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Shaft Design

On this site a shaft is specified as a cylindrical rod designed to transmit a power by rotation. It is specified to transmit torque

Indicative Transmittable Torque Values

This table is provided to allow comparison between shafts and is based on very simplistic assumptions with no allowance for fatigue, additional stresses to Bending Moments etc etc etc

Shaft Dia Pure Torque Power (100RPM)
mm Nm kW
30 132 1.4
40 313 3.3
50 612 6.4
60 1058 10.6
75 2068 21.6
80 2510 26
100 4900 51.3

Notes on table values

q = The skin torsion stress of a solid round shaft : T= The torque transmitted by the shaft : T = q.D3/5.1
The table is based on a torsion stress level of 25 N/mm2
Power transmitted by a shaft P = 2 * pi * T * N (N = Revs /sec)
Table power based on pure torque values

Methods of Locking/Driving items on Shafts

Type Description
KeyWay Reliable method based on a machined keyway in shaft and associated bore. Drive is via a fitted key. Results in increased local intensified stresses. A machined keyway results in a weaker shaft.(shaft dia. effectively reduced by 25%). Key can be deformed over time and result is a loose drive
Pin Very low cost option. Used for low torque drives.
Spline Expensive to manufacture with matching spline in shaft and bore. No additional components required. Allow relative axial movement. High torque capacity.
TaperLock Bush A Tapered Bush that fits into a tapered bore in the Gear/Coupling to be driven by the shaft. The locking action results from forcing the bush into the bore using axial screws. Tendency to stick in position. Limited shaft range (up to 80mm dia)
Shaft Locking Lock Bush Similar principles to taperlock bush but has parallel bore and OD. More convenient to install. Much larger size range (up to 500mm dia). These are relatively expensive but required no special shaft machining.
Interference Fit Requires accurate shaft and bore. Machined items are assembled using hydraulic press or using thermal methods e.g. Heating the female item or freezing the male item. Difficult to separate
Adhesive Low Cost. High torques can be transmitted. No special machining of shaft or bore. Cannot easily be taken apart. Should not be used without extensive development/testing
Hydraulic Locking Bush Similar application to locking bush. Large size range. Convenient to apply. No risk of sticking. Relatively expensive.

    Links to Information on designing shaft suppliers and shaft locking methods

  1. Staffs ..Audio Lecture Drive shafts an components
  2. Machine Design ..University Of Tennessee at Martin lecture Notes: Lots of useful information on pdf files
  3. Fenner Drives ..Information On Trantorque
  4. Lenze ..Supplier of Taperlock Bushes, Shaft Bushes, Hydraulic Locking Bushes
  5. OnSmartclickcom ..A treasure trove of notes on design of machine elements including shaft and gearbox design
  6. DANotes ..Very informative ..Section on Stress Strength and Safety for shafts

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Send Comments to RoyBeardmore@ic24.net

Last Updated 04/10/2003