In turning the staffs it is the best plan to use double centers, but a piece of Stubs steel wire that will go into a No. 40 wire chuck, will answer; in case such wire is used, a bra.s.s collet must be provided. This will be understood by inspecting Fig. 30, where _L_ represents the Stubs wire and _B N_ the bra.s.s collet, with the balance seat shown at _k_. The escape-wheel arbor and pallet staff can be made in the same way. The lower end of the escape wheel pivot is made about " long, so that a short piece of bra.s.s wire can be screwed upon it, as shown in Fig. 31, where _h_ represents the pivot, _A_ the lower plate, and the dotted line at _p_ the bra.s.s piece screwed on the end of the pivot. This piece _p_ is simply a short bit of bra.s.s wire with a female screw tapped into the end, which screws on to the pivot. An arm is attached to _p_, as shown at _T_. The idea is, the pieces _T p_ act like a lathe dog to convey the power from one of the pivots of an old eight-day spring clock movement, which is secured by screws to the lower side of the main plate _A_. The plan is ill.u.s.trated at Fig. 32, where _l_ represents pivot of the eight-day clock employed to run the model. Counting the escape-wheel pivot of the clock as one, we take the third pivot from this in the clock train, placing the movement so this point comes opposite the escape-wheel pivot of the model, and screw the clock movement fast to the lower side of the plate _A_. The parts _T_, Fig. 33, are alike on both pivots.

[Ill.u.s.tration: Fig. 32]

[Ill.u.s.tration: Fig. 33]

PROFITABLE FOR EXPLAINING TO A CUSTOMER.

To fully appreciate such a large escapement model as we have been describing, a person must see it with its great balance, nearly 4"

across, flashing and sparkling in the show window in the evening, and the brilliant imitation ruby pallets dipping in and out of the escape wheel. A model of this kind is far more attractive than if the entire train were shown, the mystery of "What makes it go?" being one of the attractions. Such a model is, further, of great value in explaining to a customer what you mean when you say the escapement of his watch is out of order. Any practical workman can easily make an even $100 extra in a year by making use of such a model.

For explaining to customers an extra balance c.o.c.k can be used to show how the jewels (hole and cap) are arranged. Where the parts are as large as they are in the model, the customer can see and understand for himself what is necessary to be done.

It is not to be understood that our advice to purchase the jewels for an extra balance c.o.c.k conflicts with our recommending the reader not to jewel the holes of his model. The extra c.o.c.k is to be shown, not for use, and is employed solely for explaining to a customer what is required when a pivot or jewel is found to be broken.

HOW LARGE SCREWS ARE MADE.

The screws which hold the plates in place should have heads about 3/8"

in diameter, to be in proportion to the scale on which the balance and escape wheel are gotten up. There is much in the manner in which the screw heads are finished as regards the elegance of such a model. A perfectly flat head, no matter how highly polished, does not look well, neither does a flattened conehead, like Fig. 35. The best head for this purpose is a cupped head with chamfered edges, as shown at Fig. 34 in vertical section. The center _b_ is ground and polished into a perfect concave by means of a metal ball. The face, between the lines _a a_, is polished dead flat, and the chamfered edge _a c_ finished a trifle convex. The flat surface at _a_ is bright, but the concave _b_ and chamfer at _c_ are beautifully blued. For a gilt-edged, double extra head, the chamfer at _c_ can be "snailed," that is, ground with a suitable lap before bluing, like the stem-wind wheels on some watches.

[Ill.u.s.tration: Fig. 34]

[Ill.u.s.tration: Fig. 35]

FANCY SCREWHEADS.

There are two easy methods of removing the blue from the flat part of the screwhead at _a_. (1) Make a special holder for the screw in the end of a cement bra.s.s, as shown at _E_, Fig. 36, and while it is slowly revolving in the lathe touch the flat surface _a_ with a sharpened pegwood wet with muriatic acid, which dissolves the blue coating of oxide of iron. (2) The surface of the screwhead is coated with a very thin coating of sh.e.l.lac dissolved in alcohol and thoroughly dried, or a thin coating of collodion, which is also dried. The screw is placed in the ordinary polishing triangle and the flat face at _a_ polished on a tin lap with diamantine and oil. In polishing such surfaces the thinnest possible coating of diamantine and oil is smeared on the lap--in fact, only enough to dim the surface of the tin. It is, of course, understood that it is necessary to move only next to nothing of the material to restore the polish of the steel. The polishing of the other steel parts is done precisely like any other steel work.

[Ill.u.s.tration: Fig. 36]

The regulator is of the Howard pattern. The hairspring stud is set in the c.o.c.k like the Elgin three-quarter-plate movement. The richest finish for such a model is frosted plates and bridges. The frosting should not be a fine mat, like a watch movement, but coa.r.s.e-grained--in fact, the grain of the frosting should be proportionate to the size of the movement. The edges of the bridges and balance c.o.c.k can be left smooth.

The best process for frosting is by acid. Details for doing the work will now be given.

[Ill.u.s.tration: Fig. 37]

[Ill.u.s.tration: Fig. 38]

To do this frosting by acid nicely, make a sieve by tacking and gluing four pieces of thin wood together, to make a rectangular box without a bottom. Four pieces of cigar-box wood, 8" long by 1" wide, answer first rate. We show at _A A A A_, Fig. 37, such a box as if seen from above; with a side view, as if seen in the direction of the arrow _a_, at Fig. 38. A piece of India muslin is glued across the bottom, as shown at the dotted lines _b b_. By turning up the edges on the outside of the box, the muslin bottom can be drawn as tight as a drum head.

HOW TO DO ACID FROSTING.

To do acid frosting, we procure two ounces of gum mastic and place in the square sieve, shown at Fig. 37. Usually more than half the weight of gum mastic is in fine dust, and if not, that is, if the gum is in the shape of small round pellets called "mastic tears," crush these into dust and place the dust in _A_. Let us next suppose we wish to frost the c.o.c.k on the balance, shown at Fig. 39. Before we commence to frost, the c.o.c.k should be perfectly finished, with all the holes made, the regulator cap in position, the screw hole made for the Howard regulator and the index arc engraved with the letters S and F.

[Ill.u.s.tration: Fig. 39]

It is not necessary the bra.s.s should be polished, but every file mark and scratch should be stoned out with a Scotch stone; in fact, be in the condition known as "in the gray." It is not necessary to frost any portion of the c.o.c.k _C_, except the upper surface. To protect the portion of the c.o.c.k not to be frosted, like the edges and the back, we "stop out" by painting over with sh.e.l.lac dissolved in alcohol, to which a little lampblack is added. It is not necessary the coating of sh.e.l.lac should be very thick, but it is important it should be well dried.

HOW TO PREPARE THE SURFACE.

For ill.u.s.tration, let us suppose the back and edges of the c.o.c.k at Fig.

39 are coated with sh.e.l.lac and it is laid flat on a piece of paper about a foot square to catch the excess of mastic. Holes should be made in this paper and also in the board on which the paper rests to receive the steady pins of the c.o.c.k. We hold the sieve containing the mastic over the c.o.c.k and, gently tapping the box _A_ with a piece of wood like a medium-sized file handle, shake down a little snowstorm of mastic dust over the face of the c.o.c.k _C_.

Exactly how much mastic dust is required to produce a nice frosting is only to be determined by practice. The way to obtain the knack is to frost a few sc.r.a.ps to "get your hand in." Nitric acid of full strength is used, dipping the piece into a shallow dish for a few seconds. A good-sized soup plate would answer very nicely for frosting the bottom plate, which, it will be remembered, is 6" in diameter.

HOW TO ETCH THE SURFACE.

After the mastic is sifted on, the c.o.c.k should be heated up to about 250 F., to cause the particles of mastic to adhere to the surface. The philosophy of the process is, the nitric acid eats or dissolves the bra.s.s, leaving a little bra.s.s island the size of the particle of mastic which was attached to the surface. After heating to attach the particles of mastic, the dipping in nitric acid is done as just described. Common commercial nitric acid is used, it not being necessary to employ chemically pure acid. For that matter, for such purposes the commercial acid is the best.

After the acid has acted for fifteen or twenty seconds the bra.s.s is rinsed in pure water to remove the acid, and dried by patting with an old soft towel, and further dried by waving through the air. A little turpentine on a rag will remove the mastic, but turpentine will not touch the sh.e.l.lac coating. The surface of the bra.s.s will be found irregularly acted upon, producing a sort of mottled look. To obtain a nice frosting the process of applying the mastic and etching must be repeated three or four times, when a beautiful coa.r.s.e-grain mat or frosting will be produced.

The sh.e.l.lac protection will not need much patching up during the three or four bitings of acid, as the turpentine used to wash off the mastic does not much affect the sh.e.l.lac coating. All the screw holes like _s s_ and _d_, also the steady pins on the back, are protected by varnishing with sh.e.l.lac. The edges of the c.o.c.ks and bridges should be polished by rubbing lengthwise with willow charcoal or a bit of chamois skin saturated with oil and a little hard rouge scattered upon it. The frosting needs thorough scratch-brushing.

[Ill.u.s.tration: Fig. 40]

At Fig. 40 we show the balance c.o.c.k of our model with modified form of Howard regulator. The regulator bar _A_ and spring _B_ should be ground smooth on one side and deeply outlined to perfect form. The regulator cap _C_ is cut out to the correct size. These parts are of decarbonized cast steel, annealed until almost as soft as sheet bra.s.s. It is not so much work to finish these parts as one might imagine. Let us take the regulator bar for an example and carry it through the process of making.

The strip of soft sheet steel on which the regulator bar is outlined is represented by the dotted outline _b_, Fig. 41.

[Ill.u.s.tration: Fig. 41]

To cut out sheet steel rapidly we take a piece of smooth clock mainspring about " and 10" long and double it together, softening the bending point with the lamp until the piece of mainspring a.s.sumes the form shown at Fig. 42, where _c_ represents the piece of spring and _H H_ the bench-vise jaws. The piece of soft steel is placed between the limbs of _c c'_ of the old mainspring up to the line _a_, Fig. 41, and clamped in the vise jaws. The superfluous steel is cut away with a sharp and rather thin cold chisel.

[Ill.u.s.tration: Fig. 42]

The chisel is presented as shown at _G_, Fig. 43 (which is an end view of the vise jaws _H H_ and regulator bar), and held to cut obliquely and with a sort of shearing action, as ill.u.s.trated in Fig. 42, where _A''_ represents the soft steel and _G_ the cold chisel. We might add that Fig. 42 is a view of Fig. 43 seen in the direction of the arrow _f_. It is well to cut in from the edge _b_ on the line _d_, Fig. 41, with a saw, in order to readily break out the surplus steel and not bend the regulator bar. By setting the pieces of steel obliquely in the vise, or so the line _e_ comes even with the vise jaws, we can cut to more nearly conform to the circular loop _A''_ of the regulator _A_.

[Ill.u.s.tration: Fig. 43]

The smooth steel surface of the bent mainspring _c_ prevents the vise jaws from marking the soft steel of the regulator bar. A person who has not tried this method of cutting out soft steel would not believe with what facility pieces can be shaped. Any workman who has a universal face plate to his lathe can turn out the center of the regulator bar to receive the disk _C_, and also turn out the center of the regulator spring _B_. What we have said about the regulator bar applies also to the regulator spring _B_. This spring is attached to the c.o.c.k _D_ by means of two small screws at _n_.

The micrometer screw _F_ is tapped through _B''_ as in the ordinary Howard regulator, and the screw should be about No. 6 of a Swiss screw-plate. The wire from which such screw is made should be 1/10" in diameter. The steel cap _C_ is fitted like the finer forms of Swiss watches. The hairspring stud _E_ is of steel, shaped as shown, and comes outlined with the other parts.

TO TEMPER AND POLISH STEEL.

The regulator bar should be hardened by being placed in a folded piece of sheet iron and heated red hot, and thrown into cold water. The regulator bar _A A'_ is about 3" long; and for holding it for hardening, cut a piece of thin sheet iron 2" by 3" and fold it through the middle lengthwise, as indicated by the dotted line _g_, Fig.

44. The sheet iron when folded will appear as shown at Fig. 45. A piece of flat sheet metal of the same thickness as the regulator bar should be placed between the iron leaves _I I_, and the leaves beaten down with a hammer, that the iron may serve as a support for the regulator during heating and hardening. A paste made of castile soap and water applied to the regulator bar in the iron envelope will protect it from oxidizing much during the heating. The portions of the regulator bar marked _h_ are intended to be rounded, while the parts marked _m_ are intended to be dead flat. The rounding is carefully done, first with a file and finished with emery paper. The outer edge of the loop _A''_ is a little rounded, also the inner edge next the cap _C_. This will be understood by inspecting Fig. 46, where we show a magnified vertical section of the regulator on line _l_, Fig. 40. The curvature should embrace that portion of _A''_ between the radial lines _o o'_, and should, on the model, not measure more than 1/40". It will be seen that the curved surface of the regulator is sunk so it meets only the vertical edge of the loop _A''_. For the average workman, polishing the flat parts _m_ is the most difficult to do, and for this reason we will give entire details. It is to be expected that the regulator bar will spring a little in hardening, but if only a little we need pay no attention to it.

[Ill.u.s.tration: Fig. 44]

[Ill.u.s.tration: Fig. 45]

[Ill.u.s.tration: Fig. 46]