Magnetically controlled torque wrench produces the required torque values accurately, and prevents overtorquing. The force between a magnet and a soft iron bar on the arms of the wrench constitutes a predetermined maximum torque that cannot be exceeded. So long as the magnetic flux remain constant, the torque remains the same

Rohrer, J. A.

English

NASA Technical Reports Server

June 1968	 Brief 68-10209 
AEC-NASA TECH BRIEF 
TES
AEC-NASA Tech Briefs describe innovations resulting from the research and development program 
of the U.S. AEC or from AEC-NASA interagency efforts. They are issued to encourage commercial 
application. Tech Briefs are published by NASA and may be purchased, at 15 cents each, from 
the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Magnetically Controlled Torque Wrench Prevents Overtorquing 
Drive Arm	 Handle Arm 
Soft Iron Bar 
Note: Permanent Magnet Type Only; Electromagnetic Type Not Shown 
The problem: 
To design a torque wrench that incorporates the 
repeatability of magnetic attraction, produces the 
required torque values accurately, and prevents over-
torquing. 
The solution: 
The force between a magnet and a soft iron bar on 
the arms of a torque wrench constitutes a prede-
termined maximum torque that cannot be exceeded. 
So long as the magnetic flux remains constant, the 
torque remains the same.
How it's done: 
The iron bar is attached to the drive arm of the 
wrench and the magnet to the handle arm. As soon as 
the torquing force exceeds the magnetic force, the 
contact faces separate and the hold is released. If an 
electromagnet is used, the torque force can be con-
trolled by the power supply. Since torque output is 
equal to the product of lever arm length and magnetic 
force, it is directly proportional to the input current to 
the electromagnet; therefore, a current scale, cali-
brated in units of torque, could be used for. accurate 
(continued overleaf) 
This document was prepared under the sponsorship of the Atomic 	 liability resulting from the use of the information contained in this 
Energy Commission and/or the National Aeronautics and Space document, or warrants that the use of any information, apparatus, 
Administration. Neither the United States Government nor any per-
	 method, or process disclosed in this document may not infringe pri-
son acting on behalf of the United States Government assumes any vately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19680000209 2020-03-12T05:35:18+00:00Z
control. The permanent magnet does not offer the 
control capabilities of the electromagnet, although the 
holding force can be changed by varying the position 
of the iron bar so that the contact area changes. The 
advantages of using a permanent magnet are portabil-
ity and simplicity in manufacture and use. 
Note: 
Inquiries concerning this innovation may be di-
rected to:
Sandia Office of Industrial Cooperation 
Org. 3413 
Sandia Corporation 
Post Office Box 5800 
Albuquerque, New Mexico 87115 
Reference: B68-10209
Patent status: 
No patent action is contemplated by AEC or 
NASA.
Source: John A. Rohrer 
(SAN-10002) 
Brief 68-10209	 Category 05


Magnetically controlled torque wrench prevents overtorquing

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