Low Cost Automation Tutorial

#94 Motion mechanism design - 39: Shaft-boss fastening methods

Category : Drive mechanism design

October14, 2011

There are various shaft fastening methods available, including ones used to couple two shafts or to fasten a shaft to a boss for power or torque transmission. This section provides a brief comparative summary of shaft-boss fastening methods for power or torque transmission.

(1) Shaft-boss fastening methods

A mechanical element fastened to a shaft is called a boss. Typical shaft and boss fastening methods are shown below:

-Fastening with keys (See Fig. 1.)

[Fig. 1] Fastening with keys

-Fastening with setscrews (See Fig. 2.)

[Fig. 2] Fastening with setscrews

-Coupling with pins (See Fig. 3.)

[Fig. 3] Fastening with pins

-Frictional locking (See Sections 92 and 93.)

-Weld-fastening

(2) Comparison of fastening methods

Shaft-boss fastening method	Principle and features	Torque transmission capacity
Fastening with keys <Types> Flat key Saddle key Sunk key Round key	Keys (that may be shaped rectangular, round, conical, etc.) inserted into keyways in the shaft and boss to fasten them. JIS and DIN standardized Available in various shapes and highly reliable.	Flat key: Moderate Saddle key: Low Sunk key: High Round key: Low
Fastening with setscrews	Setscrews inserted through a boss to fasten the shaft. Poor compatibility with overload torque.	Low Used to secure a small (low-power) motor output shaft to a coupling.
Fastening with pins	Pins inserted into thru holes in the shaft and boss to couple them together. Suitable for coupling linkage mechanisms.	Low
Frictional locking	Clamping screws apply radial force to the shaft and boss to frictionally fasten them. User-friendly, allowing removal and reattachment and easy shaft alignment.	Low to high Torque transmission capacity variable depending on frictional force available from Mecha-lock selected.
Weld-fastening	Shaft and boss welded and firmly fastened together. Inconvenient because disassembly impossible after welding. Accuracy variations unavoidable due to weld strain, etc.	Moderate to high

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