04-04-2015, 11:25 AM #1
Calculating the Size of a Mainspring
LABOUNTY'S MAINSPRING FORMULA
The formula I use is:
L = .3927 [(D*D) - (d*d)]/T
L = length in inches
D = inside diameter of the barrel or space available for the mainspring to unwind, in inches
d = diameter of the arbor in inches
T = thickness of the mainspring in inches (not the width!)
(D*D) = D squared
With this formula you can vary the thickness of the mainspring a little (plus or minus 0.002" but favor the thinner side) and maybe find a suitable replacement.
For open springs, let D =the diameter of the mainspring wheel. The width will be determined by the depth of the barrel or the available amount of winding arbor. —bangster
Last edited by bangster; 04-04-2015 at 11:35 AM.
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