Sidebar

log in bttn
join bttn

Calculate an Estimated Mainspring

If the mainspring is missing or if the existing mainspring is a suspect replacement, use this calculator to determine the correct sizing.

Change the items in the yellow boxes and see the Results below.

Calculator
Estimated Mainspring
Teeth in Movement:
 # of Wheels in Drive Train:
Wheel Teeth
Pinion Leaves
5 Wheels
Center Wheel or Center Pinion:
4 Wheels
2nd Wheel:
Main/Barrel Wheel:
Barrel Measurements:
 Expected Duration on a Full Wind
30 Hours
Inside Diameter of the Barrel:
8 Days
Diameter of the Barrel Arbor:
30 Days
Results:
Number of Desired Turns of Barrel:
Needed Mainspring Thickness:
Needed Mainspring Length:
Formulae:
NB = 
NC x 
P2 x WC
WB x W2

or,
NB = 
NC x 
WC
WB
TMSn = 
( 2 x ( DB2 + DA2 ))½ - ( DB + DA )
NB x 3/2
 x 
pi
8
LMSn = 
1
2 x TMSn
 x 
pi x DB2
4
 - 
pi x DA2
4
 )
where,
  • NB is the number of turns of the barrel
  • NC is the needed number of turns of the center wheel, i.e., number of hours: 30 or (8 days x 24) or (31 days x 24)
  • WB is the number of teeth on the barrel wheel
  • W2 is the number of teeth on the second wheel
  • WC is the number of teeth on the center wheel, or center pinion for a 4 wheel train
  • P2 is the number of leaves on the second wheel pinion
  • DB is the inside diameter of the barrel
  • DA is the outside diameter of the barrel arbor
  • TMS is the mainspring thickness
  • LMS is the mainspring length

5 Wheel Drive Train


4 Wheel Drive Train

This calculator, provided by Horology - The Index, is one in a series of repair calculations.



hal banner watchonista half banner timely half banner lwe half banner AHP