Balance Staff
The axis or staff to which the balance is attached. In some makes of watches the balance staff and collet are one piece, while in others the collet is made of brass and is fitted tightly to the staff. Making a New Staff. It is a very common thing for American workman, especially those who reside in the large cities, to depend upon the stock of the material dealer for their staffs. The country watch-maker must, however, rely upon his mechanical ability, and even in the large cities the workman will have to make his own staffs when repairing many foreign watches. The following instructions relate more particularly to staffs for American watches, though they may be applied to foreign watches as well. Before proceeding further I would call the attention of the trade to a most valuable series of essays on the balance staff, published in the columns of The American Feweler, and would advise those interested to read them carefully (Making and Replacing the Balance Staff, a series of seventeen essays published in The American Feweler for December, 1888, and January to September, 1889, inclusive, The Illustrations are from these essays.) The material used should be the best, say Stubb's steel wire, a little larger in diameter than the largest part of the staff and a trifle longer than the old one. A wire that fits the No. 45 hole in the pinion gauge will be about right in the majority of cases. Put this in the split chuck of your lathe, if you use an American lathe, and rough it out to the form shown at B in Fig. 18. If you use a Swiss or wax-chuck lathe, the form of chuck shown at A, Fig. 18, will be found very useful. (From the essay by "Pasadena," American Feweler March, 1889.) It is made from a piece of brass rod, threaded to fit the lathe spindle and bored out to receive the work, which is held by set screws, three or four at each end of the chuck. By the aid of these screws the work may be held very firmly and yet can easily be brought to center. After bringing the work to the general form of the staff, in the rough, remove from the lathe, smear with soap and harden by heating to a cherry red and plunge endwise into oil. Re chuck in the lathe, and while revolving, whiten by applying a No.ooo emery buff, so that you may observe the color while drawing the temper. Now place the roughed-out blank in the bluing pan, and draw to a deep blue in color.
The heights may be taken from the old staff, providing it was not faulty and is at hand, but all things considered it is better to make your measurements and construct the new staff independent of the old one. A simple tool, and one which any watchmaker can make, is shown in Fig. 19. It will be found very convenient in taking the measurements of heights of a staff. (Other measuring instruments for this purpose will be found under Gauges.) It consists of a hollow sleeve A, terminating in a foot B. Through this is screwed the rod C, terminating in a pivot D, which is small enough to enter the smallest jewel. To ascertain the right height for the roller, place it upon the foot B, indicated in Fig. 20, and set the pivot of the tool in the foot jewel, and adjust the screw until the roller is in the proper relation to the lever fork as shown in the illustration. In, Fig. 20 the potence and plate of the watch are shown in section at A. The roller is indicated at c and the lever fork at d. After the adjusting of the roller is completed, remove the tool and apply it to the rough staff as indicated in Fig. 21, at A, and the point at which the seat for the roller should be cut will be shown. In order to ascertain the height of the balance, apply the gauge as before and bring the point e, so as to give sufficient clearance below the plate as indicated by the dotted lines at B, Fig. 20. Then apply the gauge to the work as indicated at B, Fig. 21, and turn the balance seat at the point indicated. The diameter of the seat for the roller, balance and hairspring collet, can be taken from the old staff, of gauge the holes with a taper arbor or a round broach, and then take the size from the broach with calipers.
The diameter of the lower pivot should be taken from the jewel, and the ordinary pivot gauge, when used in connection with a round pivot broach, is all that is necessary even for the finest work. At A, in Fig. 22, is shown the gauge, each division of which corresponds to about 1/2500 of an inch. Slip the jewel on the broach as far as it will go without forcing, as shown at B, Fig. 22, and then take the size of the broach, close up to the jewel, by means of the slit in the gauge. This will not give you the exact size of the jewel hole, but will be just enough smaller to allow of the proper freedom of the pivot.
The best shape for the pivots is shown in Fig. 23, known as conical pivots; the straight portion of the pivot which enters the jewel hole being truly cylindrical and about 1/100 of an inch long. Many very good workmen employ but one graver for performing the entire work, but it is better to have at least three, similar in shape to those shown in Fig. 23; A for turning the staff down in the rough, B for under-cutting, and C for turning the conical shoulders of the pivots. A graver like that shown at D will be found excellent for beginners and others who find it difficult to hold the shoulder square and at right angles to the staff E, without leaving a groove in one or the other. The all important thing is to keep the gravers sharp. Upon the least sign of their not cutting, stop the work and sharpen them.
Next in importance is the position in which the graver is applied to the work. It must, under all circumstances, cut and not scrape. If held as shown at A, Fig. 25, it will cut a clean shaving, while if applied as at B, it will only scrape. If held as shown at C, the force of the cut will be in the direction of the hand, as indicated by the arrow. If the point should catch from any cause, the hand would yield and no harm would be done, while if held as at D, the force of the cut would be downward upon the rest, as indicated by the arrow, and the rest being unyielding catching would be dangerous. The roughing out should be done with the point of the graver held as at C, Fig. 25, and then finished with the edge held diagonally as at A, Fig. 26. It is difficult to show the exact position in the cuts, but the idea is to have the shavings come away in a spiral may be as fine as a hair, but in perfect coils.
To turn the pivot, hold the graver nearly in line with the axis of the lathe, as shown at B, Fig 26, and catching a chip at the extreme end with the back edge of the graver, push forward and at the same time rolling the graver towards you, which will give the pivot the conical form. Very small pivots can be turned in this way with perfect safety, and very smoothly. Of course, this method of turning will not give sharp corners; such places as the seat of the roller, balance, etc., must be carefully done with the point of the graver. The pivot and seat of the roller should be left slightly larger than required, to allow for the grinding and polishing, the amount of which will depend upon how smoothly the turning is done. The grinding is done with a slip of bell-metal or soft iron or steel of the shape shown at A, Fig. 27. B is a bell-metal polisher, and may also be made of box wood. A should be used with oil-stone powder and oil, and B with crocus and diamantine for polishing. When the staff is finished from the lower pivot to the seat of the balance, the upper part should be roughed out nearly to size, then cut off, reversed in the lathe and the top part finished. It is better to do this in a wax chuck even if you use a split chuck, for the lower part of the staff is tapered and it is ten chances to one that you could select a split chuck that would hold it true and firm. In using a wax chuck the important point is to get a perfect center. it should be turned out with the graver at an angle of about 60 deg., care being taken not to leave a little "tit" in the center. Before setting the staff in the wax it is necessary to get its full length as follow: Screw the balance cock in place with both cap jewels removed, and if the cock has been bent up or down, or punched to raise or lower it, see that it is straightened and put right; then with a degree gauge or calipers take the distance between the outer surfaces of the hole jewels, and shorten the staff with a file to that length.
A very handy tool can be made by adding a stop-screw to the common double calipers as shown in Fig. 28. The improvement is that they can be opened to remove from the work and closed again exactly the same. When fixing the staff in the chuck, care should be taken not to burn the wax. Use a small lamp and heat the chuck until the wax will just become fluid. The staff should be set in the wax about to the seat of the balance, the finished pivot resting in the center of the chuck, and the outer end trued up by the finger and the point of a peg while the wax is still soft. Fig. 29 shows it with the staff finished, but, of course, it is not, when put in the wax. The dotted lines show about the right quantity and shape of the wax, which must be true and round, or in cooling it will draw the work out of center. If necessary, when cool, the wax can be turned true with the graver, again heated and centered. The turning and finishing is to be done as previously described. The seat for the balance should be slightly undercut and fitted to drive on tightly without riveting. Take the size of the top pivot from its jewel the same as the lower. The ends of the pivots should be finished as flat as possible, and the corners slightly rounded. When done, remove from the wax and boil in alcohol to clean, and it is ready to receive the balance, which should first be poised as described on page 27.