Pivot point

“ 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 [Pg 24] 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. ”

“ Pivots of maneuver are detachments of troops left to guard points which it is essential to hold, while the bulk of the army proceeds to the fulfillment of some important end; and when this is accomplished the pivot of maneuver ceases to exist. Thus, Ney's corps was the pivot of Napoleon's maneuver by Donauwerth and Augsburg to cut Mack from his line of retreat. A pivot of operations, on the contrary, is a material point of both strategical and tactical importance, serves as a point of support and endures throughout a campaign. ”

“ Wheel made to the reverse flank. When [744] the change is made to the REVERSE hand, the pivot leader having arrived as before, at the spot where he gives his word right or left quarter wheel! for each man to give a small turn of his horse’s head FROM the pivot hand, will begin in his own person to circle BEHIND the line from the old, so as to enter the new direction twenty or thirty yards from the point of intersection, which, in this case, he leaves at some small distance WITHOUT his pivot hand. ”

“ The left pivot man of each company faces at this cautionary word, and remains a fixed point, on which the rest wheel back when they receive directions so to do. When the column of companies is to be wheeled into line, the word on is equally understood to direct the moveable parts of each company towards the given pivot which faces, and remains a fixed point. In the British drill instructions, they say, to the left wheel into line; but in the third part of the regulations to is wholly omitted, and the commanding officer [494] uses the term left wheel into line, and vice versa ”

“ By simply pressing on this mechanicismmechanicism, the latter checks the motion of the wheel by application of friction at the pivot, and brings it to a standstill at any point which he may desire.
Not always, however, is the proprietor of the wheel the only sharper on the ground. Sometimes he discovers, when it is too late, that he has been playing a game of “diamond cut diamond.” ”

“ It is understood, of course, that the couples have no components (in the generalized sense) except of the types indicated; for instance, they may consist in each case of a force applied to the top at a point of the axis, and of the accompanying reaction at the pivot. ”

“ The point of pivot motion is the point of contact between wheel and floor. Such pucker and wear carpets and are sluggish in their swiveling action. Two rollers side by side will, in swiveling, turn in opposite directions, and it will be found that they roll upon the floor, instead of pivoting, as does the single wheel; but, if the floor should be irregular, as is often the case, one wheel of the pair would not touch the floor, and the two-wheeled caster would become practically a one-wheeled caster. ”

“ The hole for the pivot should be bored 2 inches deep and be placed well forward of the centre. To make the vane balance, the rear portion from the pivot to the stern should be planed thin and rounded with the spokeshave.
Fig. 100. A six-bladed mill
At the stern should be a small two-bladed pro [166] peller, pivoted on a flat-head wire nail. If the stern is still too heavy, the balance can be restored by driving into the forward point a round-headed screw, or by attaching another small propeller. ”

“ The tool t, is operated laterally to increase or diminish the rate of feed by the screw e, which also serves as a pivot, so that by operating the thumb-screw f, the tool point may be adjusted for distance from the centre of the bore d, or in other words the diameter to which the tool t will turn the work is adjusted by the thumb-screw f. g is the head of the pivot screw that the swing tool holder h works upon, and this swing motion carries the forming tool or cutter x, which shapes the work to the required form. ”

“ 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 illustrated 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. ”

“ The turning up of a new pivot does not differ in any way from the instructions given for turning pivots on a new staff. With a little care both in turning and finishing, a new pivot can be put in so nicely that only the initiated can tell it, and then only with the aid of a strong glass. ”

“ Good pivoting is an art in itself, and although there are many who undertake to do this work, there are but few who can pivot a staff in such a manner that it will bear close inspection under the glass. We often hear watchmakers brag of the secrets they possess for hardening pivot drills, but I fancy they would be somewhat surprised if they traveled around a little, to find how many watchmakers harden their drills in exactly the same way that they do. ”

“ Don’t you see the left hand is the pivot: if you hold it out as far as you can, then the Long part of the rod is your side of the pivot, and the short little piece is beyond it—then you’ve only got to move that little piece. If you shoot in our old way then the long piece is the other side of the pivot, and of course the least motion makes such a difference. ”

“ I consider it well for young workmen to practice pivot setting in some old and useless watch any spare time they may have, and thus become adepts at this work. Unhindered, I am not over on an average of one-half hour in setting any ordinary pivot, especially if I do not have to cement my work. If this is a balance pivot, be very careful to see that your balance is true and poised before putting on hairspring and roller. ”

“ For pivots band b and e may use brass screws and small pieces of hard wood as nuts to hold them in position. The nuts should screw on rather stiffly, and not be forced hard against the rods, as free motion with little friction at all joints is essential for good work.
[Illustration: FIG. 187.—Diagram showing how to mark off pantograph rods. The dotted lines above rod give distances of holes from ends.]
The fixed pivot at a may be merely the shank of a wire nail of the proper size driven into the board, a cork collar being slipped over it to keep the rod the proper distance from the board. ”

“ Pit′yroid, bran-like. [Gr. pityron, bran.]
Più, pū, adv. more.—Più allegro, quicker. [It.]
Pivot, piv′ut, n. the pin on which anything turns: the officer or soldier at the flank upon whom a company wheels: that on which anything depends or turns.—adj. Piv′otal, of the nature of a pivot: acting as a pivot.—n. Piv′ot-bridge, a form of swing-bridge moving on a vertical pivot.—adj. Piv′oted, furnished with a pivot or pivots.—ns. Piv′ot-gear′ing, a system of gearing permitting the driving-shaft to be swivelled so as to set the machine in any direction with relation to the power ”

“ 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. ”

“ Friction of Pivots and Collars.—When a shaft is acted upon by a force tending to shift it lengthways, that force must be balanced by the reaction of a bearing against a pivot at the end of the shaft; or, if that be impossible, against one or more collars, or rings projecting from the body of the shaft. The bearing of the pivot is called a step or footstep. Pivots require great hardness, and are usually made of steel. The flat pivot is a cylinder of steel having a plane circular end as a rubbing surface. Let N be the total pressure sustained by a flat pivot of the radius r ”

“ Wheels are made on a Halted pivot from Line into Column, and from Column into Line. The principle of the Moveable pivot must always be applied to the wheel of divisions marching in column. Wheels of divisions may be either made forward, or backward. In progressive movements they are to be made Forward, but particular occasions require that they should be made Backward on the pivot flank. ”

“ 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. ”

“ I am inclined to believe, therefore, that the pivot-press may be used with excellent effect in many instances, especially from its simplicity and ease of construction, when a sudden need arises for the accommodation of a new accession of books. I may further draw attention to a special merit—its singular lightness even when full of volumes. A child can work it with ease, unlike the sliding-press, which, when quite full, may tax the strength of a powerful man. ”

“ Run a hole vertically through C and the baseboard for the pivot, which should be 4-1/2 inches long, so as to project 1 inch when driven right home. Take some trouble over getting the holes in L and C quite square to the baseboard, as any inaccuracy will make the lever twist as it moves. To prevent the pivot cutting into the wood, screw to the top of C a brass plate bored to fit the pivot accurately. The strain will then be shared by the screws.
The horns of A should be long enough to allow the outside of the fixed grip to be 2-1/4 inches from the inside of the handle. ”

“ Using one foot for a pivot, he keeps moving round by the aid of the other, so as make about ten revolutions in a minute, and, while in motion, successively takes the eggs from the basket, and, with his right hand only, puts each into a loop, drawing it tight, so as to retain the egg firmly in an equipoised state. ”

“ The acid simply rusts the pivot and the hole, but I cannot see that this will hold it any more firmly in place while finishing. If the taper is a gradual one and the pivot a good close fit, there will be little danger of it loosening while dressing to shape. If too great a taper is given to the plug, there is danger of splitting the end of the staff, and this involves the making of an entire new staff. ”

“ The upper pivot, or bearing is made of tempered steel wire and of sufficiently small diameter to be quite flexible in the length between the top of the brass shaft and the guide ring in which it rotates. ”

“ If [Pg 42] your drill is made from a piece of Stubb's steel wire, or an old French or Swiss graver, you not only know that the material in it is first-class, but you can leave the base of the drill solid and substantial, with enough metal in it to resist considerable pressure. The part of the drill which actually enters the pivot is very short, and the end can be turned down to the desired diameter. Turn or reduce your wire by means of a pivot file so as to be smooth and conical, as shown at A, Fig. ”

“ I have assumed 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. ”

“ It appears that the rapidity with which a rubbing surface wears away is proportional to the friction and to the velocity jointly, or nearly so. Hence the pivots already mentioned wear unequally at different points, and tend to alter their figures. Schiele has invented a pivot which preserves its original figure by wearing equally at all points in a direction parallel to its axis. ”

“ One member of each team takes a position on the distance line, opposite to and facing his team. At the signal to go the first man on each team runs forward, locks his right arm in the right arm of the man on the distance line and in this position spins twice around, using the man on the distance line as a pivot. Completing his second spin, he remains on the distance line while the man who was there returns and tags off the next member of his team, who repeats the performance. The race ends when the last man to spin around the pivot crosses the base line. ”

“ There are two ways in which a body may be conceived to be moveable around an axis. 1. By having pivots at two points which rest in sockets, so that when the body is moved it must revolve round the right line joining the pivots as an axis. 2. A thin cylindrical rod may pass through the body, on which it may turn in the same manner as a wheel upon its axle.
If the force be applied to the body in the direction of133 the axis, it is evident that no motion can ensue, and the effect produced will be a pressure on that pivot towards which the force is directed. ”