The Modern Clock / A Study of Time Keeping Mechanism; Its Construction, Regulation and Repair

by Ward L. Goodrich

It occasionally happens in mantel clocks that the pendulum when brought to time is just too long for the case when too thick a spring is used. In such a case thinning the spring will require the bob to be raised a little and also give a better motion. If compelled to make a spring use a piece of mainspring about .007 thick and ⅜ wide for small pendulums and the same spring doubled for heavier pendulums, making the acting part of the spring about 1.5 inches long.

The suspension spring for a rather heavy pendulum is better divided, that is, two springs, held by two sets of clamps, and jointly acting as one spring. The length will be the same as to the acting part, and that part held at each end by the clamps may be ¾ inch long; total length, 1.5 inches with ⅜ inch at each end held in the clamps. These clamps are best soldered on to the spring with very low flowing solder so as not to draw the temper of the spring, and then two rivets put through the whole, near the lower edge of the clamps. The object of securing the clamps so firmly is so that the spring may not bend beyond the edge of the clamps, as if this should take place the clock will be thrown off of its rate. After a time the rate would settle and become steady, but it only causes an extra period of regulating that does not occur when the clamps hold the spring immovable at this point. About in the center of each of the clamps, when soldered and riveted, is to be a hole bored for a pin, which pins the clamp into the bracket and holds the weight of the pendulum.

The width of this compound spring for a seconds’ pendulum of average weight may be .60 inch, from outside to outside, each spring .15 inch wide. This will separate the springs .30 inch in the center. With this form of spring, the lower end of each spring being held in a pair of clamps, the clamps will have to be let into the top of the rod, and held in by a stout pin, or the pendulum finished with a hook which will fit the clamp. In letting the clamp into the rod, the clamp should just go into the mortise and be without side shake, but tilt each way from the center a little on the pin, so that when the pendulum is hung it may hang perpendicular, directly in the center of both springs. Also, the top pair of clamps should fit into a bracket without shake, and tilt a little on a pin, the same as the lower clamps. These two points, each moving a little, helps to take any side twist away, and allows the whole mechanism to swing in line with the center of gravity of the mass from end to end. With the parts well made, as described, the bob will swing in a straight line from side to side, and its path will be without any other motion except the one of slight curvature, due to being suspended by a fixed point at the upper clamp.

Pendulum Supports.—Stability in the movement and in the suspension of the pendulum is very necessary in all forms of clocks for accurate timekeeping. The pendulum should be hung on a bracket attached to the back of the case ([see Fig. 6]), and not be subject to disturbance when the movement is cleaned. Also the movement should rest on two brackets attached to the bracket holding the pendulum and the whole be very firmly secured to the back board of the case. Screws should go through the foot pieces of the brackets and into a stone or brick wall and be very firmly held against the wall just back of the brackets. Any instability in this part of a clock is very productive of poor rates. The bracket, to be in its best form, is made of cast iron, with a large foot carrying all three separate brackets, well screwed to a strong back board and the whole secured to the masonry by bolts. Too much firmness cannot be attained, as a lack of it is a very great fault, and many a good clock is a very poor timekeeper, due to a lack of firmness in its supports and fastenings. The late Edward Howard used to make his astronomical clocks with a heavy cast iron back, to which the rest of the case was screwed, so that the pendulum should not swing the case. Any external influence that vibrates a wall or foundation on which a clock is placed, is a disturbing influence, but an instability in a clock’s attachment to such supports is a greater one. Many pendulums swing the case in which they hang (from unstable setting up) and never get down to or maintain a satisfactory rate from that cause. This is also aggravated by the habit of placing grandfather clocks on stair landings or other places subject to jarring. The writer knows of several clocks which, after being cleaned, kept stopping until raised off the floor and bolted to the wall, when they at once took an excellent rate. The appearance of resting on the floor may be preserved, if desirable, by raising the clock only half an inch or so, just enough to free it from the floor.

Crutches.—The impulse is transmitted to the pendulum from the pallet staff by means of a wire, or slender rod, fastened at its upper end to the pallet staff and having its lower end terminating in a fork (crutch), loop, or bent at right angles so as to work freely in a slot in the rod. It is also called the verge wire, owing to the fact that older writers and many of the older workmen called the pallet fork the verge, thus continuing the older nomenclature, although of necessity the verge disappeared when the crown wheel was discarded.

In order to avoid friction at this very important point, the centers of both axes of oscillation, that of the pallet arbor and that of the pendulum spring, where it bends, should be in a straight horizontal line. If, for instance, the center of suspension of the pendulum be higher, then the fork and the pendulum describe two different arcs of circles; that of the pendulum will be greater than that of the fork at their meeting point. If, however, the center of suspension of the pendulum be lower than that of the fork, they will also describe two different arcs, and that of the pendulum will be smaller than that of the fork at their point of meeting. This, as can be readily understood, will cause friction in the fork, the pendulum going up and down in it. This is prevented when, as stated before, the center of suspension of the pendulum is in the prolonged straight imaginary line going through the center of the pivots of the fork, which will cause the arcs described by the fork and the pendulum to be the same. It will be well understood from the foregoing that the pendulum should neither be suspended higher nor lower, nor to the left, nor to the right of the fork.

If the centers of motion do not coincide, as is often the case with cheap clocks with recoil escapements, any roughness of the pendulum rod where it slides on the crutch will stop the clock, and repairers should always see to it that this point is made as smooth as possible and be very slightly oiled when setting up. If putting in a new verge wire, the workman can always tell where to bend it to form the loop by noticing where the rod is worn and forming the loop so that it will reach the center of that old crutch or loop mark on the pendulum rod. If the verge wire is too long, it will give too great an arc to the pendulum if the latter is hung below the pallet arbor, as is generally the case with recoil escapements of the cheap clocks, and if it is too short there will not be sufficient power applied to the pendulum when the clock gets dirty and the oil dries, in which case the clock will stop before the spring runs down.

An important thing to look after when repairing is in the verge wire and loop (the slot the pendulum rod goes through). After the clock is set up and oiled, put it on a level shelf; have a special adjusted shelf for this level adjusting, one that is absolutely correct. Have the dial off. If the beat is off on one side, so that it bangs up heavily on one side of the escape wheel, bend the verge wire the same way. That will reverse the action and put it in beat. So far so good—but don’t stop now. Just notice whether if that shelf were tipped forward or back, as perhaps your customer’s may, that the pendulum should still hang plumb and free. Now if the top of your clock tips forward, the pendulum ball inclines to hang out toward the front. We will suppose you put two small wedges under the back of the case. Now notice in its hanging out whether the pendulum rod pinches or bears in the throat of the verge; or if it tips back, see if the rod hits the other end of the slot. This verge slot should be long enough, with the rod hanging in the middle when adjusted to beat on a level, to admit of the clock pitching forward or back a little without creating a friction on the ends of the slot. This little loop should be open just enough to be nice and free; if open too much, you will notice the pallet fork will make a little jump when carrying the ball over by hand. This is lost motion. If this little bend of wire is not parallel it may be opened enough inside, but if pitched forward a little it will bind in the narrowest part of the V and then the clock will stop. The clock beat and the tipping out or in of the clock case, causing a binding or bearing of the pendulum rod in this verge throat, does more towards stopping clocks just repaired than all other causes.

Putting in Beat.—To put a clock in beat, hang the clock in such a position that when the pendulum is at rest one tooth of the escape wheel will rest on the center of a pallet stone. Screwed on the case of the clock at the bottom of the pendulum there is, or should be, an index marked with degrees. Now, while the escape wheel tooth is resting on the pallet, as explained above, the index of the pendulum should point to zero on the index. Move the pendulum until the tooth just escapes and note how many degrees beyond zero the pendulum point is. Say it escapes 2° to the left; now move the pendulum until the next tooth escapes—it should escape 2° to the right. But let us suppose it does not escape until the index of the pendulum registers 5° to the right of zero. In this case the rod attached to the pallets must be bent until the escape wheel teeth escape when the pendulum is moved an even number of degrees to the right and left of zero, when the clock will be in beat.

Close Rating with Shot.—Very close rating of a seconds’ pendulum, accompanied by records in the book, may be got with the nut alone, but there is the inconvenience of stopping the clock to make an alteration. This may be avoided by having a small cup the size of a thimble or small pill box on the pendulum top. This can be lifted off and put back without disturbing the motion of the pendulum. In using it a number of small shot, selected of equal size, are put in, say 60, and the clock brought as nearly as possible to time by the nut. After a few days the cup may be emptied and put back, when on further trial the value of the 60 shot in seconds a day will be found. This value divided by 60 will give the value of a single shot, by knowing which very small alterations of rate may be made with a definite approach towards accuracy, and in much less time than by putting in or taking out one or more shot at random.