Chapter XIV: Plates, Pivots and Time Trains (3)

TO CALCULATE CLOCK TRAINS.—Britten gives the following rule: Divide the number of pendulum vibrations per hour by twice the number of escape wheel teeth; the quotient will be the number of turns of escape wheel per hour. Multiply this quotient by the number of escape pinion teeth, and divide the product by the number of third wheel. This quotient will be the number of times the teeth of third wheel pinion must be contained in center wheel.

Clock Trains and Lengths of Pendulums.

===========+=========+========+==============+==========
| | | Vibrations | Length of
| | Escape | of Pendulum | Pendulum
Wheels | Pinions | Wheel | —Min. | in Inches
-----------+---------+--------+--------------+----------
120 90 75| 10 10 9| Double | *30 | 156.56
| |3 legged| |
120 90 90| 10 9 9 | Do. | *40 | 88.07
128 120| 16 | 30 | 60 | 39.14
112 105| 14 | 30 | 60 | 39.14
96 90| 12 | 30 | 60 | 39.14
80 75| 10 | 30 | 60 | 39.14
64 60| 8 | 30 | 60 | 39.14
68 64| 8 | 30 | 68 | 30.49
70 64| 8 | 30 | 70 | 28.75
72 64| 8 | 30 | 72 | 27.17
75 60| 8 | 32 | 75 | 25.05
72 65| 8 | 32 | 78 | 23.15
75 64| 8 | 32 | 80 | 22.01
84 64| 8 | 30 | 84 | 19.97
86 64| 8 | 30 | 86 | 19.06
88 64| 8 | 30 | 88 | 18.19
84 78| 7 | 20 | 89.1 | 17.72
80 72| 8 | 30 | 90 | 17.39
84 78| 7 | 21 | 93.6 | 16.08
94 64| 8 | 30 | 94 | 15.94
84 78| 8 | 28 | 95.5 | 15.45
108 100| 12 & 10 | 32 | 96 | 15.28
84 84| 9 & 8 | 30 | 98 | 14.66
84 78| 7 | 22 | 98 | 14.66
84 78| 8 | 29 | 98.9 | 14.41
80 80| 8 | 30 | 100 | 14.09
85 72| 8 | 32 | 102 | 13.54
84 78| 8 | 30 | 102.4 | 13.44
84 78| 7 | 23 | 102.5 | 13.4
105 100| 10 | 30 | 105 | 12.78
84 78| 8 | 31 | 105.8 | 12.59
84 78| 7 | 24 | 107 | 12.3
96 72| 8 | 30 | 108 | 12.08
84 78| 8 | 32 | 109.2 | 11.82
88 80| 8 | 30 | 110 | 11.64
84 77| 7 | 25 | 110 | 11.64
84 78| 7 | 25 | 111.4 | 11.35
84 80| 8 | 32 | 112 | 11.22
84 78| 8 | 33 | 112.6 | 11.11
96 76| 8 | 30 | 114 | 10.82
115 100| 10 | 30 | 115 | 10.65
84 78| 7 | 26 | 115.9 | 10.49
96 80| 8 | 30 | 120 | 9.78
84 70| 7 | 30 | 120 | 9.78
84 78| 7 | 27 | 120.3 | 9.73
90 84| 8 | 31 | 122 | 9.46
84 78| 7 | 28 | 124.8 | 9.02
100 80| 8 | 30 | 125 | 9.01
90 84| 8 | 32 | 126 | 8.87
100 96| 10 | 40 | 128 | 8.59
84 78| 7 | 29 | 129.3 | 8.42
100 78| 8 | 32 | 130 | 8.34
84 77| 7 | 30 | 132 | 8.08
84 78| 7 | 30 | 133.7 | 7.9
90 90| 8 | 32 | 135 | 7.73
84 78| 7 | 31 | 138.2 | 7.38
84 80| 8 | 40 | 140 | 7.18
120 71| 8 | 32 | 142 | 6.99
84 78| 7 | 32 | 142.6 | 6.93
100 87| 8 | 32 | 145 | 6.69
84 78| 7 | 33 | 147.1 | 6.5
100 96| 8 | 30 | 150 | 6.26
84 78| 7 | 34 | 151.6 | 6.1
96 95| 8 | 32 | 152 | 6.09
84 77| 7 | 35 | 154 | 5.94
104 96| 8 | 30 | 156 | 5.78
84 78| 7 | 35 | 156 | 5.78
120 96| 9 & 8 | 30 | 160 | 5.5
84 78| 7 | 36 | 160.5 | 5.47
84 78| 7 | 37 | 164.9 | 5.15
132 100| 9 & 8 | 27 | 165 | 5.17
84 78| 7 | 38 | 169.4 | 4.88
128 102| 8 | 25 | 170 | 4.87
84 78| 7 | 39 | 173.8 | 4.65
36 36 35| 6 | 25 | 175 | 4.6
84 77| 7 | 40 | 176 | 4.55
84 78| 7 | 40 | 178.3 | 4.43
45 36 36| 6 | 20 | 180 | 4.35
47 36 36| 6 | 20 | 188 | 3.99
===========+=========+========+==============+==========

* These are good examples of turret clock trains; the great
wheel (120 teeth) makes in both instances a rotation in
three hours. From this wheel the hands are to be driven.
This may be done by means of a pinion of 40 gearing with
the great wheel, or a pair of bevel wheels bearing the
same proportion to each other (three to one) may be used,
the larger one being fixed to the great wheel arbor. The
arrangement would in each case depend upon the number and
position of the dials. The double three-legged gravity
escape wheel moves through 60° at each beat, and therefore
to apply the rule given for calculating clock trains it must
be treated as an escape wheel of three teeth.

Take a pendulum vibrating 5,400 times an hour, escape wheel of 30, pinions of 8, and third wheel of 72. Then 5,400 ÷ 60 = 90. And 90 × 8 ÷ 72 = 10. That is, the center wheel must have ten times as many teeth as the third wheel pinion, or ten times 8 = 80.

The center pinion and great wheel need not be considered in connection with the rest of the train, but only in relation to the fall of the weight, or turns of mainspring, as the case may be. Divide the fall of the weight (or twice the fall, if double cord and pulley are used) by the circumference of the barrel (taken at the center of the cord); the quotient will be the number of turns the barrel must make. Take this number as a divisor, and the number of turns made by the center wheel during the period from winding to winding as the dividend; the quotient will be the number of times the center pinion must be contained in the great wheel. Or if the numbers of the great wheel and center pinion and the fall of the weight are fixed, to find the circumference of the barrel, divide the number of turns of the center wheel by the proportion between the center pinion and the great wheel; take the quotient obtained as a divisor, and the fall of the weight as a dividend (or twice the fall if the pulley is used), and the quotient will be the circumference of the barrel. To take an ordinary regulator or 8-day clock as an example—192 (number of turns of center pinion in 8 days) ÷ 12 (proportion between center pinion and barrel wheel) = 16 (number of turns of barrel). Then if the fall of the cord = 40 inches, 40 × 2 ÷ 16 = 5, which would be circumference of barrel at the center of the cord.

If the numbers of the wheels are given, the vibrations per hour of the pendulum may be obtained by dividing the product of the wheel teeth multiplied together by the product of the pinions multiplied together, and dividing the quotient by twice the number of escape wheel teeth.

The numbers generally used by clock makers for clocks with less than half-second pendulum are center wheel 84, gearing with a pinion of 7; third wheel 78, gearing with a pinion of 7.

The product obtained by multiplying together the center and third wheels = 84 × 78 = 6,552. The two pinions multiplied together = 7 × 7 = 49. Then 6,552 ÷ 49 = 133.7. So that for every turn of the center wheel the escape pinion turns 133.7 times. Or 133.7 ÷ 60 = 2.229, which is the number of turns in a minute of the escape pinion.

The length of the pendulum, and therefore the number of escape wheel teeth, in clocks of this class is generally decided with reference to the room to be had in the clock case, with this restriction, the escape wheel should not have less than 20 nor more than 40 teeth, or the performance will not be satisfactory. The length of the pendulum for all escape wheels within this limit is given in the preceding table. The length there stated is of course the theoretical length, and the ready rule adopted by clockmakers is to measure from the center arbor to the bottom of the inside of the case, in order to ascertain the greatest length of pendulum which can be used. For instance, if from the center arbor to the bottom of the case is 10 inches, they would decide to use a 10-inch pendulum, and cut the escape wheel accordingly with the number of teeth required as shown in the table. But they would make the pendulum rod of such a length as just to clear the bottom of the case when the pendulum was fixed in the clock.

In the clocks just referred to the barrel or first wheel has 96 teeth, and gears with a pinion of eight.

Month clocks have an intermediate wheel and pinion between the great and center wheels. This extra wheel and pinion must have a proportion to each other of 4 to 1 to enable the 8-day clock to go 32 days from winding to winding. The weight will have to be four times as heavy, plus the extra friction, or if the same weight is used there must be a proportionately longer fall.

Six-months clock have two extra wheels and pinions between the great and center wheels, one pair having a proportion of 4½ to 1 and the other of 6 to 1. But there is an enormous amount of extra friction generated in these clocks, and they are not to be recommended.

The pivot holes and all the other holes in the frames, are punched at one operation after the frames have been blanked and flattened. They are placed in the press, and a large die having punches in it of the proper size and in the right position for the holes, comes down on the frame and makes the holes with great rapidity and accuracy. These holes are finished afterwards by a broach. In some kinds of clocks, where some of the pivot holes are very small, the small holes are simply marked with a sharp point in the die, and afterwards drilled by small vertical drills. These machines are very convenient for boring a number of holes rapidly. The drill is rotated with great speed, and a jig or plate on which the work rests is moved upwards towards the drill by a movement of the operator’s foot. All the boring, countersinking, etc., in American clocks, is done through the agency of these drills. Bending the small wires for the locking work, the pendulum ball, etc., is rapidly effected by forming. As no objectionable marks have been made on the surface of either the thick or smaller wires during any process of construction, all that is necessary to finish the iron work is simply to clean it well, which is done in a very effective manner by placing a quantity of work in a revolving tumbling box, which is simply a barrel containing a quantity of sawdust.

Milling the winding squares on barrel arbors is an ingenious operation. The machine for milling squares and similar work is made on the principle of a wheel cutting engine. The work is held in a frame, attached to which is a small index plate, like that of a cutting engine. In the machine two large mills or cutters, with teeth in them like a file, are running, and the part to be squared is moved in between the revolving cutters, which operation immediately forms two sides of the square. The work is then drawn back, and the index turned round, and in a like manner the other two sides of the square are formed. The cutting sides of the mills are a little bevelled, so that they will produce a slight taper on the squares.

Winding keys have shown great improvements. Some manufacturers originally used cast iron ones, but the squares were never good in them, and brass ones were adopted. At first the squares were made by first drilling a hole and driving a square punch in with a hammer; and to make the squares in eighteen hundred keys by this method was considered a good day’s work. Restless Yankee ingenuity, however, has contrived a device by which twenty or twenty-five thousand squares can be made in a day, while at the same time they are better and straighter squares than those by the old method; but we are not at liberty to describe the process at present, but only to state that it is done by what machinists call drilling a square hole.

Pendulum rods are made from soft iron wire, and the springs on the ends rolled out by rollers. Two operations are necessary. The first roughs the spring out on rollers of eccentric shape, and the spring is afterwards finished on plain smooth rollers. The pendulum balls in the best clocks are made of lead, on account of its weight, and cast in an iron mold in the same manner as lead bullets, at the rate of about eighteen hundred a day. A movable mandrel is placed in the mold to produce the hole that is in the center of the ball. The balls are afterwards covered with a shell of brass, polished with a bloodstone burnisher. The various cocks used in these clocks are all struck up from sheet brass, and the pins in the wheels in the striking part are all swedged into their shape from plain wire. The hands are die struck out of sheet steel, and afterwards polished on emery belts, and blued in a furnace.

All the little pieces of these clocks are riveted together by hand, and the different parts of the movement, when complete, are put together by workmen continually employed in that department. Although the greatest vigilance is used in constructing the different parts to see that they are perfect, when they come to be put together they are subjected to another examination, and after the movements are put in the case the clocks are put to the test by actual trial before they are packed ready for the market. As a general rule, all the different operations are done by workmen employed only at one particular branch; and in the largest factories from thirty to fifty thousand clocks of all classes may be seen in the various stages of construction.

Such is a description of the main points in which the manufacture of American clock movements differs from those manufactured by other systems. All admit that these clocks perform the duties for which they are designed in an admirable manner, while they require but little care to manage, and when out of order but little skill is necessary to repair them. Of late years there has been a growing demand for ornamental mantel-piece clocks in metallic cases of superior quality, and large numbers of these cases of both bronze and gold finish are being manufactured, which, for beauty of design and fine execution, in many instances rival those of French production. The shapes of the ordinary American movements were, however, unsuitable for some patterns of the highest class of cases, and the full plate, round movements of the same size as the French, but with improvements in them that in some respects render them more simple than the French, are now manufactured. Exactly the same system is employed in the manufacture of the different parts of these clocks that is practiced in making the ordinary American movements.