Why So Many Crowns Are Lost
Fix a crown with a thin surface or side to a winding-stem and fasten the stem either to a watch or to a mandril. Then strike a few time, even very lightly with a small brush, for instance, and you will see for yourself how easy it is to free the crown. After that, it will become completely unscrewed in a very short time. It is evident that a thin surface will bend at the slightest shock, and it is just at this time that the thread of the screw of the crown will not adhere closely to the screw of the stem.
It is natural, on the other hand, that the screw-thread of the winding stem should be similar to that of the crown, for it is impossible to fix a crown to a winding-stem if the screw-thread be too thin.
I have often been able to ascertain that the apparently simple work of fixing the crown to the winding stem often presents important stumbling blocks.
It is an error to maintain the winding stem in a mandril when fixing the crown. In proceeding in this way, it is impossible not to break the winding-stem, for, as shown clearly in illustration 5, the pressure of the tongs of the mandril is exercised only on the most delicate part of the winding-stem, that is the notch for the setting-lever. It is certainly aggravating, at the last minute, to break a stem which has just been finished with much care and attention. But even if the stem should not break, it is a mistake to use the mandril, for it often leaves rough ridges, which once the stem is in place, act as reamers on the plate. Shortly after, the stem begins to "dance," the setting lever is not supported as it should, and when the hands are set, the stem falls out. If this happens with watches of well-known trade marks it is all the more disagreeable because of the fact that it will never be possible to use a winding-stem to fix the crown properly again.
I would recommend the use of the Seitz pliers, which can be obtained from Messrs. Bergeon of Le LocIe. I have made three pliers, adapted to a point similar to that illustrated in fig. 6. The reader will easily see that this point allows the fixing of the superior part of the winding-stem, avoiding all risks of a breakage. A second advantage is the fact that this tool avoids all risks of causing marks of any kind on the stem, as indicated above. I have these pliers in Nos. 8, 10, 12, which is largely sufficient for nearly all the work to be done on wrist watches.
I have been able to note that errors of this kind are made not only by small watch repairers, but also in large factories, where careful attention is paid to the execution of their products, but where insufficient care is taken in mounting the crown.