Screw (hardware)

“ 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. ”

“ A lead screw should preferably be as near as possible to the middle of the lathe shears, and as close to the surface as possible, so as to bring it as nearly in line with the strain on the tool as possible, but on account of the cuttings, which falling upon the screw would cause it to wear rapidly, it is usual to locate it on one side, so as to protect it from the cuttings. ”

“ A defect common to all devices in which the tool is thrown out of level, is that the binding screw does not bed fair upon the tool, and as a result it is apt, if screwed home very firmly, as is necessary to hold boring tools that stand far out from the tool post, to spread the screw end as in Fig. ”

“ 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. ”

“ A machine screw is a small screw, such as in Fig. 387, the diameter of the body being made to the Birmingham wire gauge, the heads being formed by upsetting the wire of which they are made. They have saw slots s for a screw driver, the threads having special pitches, which are given hereafter. The forms of the heads are as in Fig. 387, a being termed a Fillister, b a countersink, and c a round head. The difference between a Fillister head of a machine screw and the same form of head in a cap screw is that the former is upset cold, and the latter is either forged or cut out of the solid metal. ”

“ But the fact remains that no guide screw yet made is true, and no true screw can be made apart from the use of devices which are unknown in the machine shop. Actually no screw ever has been, or probably ever will be, made perfect, but the variation from truth has been in some cases only 1/25,000 or 1/30,000 part of an inch. The microscope is brought into requisition for testing standard screws, but commercial screws simply have to pass the test of gauges. ”

“ The screws and nuts about a machine should be provided with sharp, deep threads, and work easily though not loosely. A maker can almost always be judged by the kind of screws he cuts. The nuts and screw-heads should be case-hardened and be neat and square on the corners, and not rounded by the nickel polisher. ”

“ On account of the spring of the parts, which occurs when the strain is transmitted from one part to another, it is desirable when using the chuck as a universal one to first operate one screw to grip the work and then pass to the others and operate them so that they may receive the pressure direct from the screw head and not entirely through the medium of the rack, and there will be found enough movement of the screws when thus operated to effect the object of relieving the rack to some extent from strain. ”

“ Figure 21 shows a plan view [7] of the machine, and figure 22 a detailed view of the sine-bar mechanism actuated by the master screw, 6, to modify the effective pitch of the lead screw in accordance with the realities of practice as stated in the preamble of the patent:
This invention relates to material working machines, and particularly to machines such as hob grinders and the like, wherein the work is reciprocated through the agency of a lead screw. ”

“ In short, the machine rolls out the screws, instead of cutting them out. We have lately seen photographs of some of these screws which have been partially eaten away with acid, for the purpose of showing the fibrous nature of the metal. It is curious to note how the fibre is bent in and out as it follows the direction of the thread on the screw. This method of manufacture is said to present advantages apart from better quality. The screws can be more quickly produced at a less cost, and there is a great saving of material, for nothing is cut away to waste. ”

“ The tailstock or poppet-head screw is a right hand because the nut moves in this case. The object of employing right-hand screws in some cases, and left-hand ones in others, is that it comes most natural in operating a screw to move it from right to left to unscrew, and from left to right to screw up a piece, this being the action of a right-hand screw, left-hand screws being comparatively rarely used in mechanism, save when to attain the object above referred to. ”

“ In this way, it was possible to thread steel without tearing, as the cutting pressure could readily be felt and the tool could release itself from too heavy a cut. Size on several screws could be repeated by setting the tool to produce the desired diameter when its supporting arm came to rest against the frame of the machine. The screws used in the machine itself were apparently made in just such a way. They were not cut with a die as the thread blends very gradually into the body of the screw without the characteristic marks left by the cutting edges of a die. ”

“ History does not reveal the earliest forms of any primitive machines nor does it reveal much about the various early stages in evolution toward more complex types. At best we have discovered and dated certain developments as existing in particular areas. Whether these forms were new at the time they were first found or how widely dispersed such forms may have been is unknown. Surviving evidence is in the form of pictures or drawings, such as the little-known screw-cutting lathe of 1483 (fig. 1) shown in Das mittelalterliche Hausbuch. ”

“ To prevent the sleeve m from moving back with l it is provided with a shoe o, pressed by the spring r against x, thus producing a friction between m and x that holds m while l slides through it. r′ is to regulate the tension of the spring at r. y is merely a sleeve to protect the clutch mechanism from dust, &c.
Box tools for screw machines are used for a great variety of special work. They are simply boxes or heads carrying tools and a work-steadying rest.
Fig. 714.
Fig. 714 represents a box tool for a screw machine. ”

“ Work may be very securely fastened together by the employment of what are called differential screws, the principle of whose action may be explained with reference to Fig. 415, which is extracted from “Mechanics.” It represents a piston head and piston rod secured together by means of a differential screw nut. The nut contains an internal thread to screw on the rod, and an external one to screw into the piston head, but the internal thread and that on the rod differ from the external one, and that in the head by a certain amount, as say one tenth of the pitch. ”

“ 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 screws used by carpenters, smiths, and others, for fastening wood or metal-work together, are generally made by machinery. A piece of wire of the required thickness and length is first cut off, which is then placed in a hole or mould, with its upper orifice “countersunk” as in the annexed cut, and the head of the screw is formed by beating the upper part of the piece of wire into the counter-sinking of the mould. ”

“ Any of the augers or bits that are used in boring by hand may be used in a boring machine, but it is obvious that, as the bit or auger is forced to its feed by hand or foot, and as its revolution is very rapid, the screw point, which is intended as an aid in feeding when the bit is used by hand, is not necessary. ”

“ 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. ”

“ The bit handle is the entire tool, the square socket or opening being made in the end of the handle, in which the shanks of bits may be inserted.
The screw driver is formed on the end of the screw bar, attached to the outer jaw of the wrench, and is taken out from the hollow of the handle when required for use. ”

“ At this stage the screw has to be balanced. This is of great importance, since the screw that is unbalanced loses a great amount of efficiency owing to the consequent vibration when it rotates. In full-size practice it would be highly dangerous to use a screw that is not balanced.
A piece of wire is passed through the hole previously drilled, and the heavier blade carefully glasspapered down (with No. 00 glasspaper to finish) until the screw poises in a horizontal plane. Fig. 47 shows the sort of brush to use for polishing, and Fig. 48 the finished screw. ”

“ 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 advantages of the screw machine are, that the work requires no centring since it is held in a chuck, that forging operations are dispensed with, that any number of pieces may be made of uniform dimensions without any measuring operations save those necessary when adjusting the tool for the first piece, and that it does not require skilled labor to operate the machine after the tools are once set. ”

“ Screw means to machine a thread on the butt-end of the wire, and in this way the wire can make connection with the desired place by being screwed into a metal fitting, thus eliminating the disadvantage of the unsatisfactory loop. ”

“ 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. ”

“ When a lead screw is long it requires to be supported, otherwise, either its weight will be supported or lifted by the feed nut in gear, or if that nut does not lift the screw, the thread cut will be finer than that due to the pitch of the lead screw, by reason of its deflection or sag. ”

“ As any boy knows that has ever used tools, heating a screwdriver, if it is a good one, ruins the temper and makes it easy to break when struggling with a refractory screw.
As soon as the blade had gotten sufficiently heated, he applied it quickly to the lead sinker and caused it to melt and fuse around the needle. Two or three applications of the hot screwdriver were necessary before the job could be called complete, and then Garry sat back and surveyed his work with satisfaction. ”

“ If the gauge be screwed up too tightly the value of the measurement is destroyed, since a copper wire can easily be crushed, and in addition the accurate screw may be permanently damaged. To avoid the possibility of this happening, screw gauges are provided with a ratchet which prevents an excessive force being applied to the screw. If the pitch of the screw in the gauge be 1/20th of an inch, and the circular scale consist of 50 divisions, then for each revolution of the screw, the surface B will travel a distance equal to the pitch, that is 1/20th of an inch. ”

“ 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. ”