• <tt class='tlJykMlA'></tt>
  • <thead class='94K7Lauipx'><option class='9cNvbSu7LJ'></option></thead>

    <em class='jepytdnyfeW3'><b class='oR1Ys12nk'><td class='6rzzLTN'></td></b></em>

  • <dl class='Td0EmkF'><b class='qoWhaibfJ9'></b></dl>

  • <span class='lS1G'></span>


    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.

    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
    Number of Desired Turns of Barrel:
    Needed Mainspring Thickness:
    Needed Mainspring Length:
    NB = 
    NC x 
    P2 x WC
    WB x W2

    NB = 
    NC x 
    TMSn = 
    ( 2 x ( DB2 + DA2 ))½ - ( DB + DA )
    NB x 3/2
    LMSn = 
    2 x TMSn
    pi x DB2
    pi x DA2
    • 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.