A Treatise on Staff Making and Pivoting.

by Eugene E. Hall.

CHAPTER I.

To produce a good balance staff requires more skill than to produce any other turned portion of a watch, and your success will depend not alone on your knowledge of its proper shape and measurements, nor the tools at your command, but rather upon your skill with the graver and your success in hardening and tempering. There are many points worthy of consideration in the making of a balance staff that are too often neglected. I have seen staffs that were models as regards execution and finish, that were nearly worthless from a practical standpoint, simply because the maker had devoted all his time and energy to the execution of a beautiful piece of lathe work, and had given no thought or study to the form and size of the pivots. On the other hand, one often sees staffs whose pivots are faultless in shape, but the execution and finish so bungling as to offset all the good qualities as regards shape. To have good tools and the right ideas is one thing, and to use these tools properly and make a practical demonstration of your theory is another.

I shall endeavor to take up every point in connection with the balance staff, from the steel to the jewels, and their relation to the pivots, and I believe this will then convey to the reader all the necessary points, not only as regards staffs, but pivots also, whether applied to a balance or a pinion staff.

It may be argued, and we often do hear material dealers advance the theory, that to-day, with our interchangeable parts and the cheapness of all material, it is a waste of time to make a balance staff. To the reader who takes this view of the situation I simply want to say, kindly follow me to the end of this paragraph, and if you are still of the same opinion, then you are wasting your time in following me farther. For a material dealer to advance this theory I can find some excuse; he is an interested party, and the selling of material is his bread and b.u.t.ter; but the other fellow, well I never could understand him and possibly never shall. When we seriously consider the various styles and series in "old model" and "new model," of only one of the leading manufacturers of watches in this country, to say nothing of the legion of small and large concerns who are manufacturing or have manufactured in the past, and then think of carrying these staffs in stock, all ready for use, we then begin to realize how utterly absurd the idea is, to say nothing of how expensive! On the other hand, if you reside in a large city and propose to rely on the stock of your material dealer, you will find yourself in an embarrasing situation very often, for as likely as not the movement requiring a new staff was made by a company that went out of business back in the '80s, or it is a new movement, the material for which has not yet been placed on the market. This state of affairs leads to makeshifts, and they in turn lead to botch work. The watchmaker who does not possess the experience or necessary qualifications to make a new balance staff and make it in a neat and workmanlike manner, is never certain of having exactly what is needed, and cannot hope to long retain the confidence of his customers. In fact, he is not a watchmaker at all, but simply an apprentice or student, even though he be working for a salary or be his own master. There are undoubtedly many worthy members of the trade, who are not familiar with the making of a balance staff, who will take exceptions to this statement; but it is nevertheless true. They may be good workmen as far as they go; they may be painstaking; but they cannot be cla.s.sed as watchmakers.

This article is intended for the benefit of that large cla.s.s whose opportunities for obtaining instruction are limited, and who are ready and willing to learn, and for that still larger cla.s.s of practical workmen who can make a new staff in a creditable manner, but who are always glad to read others people's ideas on any subject connected with the trade and who are not yet too old to learn new tricks should they find any such.

[Ill.u.s.tration: _Fig. 1._]

Good tools, in good condition, are the most essential requisites in making a new staff. I would not advise any particular make of lathe, as the most expensive lathe in the world will not produce a true staff if the workman cannot center his work accurately and does not know how to handle his graver, while on the other hand fine work can be done on the simplest and cheapest lathe by a workman possessing the requisite skill.

I will take it for granted that you use an American-made lathe of some kind, or a foreign-made lathe manufactured on American lines. It is advisable, though not absolutely necessary, to have three gravers similar to those ill.u.s.trated in Fig. 1, A being used for turning the staff down in the rough; B for the conical pivots and square shoulders and C for the under-cutting. The other tools and attachments needed will be described as I come to them in use.

The balance staff should be made of the best steel, tempered to such a degree as to give the longest service and yet not so hard as to endanger the breakage of the pivots. Select a piece of Stubb's steel wire, say No.

46, or a little larger than the largest part of the finished staff is to be, and center it in a split chuck of your lathe. Be careful in selecting your chuck that you pick one that fits the wire fairly close. The chuck holds the work truest that comes the nearest to fitting it. If you try to use a chuck that is too large or too small for the work, you will only ruin the chuck for truth. Turn the wire to the form of a rough staff, as shown in Fig. 2, leaving on a small part of the original wire, as shown at A. After the wire is roughed out to this general form, remove from the chuck and get ready to harden and temper it. The hardening and tempering may be effected in various ways, and I am scarcely prepared to say which method is the best, as there are several which give about the same general results. One method of hardening is to smear the blank with common yellow soap, heat it to a cherry red, and drop endwise into linseed oil. Petroleum is preferred by some to linseed oil, but, to tell the truth, I can see no difference in the action of linseed, petroleum or olive oil. Be sure and have enough oil to thoroughly cool the blank, and a deep vessel, such as a large-mouthed vial, is preferable to a saucer.

The blank will now be found too hard to work easily with the graver, and we must therefore draw the temper down to that of fine spring steel.

Before doing this the blank should be brightened, in order that we may see to just what color we are drawing it. The main object in using the soap in hardening is that it may form a scale upon the blank, and if the heating is effected gradually the soap will melt and form a practically air-tight case around the blank. This scale, if the hardening is carefully and properly done, will generally chip and fall off when the blank is plunged in the oil, particularly if the oil is cool, and if it does not fall off of its own accord, it can easily be removed by rolling the blank upon the bench. If it does not come out clean, or if soap is not used, it may be brightened by again inserting in the lathe and bringing it in contact with a piece of fine emery paper or cloth.

[Ill.u.s.tration: _Fig. 2._]

I draw the temper in the following manner: Place some fine bra.s.s filings in a boiling-out cup or bluing pan and lay the blank upon these filings, holding the pan over the flame of an alcohol lamp until the blank a.s.sumes a dark purple color, which it will reach when the heat gets to about 500 F. This I consider the right hardness for a balance staff, as it is not too hard to work well under the graver nor too soft for the pivots. At this degree of hardness steel will a.s.sume an exquisite polish if properly treated. Another method of tempering is to place the staff on a piece of sheet iron or copper (say 1 inch wide by 4 long), having previously bent it into a small angle, for the reception of the staff, as shown in Fig.

3. This piece of metal, when nicely fitted into a file handle, will answer all the purposes of the bluing pan and presents quite a neat appearance. Having placed the blank in the angle, lay on it a piece of yellow wax about the size of a bean, and heat it over your lamp until the wax takes fire and burns. Blow out the flame and allow the staff to cool, and it will be found to be of about the right hardness.

[Ill.u.s.tration: _Fig. 3._]

We have now arrived at an important station in staff making, a junction, we may term it, where many lines branch off from the main road. At this particular spot is where authorities differ. I have no hesitation in saying that at this particular point the split chuck should be removed from the lathe head and carefully placed in the chuck box and the cement chuck put in its place. I believe that all of the remaining work upon a staff should be executed while it is held in a cement chuck. On the other hand I have seen good workmen who turned and finished all the lower part of a staff while in a split chuck, cut it off and turned and finished the upper part in a cement chuck. All I have got to say is that they had more confidence in the truth of their chucks than I have in mine. I have even read of watchmakers who made the entire staff in a split chuck, but I must confess I am somewhat curious to examine a staff made in that way, and must have the privilege of examining it before I will admit that a true staff can be so made.

We will suppose that the workman has a moderately true chuck, and that he prefers to turn and finish all the lower portions in this way. Of course the directions for using a cement chuck on the upper part of a staff are equally applicable to the lower. Before going further I think it advisable to consider the requirements of a pivot, but will reserve this for another chapter.

CHAPTER II.

The chief requirements of a pivot are that it shall be round and well polished. Avoid the burnish file at all hazards; it will not leave the pivot round, for the pressure is unequal at various points in the revolution. A pivot that was not perfectly round might act fairly well in a jewel hole that was round, but unfortunately the greater proportion of jewel holes are not as they should be, and we must therefore take every precaution to guard against untrue pivots. Let us examine just what the effect will be if an imperfect pivot is fitted into an unround hole jewel, and to demonstrate its action more clearly let us exaggerate the defects. Suppose we pick a perfectly round jewel and insert into the opening a three-cornered piece of steel wire, in shape somewhat resembling the taper of a triangular file. We find that this triangular piece of steel will turn in the jewel with the same ease that the most perfect cylindrical pivot will. Now suppose we change the jewel for one that is out of round and repeat the experiment. We now find that the triangular steel soon finds the hollow spots in the jewel hole and comes to a stand-still as it is inserted in the hole. The action of a pivot that is not true, when in contact with a jewel whose hole is out of round, is very similar, though in a less marked degree. If the pivot inclines toward the elliptical and the jewel hole has a like failing, which is often the case, it is very evident that this want of truth in both the pivot and hole is very detrimental to the good going of a watch.

[Ill.u.s.tration: _Fig. 4._]

[Ill.u.s.tration: _Fig. 5._]

There are two kinds of pivots, known respectively as straight and conical pivots, but for the balance staff there is but one kind and that is the conical, which is ill.u.s.trated in Fig. 4. The conical pivot has at least one advantage over the straight one, _i. e._, it can be made much smaller than a straight pivot, as it is much stronger in proportion, owing to its shape. All pivots have a tendency to draw the oil away from the jewels, and particularly the conically formed variety, which develops a strong capillary attraction. To prevent this capillary attraction of the oil, the back-slope is formed next to the shoulder, although many persons seem to think that this back-slope is merely added by way of ornament, to make the pivot more graceful in appearance. It is very essential, however, for if too much oil is applied the staff would certainly draw it away if its thickness were not reduced, by means of the back-slope. Before leaving the subject of capillarity let us examine the enlarged jewel in Fig. 5; _c_ is an enlarged pivot, _b_ is the hole jewel and _a_ is the end stone.

We observe that the hole jewel on the side towards the end stone is convex. It is so made that through capillarity the oil is retained at the end of the pivot where it is most wanted. It is, in my opinion, very necessary that the young watchmaker should have at least a fair understanding of capillarity, and should understand why the end stone is made convex and the pivot with a back slope. For this reason I will try and make clear this point before proceeding further. We all know that it is essential to apply oil to all surfaces coming in contact, in order to reduce the friction as much as possible, and if the application of oil is necessary to any part of the mechanism of a watch, that part is the pivot. Saunier very aptly puts it thus: "A liquid is subject to the action of three forces: gravity, adhesion (the mutual attraction between the liquid and the substance of the vessel containing it), and cohesion (the attractive force existing among the molecules of the liquid and opposing the subdivision of the ma.s.s.)"

We all know that if we place a small drop of oil upon a piece of flat gla.s.s or steel and then invert the same the oil will cling to the gla.s.s, owing to the adhesion of the particles; if we then add a little more to the drop and again invert, it will still cling, although the drop may be elongated to a certain degree. This is owing to the cohesion of the molecules of the oil, which refuse to be separated from one another. If, however, we again add to the drop of oil and invert the plate the drop will elongate and finally part, one portion dropping while the other portion clings to the main body of the liquid. The fall of the drop is occasioned by gravity overcoming the cohesion of the molecules. Now take a perfectly clean and polished needle and place a drop of oil upon its point and we will see that the oil very rapidly ascends towards the thicker portion of the needle. Now if we heat and hammer out the point of the needle into the form of a small drill and repeat the operation we find that the oil no longer ascends. It rises from the point to the extreme width of the drill portion, but refuses to go beyond. It clings to that portion of the needle which would correspond to the ridge just back of the slope in a conical pivot. Water, oil, etc., when placed in a clean wine gla.s.s, do not exhibit a perfectly level surface, but raise at the edges as shown at _a_ in Fig. 6. If a tube is now inserted, we find that the liquid not only rises around the outside of the tube and the edges of the vessel, but also rises in the tube far beyond its mean level, as shown at _b_. These various effects are caused by one of the forces above described, _i. e._, the adhesion, or mutual attraction existing between the liquid and the substance of the vessel and rod. The word capillarity is of Latin derivation, and signifies hair-like slenderness. The smaller the tube, or the nearer the edges of a vessel are brought together, the higher in proportion will the liquid rise above the level. An ascent of a liquid, due to capillarity, also takes place, where the liquid is placed between two separate bodies, as oil placed between two pieces of flat gla.s.s. If the plates are parallel to one another and perpendicular to the surface of the liquid it will ascend to the same height between the plates, as shown at _c_ in Fig. 6. If the plates were united at the back like a book and spread somewhat at the front, the oil would ascend the higher as the two sides approach one another, as shown at _d_, Fig. 6. If a drop is placed somewhat away from the intersecting point, of the gla.s.ses, as shown at _m_ it will, if not too far away, gradually work its way to the junction, providing the gla.s.ses are level. If, however, the gla.s.ses are inclined to a certain extent, the drop will remain stationary, since it is drawn in one direction by gravity and in the other by capillarity. When a drop of oil is placed between two surfaces, both of which are convex, or one convex and the other plain, as shown at _g_, it will collect at the point _n_, at which the surfaces nearest approach one another. We now see very clearly why the hole jewel is made convex on the side towards the end-stone and concave on the side towards the pivot.

[Ill.u.s.tration: _Fig. 6._]

Particular pains should be taken to polish those portions of the pivots which actually enter the jewel hole and to see that all marks of the graver be thoroughly removed, because if any grooves, no matter how small, are left, they act as minute capillary tubes to convey the oil.

If the hole jewel be of the proper shape, the end-stone not too far from the hole jewel and too much oil is not applied at one time, the oil will not spread nor run down the staff, but a small portion will be retained at the acting surface of pivot and jewel, and this supply will be gradually fed to these parts from the reservoir between the jewel and end-stone, by the action of capillarity.

Having examined into the requirements of the pivot and its jewel and having gained an insight into what their forms should be, we are the better able to perform that portion of the work in an intelligent manner.

CHAPTER III.

Our wire has been roughed out into the form of a staff, has been hardened and the temper drawn down to the requisite hardness and we are now ready to proceed with our work. As I said before, we have now arrived at a point where many authorities differ, _i. e._, as to whether the finishing of the staff proper, should be performed while the work is held in the chuck, or whether a wax chuck be subst.i.tuted. We will take it for granted that you have a true chuck and that you prefer to finish all the lower portion of the staff while held in the chuck.

Before we proceed with our work it will be necessary for us to make some accurate measurements, as we cannot afford to do any guess work by measuring by means of the old staff. I have used a number of different kinds of calipers and measuring instruments for determining the various measurements for a balance staff, but have met with more success with a very simple little tool which I made myself from drawings and description published some years ago in THE AMERICAN JEWELER. This simple little tool is shown in Fig. 7, and has been of great service to me. It consists of a bra.s.s sleeve A, with a projection at one end as shown at B. This sleeve is threaded, and into it is fitted the screw part C, which terminates in a pivot D, which is small enough to enter the smallest jewel. The sleeve I made from a solid piece of bra.s.s, turning it down in my lathe and finishing the projection by means of a file. The hole was then drilled and threaded with a standard thread. The screw part C, I made of steel and polished carefully.

[Ill.u.s.tration: _Fig. 7._]

To ascertain the proper height for the roller, place it upon the tool, allowing it to rest upon the leg B, and set the pivot D in the foot jewel. Now adjust, by means of the screw C until the roller is in its proper position in relation to the lever fork. This may be understood better by consulting Fig. 8, where A is the gauge, C is the roller, E is the lever, F is the plate and G is the potance.

[Ill.u.s.tration: _Fig. 8._]

Now in order to locate the proper place to cut the seat for the roller, remove it from the foot of the gauge and apply the gauge to the work as shown in Fig. 9. The foot of the gauge resting against the end of the pivot, the taper end of the gauge will locate accurately the position of the roller seat. In order to locate the proper position for the seat for the balance, proceed the same as for the roller, except that the foot of the gauge is lowered until it is brought sufficiently below the plate to allow of the proper clearance as indicated by the dotted lines at H. Now apply the gauge to the new staff, as shown in Fig. 10, and the taper end will locate the exact position for the balance seat.

[Ill.u.s.tration: _Fig. 9._]

[Ill.u.s.tration: _Fig. 10._]

As previously stated, I have taken it for granted that you preferred to finish all the lower portion of the staff while the work was held in the chuck. I have a.s.sumed that you prefer to work in this way because I have noted the fact that nine watchmakers out of every ten start with, and first finish up, the lower portion of the staff. Where this method of working originated I do not know, but it always has the appearance to me of "placing the cart before the horse." I do not pretend to say that a true staff cannot be made in this way, but it certainly is not the most convenient nor advisable. We all know that the heaviest part of the staff is from the roller seat to the end of the top pivot. Now it seems to me that it is the most natural thing in the world for a mechanic to desire to turn the greater bulk of his work before reversing it. Now if the workman has been educated to turn indifferently with right or left hand, it may make little difference, as far as the actual turning is concerned, whether he starts to work at the upper or lower end of the staff, but unfortunately there are few among us who are so skilled as to use the graver with equal facility with either hand, and it is therefore an advantage to start with the upper end, as you can thus finish a greater portion of the work more readily. You can readily see that when you come to reverse your staff and use the wax chuck, that by starting at the top of staff your wax has a much larger surface of metal to cling to, and again the shape of the balance seat is such as to secure the work firmly in the wax, while if the reverse method is employed, the larger portion of the balance seat is exposed and the staff is more liable to loosen from the motion of the lathe and pressure of the graver and polishers.

CHAPTER IV.

By the aid of the pinion calipers and the old staff, the diameter of the roller seat and the balance and hair-spring collet seats may be readily taken, but it is perhaps better to gauge the holes, as the old staff may not have been perfect in this respect. A round broach will answer admirably for this purpose, and the size may be taken from the broach by means of the calipers. In fitting our pivots, we can not be too exact; and as yet no instrument has been placed upon the market for this purpose which is moderate in price and yet thoroughly reliable. The majority of watchmakers use what is termed the pivot-gauge, a neat little instrument which accompanies the Jacot lathe, and which may be obtained from any material house. This tool, which is shown in Fig. 11, is, however, open to one objection in the measurement of pivots, and that is that it may be pressed down at one time with greater force than at another, and consequently will show a variation in two measurements of the same pivot.

Some of my readers may think that I am over-particular on this point, and that the difference in measurement on two occasions is too trivial to be worthy of attention, but I do not think that too much care can be bestowed upon this part of the work, and neglect in this particular is, I think, the cause of poor performance in many otherwise good timepieces. The ordinarily accepted rule among watchmakers is that a pivot should be made 1/2500 of an inch smaller than the hole in the jewel to allow for the proper lubrication. I am acquainted with watchmakers, and men who are termed good workmen, too, who invariably allow 1/2500 of an inch side shake, no matter whether the pivot is 12/2500 or 16/2500 of an inch in diameter. Now if 1/2500 of an inch is the proper side shake for a pivot measuring 12/2500 of an inch in diameter, it is certainly not sufficient for a pivot which is one-third larger. Of course it is understood that side shakes do not increase in proportion according as the pivot increases in size, for if they did a six-inch shaft would require at this rate a side shake of 1/2 inch, or 1/4 inch on each side, which would be ridiculously out of all proportion, as the 1/64 of an inch would be ample under any circ.u.mstances. Neither can we arrive at the proper end shake for a pivot by reducing in proportion from the end shake allowed on a six-inch shaft, because if we followed out the same course of reasoning we would arrive at a point where a pivot measuring 12/2500 of an inch would require an end shake so infinitely small that it would require six figures to express the denominator of the fraction, and the most minute measuring instrument yet invented would be incapable of recording the measurement. We must leave sufficient side shake, however, on the smallest pivot and jewel for the globules of the oil to move freely, and experiments have shown conclusively that 1/2500 of an inch or 1/5000 on each side of the pivot, is as little s.p.a.ce as it is desirable to leave for that purpose, as the globules of the best chronometer oil will refuse to enter s.p.a.ces that are very much more minute. But to return to our pivot gauge.

[Ill.u.s.tration: _Fig. 11._]

[Ill.u.s.tration: _Fig. 12._]

Each division on the gauge represents 1/2500 of an inch, which is all that we require. The diameter that the pivot should be, can be ascertained by inserting a round pivot broach into the jewel and taking the measurement with the pivot gauge, and then making the necessary deduction for side shake. Slip the jewel on the broach as far as it will go, as shown in Fig. 12, and then with the pivot gauge, take the size of the broach, as close up to the jewel as you can measure, and the taper of the broach will be about right for the side shake of the pivot. If, however, you prefer to make the measurement still more accurate, you can do so by dipping the broach into rouge before slipping on the jewel and then remove the jewel and the place which is occupied on the broach can be plainly discerned and the exact measurement taken and an allowance of 1/2500 of an inch made for the side shake. Another method, and one which is particularly applicable to Swiss watches, where the jewel is burnished into the c.o.c.k or plate, is to first slip on to the broach a small flat piece of cork and as the broach enters the jewel the cork is forced farther on to the broach, and when the jewel is removed it marks the place on the broach which its inner side occupied, and the measurement can then be taken with the gauge. If care is used in the selection of a broach, that it be as nearly perfect in round and taper as possible, by a little experiment you can soon ascertain just what part of the length of the broach corresponds to one degree on the gauge and by a repet.i.tion of the experiment the broach can then be divided accurately, by very minute rings turned with a fine-pointed graver, into sections, each representing one degree, or 1/2500 of an inch, and the measurement will thus be simplified greatly.

[Ill.u.s.tration: _Fig. 13._]