There are two princ.i.p.al causes for the difficulty. One is due to the back of discharging pallet stone having a very sharp corner combined with a slightly rough edge on the back of the escape wheel teeth and when the two factors meet with some slight force, such as is caused by reversal of the train wheels the sharp corner of the stone wedges itself into the rough surface of the tooth and holds until pulled away by some small instrument. This can be remedied by removing the sharp edge of the stone on a diamond charged polishing lap and a very slight correction is sufficient.

The second princ.i.p.al cause is due to sharp edges on the roller jewel.

First quality roller jewels always have these edges rounded, as otherwise they may wedge into the horn of the fork and often will not release through ordinary shaking of the watch.

A short guard pin can also cause the trouble by allowing the roller jewel to catch on the end of the fork horn before it enters, or the guard pin may catch on the edge of the crescent on the safety roller, but the two causes mentioned above will allow "hanging up" even when the guard pin, roller jewel and all other shakes are correct.

When the above conditions are correct and all setting connections are properly fitted, the hands may be set either forward or backward without in any way disturbing the time. There are instances, however, where the watch will stop when the hands are reversed and at times the second hand will actually turn backward although the watch will immediately begin to run as soon as the backward pressure on the hands is discontinued.

This is caused by the cannon pinion being so tightly fitted that turning it backward will require more force than that which is supplied by the mainspring. A condition of this description is more p.r.o.nounced when the mainspring is nearly run down and sometimes it will happen at such times and will not occur when the spring is fully wound.

85. _Essentials and Non-Essentials in Cleaning Watches._

It would be difficult to suggest a best method for general cleaning of watches. Different watchmakers have different methods and good results are attained in more than one way. Whatever the method, however, there are certain definite requirements that are fundamental.

Among these are the thorough cleansing of pivots, jewels, pinion leaves, wheel teeth, mainspring and winding parts.

It is not sufficient to depend upon routine and simply dip the parts in various solutions, brush and rea.s.semble the watch. There are many instances in which the oil becomes gummy and sticks to the jewels and pivots to such an extent that peg wood and pith must be applied with considerable energy to obtain perfectly clean surfaces and holes.

The essential feature is that of actually removing every particle of dirt from the contact surface.

It is not essential that the plate and bridges should have a high l.u.s.tre, as this does not facilitate the running. If it is desired and if facilities are available, the plates and bridges may be dipped in benzine and dried in sawdust, then washed and brushed in a solution of hot water, borax and castile soap, then rinsed in fresh water, dipped in alcohol and dried in sawdust. This produces a l.u.s.tre to the plate bridges and wheels. When it is not convenient to use hot water the parts may be dipped and brushed in benzine for at least one minute and dried in sawdust, then dipped in alcohol and again dried in sawdust.

In either event thorough pegging and pithing of the jewels, pivot holes and pivots is necessary as well as brushing and examining all wheel teeth and pinion leaves. The steel parts should be examined and gummy oil eliminated. Fresh oil should be applied in proper quant.i.ties in the proper places. This requires some study, as either too much or too little oil is detrimental.

When a watch is cleaned annually by the same workman it is not necessary that the mainspring be removed and reoiled each time, for a mainspring properly oiled will last for two or three years before requiring cleaning and reoiling.

It is well known that mainsprings frequently break shortly after being removed and cleaned and this annoyance may be avoided in many instances by intelligent use of this rule.

Balances should not be dipped in acid solutions, as the liquid gathers under the screws and will often cause them to discolor in a short time. It is better to polish them with fine rouge and cotton thread arranged on a wire bow as the l.u.s.tre will be more lasting.