In attaching the collet it is first necessary to have the spring level before the pin is forced tightly in place. This can be fairly well determined by sighting across the flat of the spring and focusing upon the inner coil to see that it is level for at least one half of its length from the point of exit. After this operation has been completed and the pin has been set up tight, with the surplus ends cut off flush with the collet it will be necessary to slightly pull the coil up or down, providing it is not perfectly level. The next operation will be that of truing the round and all work and bending of the spring for this operation is concentrated within the first quarter of the coil from its point of attachment and it is seldom ever necessary to make any bends beyond the first eighth of the coil from the attached point.
Figure 28 may be of some value in gaining an idea as to just how this inner coil should appear when it has been trued.
The broken lines illustrate a condition after colleting and before truing. The heavy lines illustrate two positions into either of which the coil may be formed in getting the spring true.
Fig. 28
The outer black line shows the most adaptable form for most instances. The inner black line shows the most practical form for use in instances where there is unusual space between the collet and the inner coil. It will be noted that these two forms blend into the true spiral form of the spring at about one-eighth of the coil distant from the collet. These forms may be used as a basis for truing the spring in any instance in which it has been bent or mishandled around the collet after its original truing.
Experts always true springs after they have been staked to the balance and a light weight calipers tapered on one end to a smaller diameter than the collet is used for spinning the balance, making observations, and corrections.
Considerable progress can be made by some watchmakers in removing the spring from the balance and placing it on a colleting tool or tapered broach and then truing the flat and round as good as possible, after which it should be perfected in the calipers. When the balance is spinning in the calipers and the spring is true in the flat there will be no jumping or quivering of the coils as observation is made across the top of the inner four or five coils.
When it is perfectly true in the round and the balance is spinning in one direction the coils will seem to be whirling into a hole of which the collet is the center. When spinning the balance in the opposite direction the effect of the coils will be similar to the waves produced by dropping a small stone in still water and they will appear to be whirling away from the center. This effect in both instances is caused by the eye following the spiral form of the coils as the spring revolves.