A gentleman on another site was having difficulty installing a new mainspring. Several people replied with possible answers but as everyone knows it's hard to diagnose a problem without the watch in-hand. I had him send the watch to me for a look-see.

From the symptoms he described, it appeared that the mainspring inner coil was not capturing the arbor hook. Each time he would attempt to wind the watch, it would wind about one turn and start slipping.

As depicted on the attached slide, the problem was found to be a slipping ratchet wheel. The wheel, arbor and screw will be replaced. The squares on the arbor could be filed but the wheel appears to be unusable.

Thanks for sharing this John, it,s something we could easily encounter someday.
Great slide and explanation here,Is this problem and slide going to be kept in your helping hand tutorials?

Chances are this watch was wound for a long time with a loose ratchet wheel screw, which allowed play and wear between the wheel and arbor, finally leading to the "rounding" of the square in the wheel.

Kevin - I keep all of my slides archived so they can be used for future tutorials.

Kenny - This is most likely a pre-existing condition. Someone in the past installed this screw which appears to have a head that is too small. By overtorquing the screw (note the screwdriver marks) the watch could be wound until it slipped one to many times.