16 
The N.Z. Journal of Science and Technology. 
[Feb. 
DESIGN OF LAMINATED SPRINGS. 
By S. H. Jenkinson. 
The theory of the design of laminated, or plate, springs is, if we are to judge 
by contemporary 'text-book and technical-magazine literature, in a very 
incomplete state, and the practice is full of manifest errors. The author 
first fully realized the existing confusion in 1907, when he attempted to 
check the design of a particular spring by the application of eight formulae 
given by the best-known authorities. The number of leaves required to sup¬ 
port the load as ascertained from these standard formulae varied as follows: 
9, 10-7, 11*5, 12, 12*2, 13*3, 13-7, 15 ! All these formulae derived from what 
is generally known as the “ theoretic ” spring, so the first step obviously lay 
in a fuller consideration of the basic principles. The first step forward came 
with an unsigned article* in The Engineer , which specified certain definite 
overhangs and corresponding stresses for each leaf. Here was evidently 
some entirely new conception underlying the design of laminated springs ; 
and, working back from the conclusions given, it was discovered that the 
writer had assumed that each leaf carried the full load at the point only, 
and with this “ Open Sesame ” the problem quickly solved itself. In the 
article certain mistakes were made, the deflection due to shear had been 
entirely overlooked, and the possibility of obtaining equal stresses in each 
leaf was not recognized ; nevertheless, here for the first time appeared work 
based on what is now obvious as the fundamental assumption of laminated- 
spring design. 
In 1909 the author designed springs (see fig. 1) in accordance with the 
complete formulae which are published in this article (for the first time, 
as the author believes), and during the last ten years the correctness of the 
design has been abundantly tested in actual practice in railway working. 
* Design of Plate Springs, The Engineer (London), vol. 93, p. 157, 14th February, 
1902. 
