The two popular methods of holding a balance staff in wax have been
described and illustrated; the reader may take his choice. The turning
and finishing of the other end of the staff is performed as previously
described. That portion on which the hair-spring collet goes should be
turned to nearly the proper size, making due allowance for the grinding
and polishing that is to come. The balance seat should be slightly
undercut, so that the balance can be driven on tightly and all riveting
dispensed with. The size for the pivot can be determined from its jewel,
as previously described. Finish the ends of the pivots flat and round the
corners off slightly; and right here comes a point worthy of
consideration in all watch work. Leave no absolutely square corners in
any of your work, but round them off very slightly. This may seem a very
little thing, but it is one of the small things that go to make up
first-class work. You can judge pretty accurately of a watchmaker by the
corners he leaves on his work, as well as by the appearance of his
gravers and screw-drivers.
When your staff is completed and nicely polished, remove from the wax and
boil in alcohol to clean, and when dried it is ready for the balance.
Great care must be exercised in removing the balance from the old staff,
especially if it be a compensation balance, that you do not distort it
any way. If the balance has been riveted on extra care will have to be
exercised. The riveting may be cut by means of a graver, or a hollow
drill made from Stubb's steel wire. The recess in the drill should just
fit over the shoulder left for the reception of the hair-spring collet.
The edge of the hollow drill has small teeth formed upon it similar to a
fine file, and will cut quite rapidly.
After removing the balance, if it appears to be sprung in the arms, the
result of removal or previous bad treatment, proceed to bend them
straight, and then to true up the rim carefully, and stake on with a flat
end punch. Now put on your roller and drive it down to the hub and see
that the roller is free from the fork. See that jewel pin reaches fork
properly and that the guard pin also reaches the roller. See that your
balance is free from the plate and the bridge. If the balance is true and
all right, you are ready to put on your hair-spring. See that it is in
beat. It is well to make a mark on the balance before taking off the old
staff, showing positions of hair-spring stud and jewel pin.
Three-quarter plate English lever and Swiss lever balance staffs differ
only in detail, except that they are sprung under balances. The general
operations for making, however, are similar to those described.
I have not described the method of poising the balance for two reasons;
first, the mere poising of a balance for a cheap movement is so simple
that it needs no explanation; and second, to describe the poising of the
balance of a fine watch is a lengthy task, and can hardly be included
under the heading of staffing and pivoting. The ground has been
thoroughly and conscientiously covered by Mr. J. L. Finn, in a little
volume entitled Poising the Balance,[A] and I would advise all
watchmakers, both young and old, to read what he has to say.
Good pivoting is an art in itself, and although there are many who
undertake to do this work, there are but few who can pivot a staff in
such a manner that it will bear close inspection under the glass. We
often hear watchmakers brag of the secrets they possess for hardening
pivot drills, but I fancy they would be somewhat surprised if they
traveled around a little, to find how many watchmakers harden their
drills in exactly the same way that they do. The great secret, so-called,
of making good drills, is to first secure good steel, and then use care
to see that you do not burn it in the subsequent operations. The fewer
times the steel is heated the better. My experience teaches me that you
can do no better than to select some nice pieces of Stubb's steel for
your pivot drills. Many watchmakers make their drills from sewing
needles, say No. 3 or 4, sharps. The steel in these needles is usually of
good quality, but the great drawback is that a drill made from a needle
will not resist any great pressure, and is liable to break just at the
time that you have arrived at the most important point. If your drill is
made from a piece of Stubb's steel wire, or an old French or Swiss
graver, you not only know that the material in it is first-class, but you
can leave the base of the drill solid and substantial, with enough metal
in it to resist considerable pressure. The part of the drill which
actually enters the pivot is very short, and the end can be turned down
to the desired diameter. Turn or reduce your wire by means of a pivot
file so as to be smooth and conical, as shown at _A_, Fig. 24. The
conical form is given to the drill for exactly the same reason that it is
given to the balance pivots, because it gives additional strength. Heat
to a very pale red for about one-half inch from the end, and then spread
the point, as shown at _B_, Fig. 24, by a slight blow of the hammer. We
are now ready to temper our drill, and we must exercise a little care
that the steel is not burnt and that the drill is not bent or warped when
hardening. The flame of the alcohol lamp should be reduced as small as
possible, or otherwise the steel may become overheated and lose all its
good qualities. If needles are used for making drills there is a great
liability of their warping when hardening, but when a larger piece of
wire is used there is not much danger, if care is exercised in
introducing the drill that it goes into the compound straight and point
foremost. If a needle is used, it is well to construct a shield for it,
to be used when heating and hardening. This shield can be made from a
small piece of metal tubing, broached out to fit loosely over the shank
and point of the drill. The drill is introduced into this shield as shown
in Fig. 25, and a little soap may be introduced into the end _a_ before
plunging. Various hardening devices are used, but in my experience
beeswax or sealing wax will be found as good as any. Heat the drill (or
if a needle, the drill and shield both), to a pale red and plunge
straight into the wax. In the latter case, where the shield is used, the
shield, on striking the wax, will run up the shank of the drill, allowing
the point to pierce the wax. Some watchmakers introduce the extreme point
of the drill into mercury first and then plunge into the wax. This
hardens the extreme point of the drill very hard, so hard, in fact, that
it will penetrate the hardest steel, but care must be exercised with such
a drill because the mercury makes it not only very hard but very brittle.
_C_, Fig. 24, shows a drill after it has been finished on the Arkansas
stone. This shape of drill will withstand the pressure necessary to drill
into hard steel. Many watchmakers reduce the temper of every staff before
drilling. This, I think, is quite unnecessary. There are very few cases
in which it is necessary to reduce the temper of the staff, and even then
it should only be reduced as far as it is to be drilled, and then not in
excess of a good spring temper.
[Illustration: _Fig. 24._]
[Illustration: _Fig. 25._]
The centering of a staff in wax has been thoroughly described and in
pivoting the proceeding is the same as in staffing. After accurately
centering your work, make a small cut in the center for the reception of
the drill and make this mark deep enough to take the entire cutting head
of the drill. Keep the drill firmly pressed into this center and kept wet
constantly with turpentine. Do not revolve the work all one way, but give
the lathe an alternating motion. At first give but a third or a half
revolution each way, until the drill begins to bite into the staff, when
you can then safely give it a full revolution each way. Care must be
exercised, however, not to give the work too rapid a motion, for if you
do the friction is apt to draw down the temper of your drill. Many
watchmakers find that their drills cut well for a certain distance and
then refuse to work altogether, and one of the chief reasons is that they
are in too great a hurry with their drilling.
If you find it absolutely necessary to reduce the hardness of your staff
before drilling, do so by drilling a hole in the end of a small piece of
copper wire that will just fit over the part to be softened, and apply
the heat to this copper wire, say one-fourth of an inch from the staff.
The heat will run down the copper wire and heat the staff just where you
wish to draw the temper. Be careful and do not draw the temper too much,
nor let it extend down the staff too far.
The plug for the new pivot should be carefully made, perfectly round,
with a very little taper, and should be draw-filed before being driven
in. Some workmen dip the plug in acid before driving in, as they declare
that the pivot is less liable to be loosened while turning, if so
treated. The acid simply rusts the pivot and the hole, but I cannot see
that this will hold it any more firmly in place while finishing. If the
taper is a gradual one and the pivot a good close fit, there will be
little danger of it loosening while dressing to shape. If too great a
taper is given to the plug, there is danger of splitting the end of the
staff, and this involves the making of an entire new staff.
The turning up of a new pivot does not differ in any way from the
instructions given for turning pivots on a new staff. With a little care
both in turning and finishing, a new pivot can be put in so nicely that
only the initiated can tell it, and then only with the aid of a strong
glass.
In pivoting cylinders there is some danger of breaking them. To avoid
this, select a piece of joint wire, the opening of which is slightly
larger than the diameter of the cylinder at the lower end, and cut off a
piece the length of the cylinder proper, leaving the pivot projecting.
Now fill the cylinder with lathe wax, and while the wax is warm, slip on
the joint wire. You can now proceed to true up the pivot in the usual
manner, and when the wax is quite cold, proceed to turn and polish the
pivot before removing from the lathe. If the joint wire is properly
cemented on the cylinder, it is almost impossible to break it. After all
the work is done, the wax can be dissolved in alcohol. In pivoting
pinions to cylinder escape-wheels and third wheels, it is not necessary
to remove the wheels, but great care should be used in handling. In the
latter case use plenty of wax. Do all your centering by the outside of
the pinion. Perfect centering and sharp tools are requisite to good
pivoting. Do not try to rush your work, especially while drilling.
Proceed deliberately with your work and aim to restore the watch to the
condition it was in originally, and you will find staffing and pivoting
is not half as hard as some workmen would have you believe.
[Footnote A: POISING THE BALANCE, by J. L. Finn, Geo. K. Hazlitt & Co.,
publishers, Chicago.]