I have described above one of the methods in vogue for holding a staff by
means of wax. It is the common method employed by most watch repairers,
the popular method so to speak. The method which I am now about to
describe may seem awkward at first to those who have not practiced it,
but once you have fairly tried it, you will never be contented to work in
any other way.
The first requisite is a true taper chuck; and it is well to purchase an
extra one to be used solely for this purpose, so that you will be
prepared at all times for staff work. Select a good steel taper, and
having placed your chuck in the lathe, see if your taper fits well by
inserting it in the chuck while running slowly. If it fits well, it will
be marked almost throughout its length. Insert again in the chuck, and
with a few light taps of the hammer set it firmly in place, so that you
know that there is no danger of its working loose. The taper will then
project about three-quarters of an inch from the face of the chuck. By
means of a sharp graver, make the face of the taper smooth and straight,
and cut off the taper end. Now mark a point on the taper about one-fourth
of an inch from the end, and proceed to turn down the diameter from this
point to the end, leaving that portion of the taper about two-thirds of
its original diameter, and finish with a nice square shoulder. Now with
a long-pointed sharp graver proceed to cut a nice V-shaped center with an
angle of about 60 deg.. When you have proceeded thus far you will find that
you have an implement resembling that shown in Fig. 22.
[Illustration: _Fig. 22._]
Care must be taken that the center is quite true, and that no projection
is left like that illustrated in Fig. 21, no matter how minute it may be.
Now examine the center by the aid of a strong glass, and after you are
satisfied with its appearance proceed to test it. Take a large sized pin
with a good point, and placing the point in the center, maintain it in
position by pressing upon the head, and while revolving the lathe slowly
proceed to examine by means of your glass. If the center is a good one
there will be no perceptible vibration of the pin.
Now procure a piece of small brass tubing with an internal diameter a
little less than that of the turned down portion of your taper. If the
brass tubing cannot be procured readily, you can substitute a piece of
brass wire a little larger than the taper, and by means of a drill a
little smaller in diameter than the turned down portion you can readily
make a small tube about one-half inch long. Now by means of a broach
proceed to open the tube to a point one-quarter inch from one end, and
carefully fit it on the turned down portion of your taper. After fitting
tightly to the shoulder of the taper, proceed to turn out the other end
until it will take in the hub of your staff easily and leave a little
room to spare. Now turn your tube down in length until a little of the
hub is exposed either way you put the staff in. Turn the outside of the
tube smooth and to correspond with the outline of the taper, so you will
have a nice looking job when completed. Just below where the hub will
come drill a small hole in the tube and remove all burr, both inside and
out, that may have been made in drilling, so that the shellac or wax will
not adhere to it. This little hole acts as an outlet for the air in the
tube; and as the hot shellac enters at the end of the tube the air is
expelled through this vent. It also helps to hold the cement firmly in
place. Now try your staff in the tube again, and be sure that it is quite
free, and that you will be able to work on the portions of it above and
below the hub, according as one end or the other is inserted.
You are now ready to insert your staff and proceed with your work. Hold
your shellac in the flame of your lamp a moment until it is quite liquid,
and then smear both the inside and outside of the tube with it. Heat the
shell or tube gently by means of the lamp, keeping the lathe revolving
slowly all the while, and taking the staff in your tweezers proceed to
insert it carefully into the tube. Press firmly back, making sure that it
has reached the bottom of the V-shaped center. Pack the cement well in
around the staff, and while centering remove the lamp and allow the
whole to cool, keeping the whole revolving until quite cool. Now remove
the superfluous cement by means of the graver, and heating the tube again
slightly, proceed to center exactly by means of a pointed peg-wood,
resting on your T rest to steady it. Turn slowly in the lathe and examine
with glass to see that it is quite true. Your completed instrument will
resemble Fig. 23.
[Illustration: _Fig. 23._]
The advantage of the device is that your center is always ready, and all
you have to do is to insert your chuck in the lathe, warm it, and you are
ready to insert your staff and proceed to work. As I said in the first
place, it is well to employ a taper chuck exclusively for this work, and
not attempt to use it for any other, for if you try to remove your taper
and replace it again, you will surely find that your work is out of
center, and you will be compelled to remove the brass shell and find a
new center each time you use it. You can avoid all this trouble, however,
by purchasing an extra chuck and devoting it exclusively to wax work. Of
course, the brass shell can be removed and placed in position again
without in any way affecting the truth of the center, and any number,
shape and size of shells can be made to fit the one taper, and these
shells will be found very useful for holding a variety of work, aside
from balance staffs.