.7 1.5 1.9
End Mill Keyseat 2.2 3.0 -
Sled runner keyseat 1.7 - -
Retaining ring groove 5.0 3.0 5.0
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Preliminary K t values
Shoulders:
Well rounded filletSharp fillet
Adapted from Mott, p.542.
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Preliminary K t values
Keyseats:
Adapted from Norton, p.528-529.
End-Mill (profile) Sled runner
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Preliminary K t values
Keyseats:
Adapted from Norton, p.529.
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Preliminary K t values
Retaining Ring Grooves:
from Seeger-Orbis website.
Tipical radius at the bottom of the groove: 10% of the ring thickness ≈ m/10
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References
Norton, R.L. Machine Design: an integratedapproach. 3rd ed, 2006.
Budynas and Nisbett. Shigley’s MechanicalEngineering Design. 8th ed, 2006.
Mott, R.L. Machine Elements in MechanicalDesign. 4th ed, 2004.
Deutschman et al. Diseño de Máquinas. 1987.
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References
Convertech Website
http://www.convertech.com/small-diameter-
expanding-air-shafts.php
HUP YIK Website
http://hupyik.com/products/productList.aspx?cate
gory=Water%20Pump%20Part&pageIndex=1
Tianrun Crankshaft Co Website.
http://tianrun.en.gasgoo.com/auto-
products/17399.html
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References
Melrose Wheel Chairs Website
http://www.melrosewheelchairs.com/index.php?m
ain_page=product_info&cPath=8_4&products_id
=124
4WD Factory Website
https://www.4wdfactory.com/store/products.php?
product=Dana-44%2C-GM-10-bolt-Front-
Spindle%2C-6-Hole-Flange%2C-Big-Bearing-
Journals
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References
Flexishaft Website.
http://www.flexishaft.com/powertransmission.htm
Seeger-Orbis Website
http://www.seeger-orbis.com/en/design-details