Screwdriver

“ If the corners break they can be reground, but care should be taken not to make the angle too obtuse or the driver will slip out of the slot in the screw-head. The bevel should have a long taper. A shop should be equipped with different sizes of screwdrivers to fit the different sizes of screws. Screwdrivers vary in size, the shank ranging in length from 21⁄2" to 18". A long screwdriver is more powerful than a short one, for the [page 105] screwdriver is rarely exactly in line with the axis of the screw, but the handle revolves in a circle. ”

“ A round-handled screwdriver is not so satisfactory as one with an elliptical or polygonal handle, as it is impossible to obtain as good a grip upon the former as upon the latter; a round handle, planed flat upon the two opposite sides, is quite commonly used.
(C.) Ratchet screwdrivers are useful in many places where it is difficult to use two hands, and there are patent quick-action screwdrivers on the market which are suitable only for certain kinds of light work, as what is gained in speed is lost in power. ”

“ Take an ordinary round paintbrush and cut the handle off, leaving it about 1-1/2 in. long, then saw a V-shaped notch in it, as shown in Fig. 1. Attach the brush to the ratchet screwdriver, Fig. 2, by inserting the screwdriver blade in the notch of the brush handle, and secure it by wrapping a strong cord around the handle. Place the brush in the tuft and work the screwdriver handle, as in turning a screw. A few quick turns of the brush will throw out the dirt which is impossible to remove with a straight brush. ”

“ In taking down a lock the beginner should work slowly and cautiously, thinking in every case before acting. His screwdriver should be pressed well-down in the notch of every screw to prevent damage to the head, and if he apprehends the slightest danger of getting “things mixed,” he should lay each screw and its piece in different places upon his bench. Of course, there will be no such necessity after a few locks have been taken down, but such a necessity might exist at the very beginning; at least there is no harm to grow out of taking what is known to be the safe side in every case. ”

“ When the shank is broken off close to the butt, the same treatment will sometimes answer, but the strain here is so much greater that it is sometimes necessary to put in a new shank. In fact, it is always better to do so.
2. Flanges, damper heads, and all small wooden parts are liable to break or come unglued. The watchmaker's screwdriver, the binding wire and the glue must always be at hand for these emergencies. These breaks are generally in places where [Pg 064] wrapping is not permissible, and you are compelled to drill. Keep the screwdriver well sharpened and the drilling is easy. ”

“ When the gimlet was through the door, I selected a tool on whose use I had often speculated—a sharp-edged spike, like a diminutive and very stumpy bayonet—which I proceeded to use broach-wise to enlarge the hole. When this tool worked loose, I exchanged it for the screwdriver, with which I managed to broach the hole out to about half an inch in width. And this was as large as I could make it, and it was not large enough. True, one could breathe fairly comfortably through a half-inch hole, but, with the deadly gas circulating around, a freer opening was very desirable. ”

“ Then set the cylinder adjusting screw, and insert the wooden screws in lock face and drive them home with the screwdriver. Hold and adjust the escutcheon so that the knob will rotate back and forth automatically without friction, starting the screw holes with an awl. If the doors are made of hardwood, an automatic drill will have to be used to bore the screw holes. In such a case, follow the directions just given regarding escutcheons ”

“ This means an increased leverage, so that the longer the screwdriver, the greater the leverage.
For heavy work, screwdriver-bits, Fig. 189, in a bit-stock are useful, and for quick work, the spiral screwdriver, Fig. 190, and for small work, the ratchet-screwdriver.
7. MEASURING AND MARKING TOOLS.
It is a long step from the time when one inch meant the width of the thumb, and one foot meant the length of the foot, to the measuring of distances and of angles which vary almost infinitesimally. ”

“ Screwdrivers.—These are tools of impulsion, and at least two or three will be required—long and short, and with wide and narrow blade. For general work, a tool of medium length should be obtained, although there are, on the one hand, enthusiastic advocates of a short tool, and on the other hand of a long tool for each and every purpose. Any advantage gained by a short over a long tool, or the reverse, is one of advantage in special circumstances only, and not one of saved energy; theoretically,
Fig. ”

“ A closely related phenomenon, with a slightly different intent, is the habit manufacturers have of inventing new screw heads so that only Designated Persons, possessing the magic screwdrivers, can remove covers and make repairs or install options. ”

“ The Screw-driver.—It has been said that the feminine mind cannot grasp the difference between a screw-driver, a cork-screw, and a gimlet, and it remains with you to prove the contrary. A poor screw-driver is one of the most exasperating 7of poor tools, and a trial to one’s patience and temper; besides, it is of little use attempting to “make it do,” for it seldom will do. The edge is usually shaped like Fig. 2, and it slides and slips out of the groove of the screw until it has turned and worn down its edges and made the screw useless. Fig. 3 shows the proper shape for a screw-driver. ”

“ If the mechanic desires to make these himself, select octagon steel, about one-quarter inch diameter, draw one end to form the tang, and the other to form the screw-driving part. Get good apple, beech or maple wood handles. Let the length project about six or seven inches from the handle. For the larger size screw-drivers get steel three-eighths diameter. Old files, with the temper drawn and the points ground to shape, make a passable screw-driver. Screw-drivers purchased at the store, are generally not so satisfactory as those made from rods. ”

“ The ordinary screw, cut by dies or in the screw-cutting lathe, is found, on applying comparatively coarse tests, to be far from accurate in pitch, while the thread may be wavy or “ drunken " and the diameter may not be uniform at all points. There are several methods of correcting the errors in screws; the principal one is that of retarding or accelerating the traverse motion of the screw-cutting tool by means of a compensating lever bearing on a compensating bar, which is formed after observations have been made on the degree of accuracy of the leading screw used to propel the tool carriage. ”

“ The lead screw for screw cutting is placed in a trough running inside the lathe bed, so that it is nearer to the cutting tool than if placed outside that bed, while it is entirely protected from the lathe cuttings and from dirt or dust; and the feed-driving mechanism is so arranged that both may be in gear with the live spindle, and either the rod feed or screw-cutting feed may be put into action instantly, while putting one into action throws the other out, and thus avoid the breakage that occurs when both may be put into action at the same time. ”

“ We now come to the most difficult operation in turning, that of cutting a screw; to perform it well and easily is a proof of the workman’s skill and proficiency in the art. There are many ways of doing it; we shall therefore give the best and least expensive. The screw tools, figures 14 and 15, plate 1, must fit exactly one into the other. Fig. 15 is an outside, Fig. 14 an inside tool. As the threads may be required to be cut coarse or fine, according to the work you are engaged upon, the small grooves in the tools are made to suit. ”

“ The screw is a spiral thread or groove cut round a cylinder, and everywhere making the same angle with the length of it. The force of a power applied to turn a screw round is to the force with which it [297] presses upward, or downward, setting aside the friction, as the distance between two threads is to the circumference where the power is applied; or the advantage gained is as much as the circumference of a circle described by the handle of the winch exceeds the interval, or distance, between the spirals of the screw. Hence the force of any machine turned by a screw can readily be computed ”

“ Another step in the direction of economy depends on the removal of all screw-cutting, except those screws which are of several feet in length, from the ordinary lathe to the special chasing and screwing machines. The screw-cutting arrangement of an engineer's lathe is a cumbrous apparatus to fit up and set in motion for the cutting of screws of small dimensions. When there was no other method available except that of common dies operated by hand or carried in a screwing machine, there was good reason why a true cutting tool should be operated in the lathe through change wheels. ”

“ The third method, screwing, has come into extensive use since the standard screwing machine was introduced in America by the McKay Sewing-Machine Association, of Boston, Massachusetts, and in Europe by the Blake and Goodyear Company, of London. The standard screw machine, which is an American invention, though the idea was anticipated by a Frenchman named Blanchon in 1856, is provided with a reel of stout screw-threaded brass wire, which by the revolution of the reel is inserted into and screwed through outsole, upper edge and insole. ”

“ The Screw-driver is used to drive in and take out screws. It ought to have a very hard tough edge and a long handle. When placed in the head of the screw, to drive in, it should be turned from left to right, and [Pg 120] in taking out, from right to left. There is a particular way of getting out a screw, which is only to be learned by a little practice. ”

“ To make the teeth of a pair of endless screws fit correctly and work smoothly, a hardened steel screw is made of the figure of the smaller screw, with its thread or threads notched so as to form a cutting tool; the larger screw, or “wheel,” is cast approximately of the required figure; the larger screw and the steel screw are fitted up in their proper relative position, and made to rotate in contact with each other by turning the steel screw, which cuts the threads of the larger screw to their true figure. ”

“ The screw A is the most essential part of the tool, and its construction requires great accuracy. Its diameter is 1⁄2 inch, and it is cut with 20 threads per inch. In the upper end of the screw is driven the ball H for the sake of giving a neat appearance. The top of the thread is turned off 0.010 inch to allow the scriber F to slide freely on the screw. The barrel I is used for raising and lowering the slide, but instead of having the graduations placed directly upon it, they are made upon the sleeve C, which fits over a shoulder on the barrel. ”

“ A screw D, binds the jaws together, and hinders the selvage from going inwards. Upon the side cross beam of the loom, seen in section at I, a bolt is fixed which carries a nut F at its end, into which a screwed iron rod E enters, on one of whose ends is the handle B. The other extremity of the screw E is adapted by a washer and pin to the back of the pincers at the point H, so that by turning the handle to the right or the left, we draw onwards or push backwards the pincers and the stuff at pleasure. The warp of the web is made of black linen yarn. ”

“ The same engineer also contrived a hand tool for cutting screws with greater accuracy than had formerly been attained in that process. A mechanic often finds it necessary to form a screw-thread on a bolt, and also to produce in metal a hollow screw. The reader may have observed gas-fitters and other workmen performing the first operation by an instrument having the same general appearance as Fig. 28. This contains hard steel dies, which are made to press on the bolt or pipe, so that when the guide-stock is turned by the handles, the required grooves are cut out. ”

“ Nevertheless, these threads are made to occupy the same length, in both screw and nut, as though they did enter each other: so that the two parts running parallel to each other, leave a square interstice b, all along both nut and screw: into which balls of brass, or soft iron are [82] introduced, which at once restore the screw-property without it’s friction: a friction so considerable in the common screw, that it always surpasses the effective power, since it remains closed, (in a vice for example) while holding any object squeezed with all the force a man can apply. ”

“ Machines embodying the principle of the master lead screw are found in constant use by industry at the present time for specialized application. Whenever technological changes again reopen the topic of thread-cutting to a new degree of accuracy or call for a reevaluation of popular methods for any other reason, we may expect to see another resurgence of the master-screw method, for no other design eliminates so many variables or rests on such firm and fundamental natural principles as the machine of Das mittelalterliche Hausbuch of 1483, the earliest such machine now known. ”

“ The introduction of gearing between the spindle and the lead screw, for whatever purpose, could not help but introduce variable factors caused by inaccuracies in the gears themselves and in their mounting. These were of little consequence for common work, particularly when coupled to a screw which, itself, was of questionable accuracy. The increasing refinements demanded in scientific instruments and in machine tools themselves after they had reached a relatively stable form dictated that attention be dedicated to improved accuracy of the threaded components. ”