Fig. 386Fig. 386.
Fig. 386.
Cap screws are made with heads either hexagon, square, or round, and also with a square head and round collar, as inFig. 386, the square heads being of larger diameter than the iron from which they were made. When the heads of cap screws are finished they are designated as “milled heads.”
Fig. 387Fig. 387.
Fig. 387.
A machine screw is a small screw, such as inFig. 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 slotssfor a screw driver, the threads having special pitches, which are given hereafter. The forms of the heads are as inFig. 387,abeing termed a Fillister,ba countersink, andca 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.
Fig. 388Fig. 389Fig. 388.Fig. 389.
Fig. 388.Fig. 389.
When the end of a screw abuts against the work to secure it, it is termed a set screw. The ordinary form of set screw is shown inFig. 389, the head being square and either black or polished as may be required. The ends of the set screws of commerce, that is to say, that are kept on sale, are usually either pointed as ata,Fig. 388, slightly bevelled as atb, or cupped as atd. If left flat or only slightly bevelled as atb, they are liable, if of steel and not hardened, or if of iron and case-hardened only, to bulge out as atc. This prevents them from slacking back easily or prevents removal if necessary, and even though of hardened steel they do not grip very firmly. On this account their points are sometimes made conical, as ata. This form, however, possesses a disadvantage when applied to a piece of work that requires accurate adjustment for position, inasmuch as it makes a conical indentation in the work, and unless the point be moved sufficiently to clear this indentation the point will fall back into it; hence the conical point is not desirable when the piece may require temporary fixture to find the adjustment before being finally screwed home. For these reasons the best form of set screw end is shown atd, the outside of the end being chamfered off and the inside being cupped, as denoted by the dotted lines. This form cuts a ring in the work, but will hold sufficiently for purposes of adjustment without being screwed home firmly.
Fig. 390Fig. 390.
Fig. 390.
In some cases the end of the set screw is tapped through the enveloping piece (as a hub) and its end projects into a plain hole in the internal piece of the work, and in this case the end of the thread is turned off for a distance of two or three threads, as atainFig. 390. Similarly, when the head of the screw is to act or bear upon the work, the thread may be turned off as atbin the figure.
Fig. 391Fig. 391.
Fig. 391.
When a bolt has no head, but is intended to screw into the work at one end, and receive a nut at the other, it is termed a stud or standing bolt. The simplest form of standing bolt is that in which it is parallel from end to end with a thread at each end, and an unthreaded part in the middle, but since standing bolts or studs require to remain fixed in the work, it is necessary to screw them tightly into their places, and therefore firmly home. This induces the difficulty that some studs may screw a trifle farther into the work than others, so that some of the stud ends may project farther through the nuts than others, giving an appearance that the studs have been made of different lengths. The causes of this may be slight variations in the tapping of the holes and the threading of the studs. If those that appear longest are taken out and reduced to the lengths of the others, it will be found sometimes that the stud on the second insertion will pass farther into the work than at the first, and the stud will project less through the nut than the others. To avoid this those protruding most may be worked backward and forward with the wrench and thus induced to screw home to the required distance, but it is better to provide to the stud a shoulder against which it may screw firmly home; thus inFig. 391is a stud, whose endais to screw into the work, partbis to enter the hole in the work (the thread in the hole being cut away at the mouth to receiveb). In this case the shoulder betweenbandcscrewing firmly against the face of the work, all the studs being made of equal length from this shoulder to ende, then the thickness of the flange or work secured by the nut being equal, the nuts will pass an equal distance on endd, andewill project equally through all the nuts. The length of the plain partcis always made slightly less than the thickness of the flange or foot of the work to be bolted up, so that the nut shall not meetcbefore gripping the flange surface.
There are, however, other considerations in determining the shape and size of the partsaandcof studs.
Thus, suppose a stud to have been in place some time, the nut on endebeing screwed firmly home on the work, and perhaps somewhat corroded one. Then the wrench pressure applied to the nut will be in a direction to unscrew the stud out of the work, and if there be less friction betweenaand the thread in the work than there is betweendand the thread in the nut, the stud and not the nut will unscrew. It is for this purpose that the endarequires firmly screwing into the work. But in the case of much corrosion this is not always sufficient, and the threadais therefore sometimes made of a larger diameter than the thread atd. In this case the question at once arises, What shall be the diameter of the plain partc?
Fig. 392Fig. 392.
Fig. 392.
If it be left slightly larger thand, but the depth of the thread less thana, then it may be held sufficiently firmly by the fit of the threads (without the aid of screwing against a shoulder) to prevent unscrewing when releasing the nut, and may be screwed within the work until its end projects the required distance; thus all the studs may project an equal distance, but there will be the disadvantage that when the studs require removing and are corroded the plain part is apt to twist off, leaving the endaplugging the hole. The plain partcmay be left of same diameter asa, both being larger thand; but in this case the difficulty of having all the studs project equally when screwed home, as previously mentioned, is induced; hencecmay be larger thana, and a shoulder left atb, as in the figure; this would afford excellentfacility for unscrewing the stud to remove it, as well as insuring equal projection ofe. The best method of all is, so far as quality goes, to make the plain partcsquare, as inFig. 392, which is an English practice, the square affording a shoulder to screw up against and secure an equal projection while serving to receive a wrench to put in or remove the stud. In this case the holes in the flange or piece bolted up being squared, the stud cannot in any case unscrew with the nut. The objection to this squared stud is that the studs cannot be made from round bar iron, and are therefore not so easily made, and that the squaring of the holes in the flange or part of the work supported by the stud is again extra work, and for these reasons studs with square instead of cylindrical mid-sections have not found favor in the United States.
Fig. 393Fig. 393.
Fig. 393.
An excellent method of preventing the stud from unscrewing with the nut is to make the endalonger than the nut end, as inFig. 393, so that its threads will have more friction; and this has the further advantage that in cast iron it serves also to make the strength of the thread equal to that of the stud. As the faces of the nuts are apt when screwed home to score or mark the face of the work, it adds to the neatness of the appearance to use a washerwbeneath the nut, which distributes the pressure over a greater area of work surface.
In some practice the endsaof studs are threaded taper, which insures that they shall fit tight and enables their more easy extraction.
Fig. 394Fig. 394.
Fig. 394.
An excellent tool for inserting studs of this kind to the proper distance is shown inFig. 394. It consists of a square bodyathreaded to receive the stud whose end is shown atc. The upper end is threaded to receive an adjusting screwb, which is screwed in so that its enddmeets the endcof the stud. It is obvious thatbmay be so adjusted that whenais operated by a wrench applied to its body until its end face meets the work and the stud is inserted to the proper depth, all subsequent studs may be put into the same depth.
Fig. 395Fig. 395.
Fig. 395.
When the work pivots upon a stem, as inFig. 395, the bolt is termed a standing pin, and as in such cases the stem requires to stand firm and true it is usual to provide the pin with a collar, as shown in the figure, and to secure the pivoted piece in place with a washer and a taper pin because nuts are liable to loosen back of themselves. Furthermore, a pin and washer admit of more speedy disconnection than a nut does, and also give a more delicate adjustment for end fit.
In drilling the tapping holes for standing bolts, it is the practice with some to drill the holes in cast iron of such a size that the tap will cut three-quarters only of a full thread, the claim being that it is as strong as a full thread. The difference in strength between a three-quarter and a full thread in cast iron is no doubt practically very small indeed, while the process of tapping is very much easier for the three-quarter full thread, because the tap may, in that case, be wound continuously forward without backing it at every quarter or half revolution, as would otherwise be necessary, in order to give the oil access to the cutting edges of the tap—and oil should always be used in the process of tapping (even though on cast iron it causes the cuttings to clog in the flutes of the tap, necessitating in many cases that the tap be once or twice during the operation taken out, and the cuttings removed) because the oil preserves the cutting edges of the tap teeth from undue abrasion, and, therefore, from unnecessarily rapid dulling. With a tap having ordinarily wide and deep flutes, and used upon a hole but little deeper than the diameter of the tap, the cuttings due to making a three-quarter full thread will not more than fill the flutes of the tap by the time its duty is performed. We have also to consider that with a three-quarter full thread it is much easier to extract the standing bolt when it is necessary to do so, so that all things considered it is permissible to have such a thread, providing the tapping hole does not pass through into a cylinder or chamber requiring to be kept steam-tight, for in that case the bolt would be almost sure to leak. As a preventive against such leakage, the threads are sometimes cut upon the standing bolts without having a terminal groove, and are then screwed in as far as they will go; the termination of the thread upon the standing bolt at the standing or short end being relied upon to jam into and close up the thread in the hole. A great objection to this, however, is the fact that the bolts are liable to screw into the holes to unequal depths, so that the outer ends will not project an equal distance through the nuts, and this has a bad appearance upon fine work. It is better, then, in such a case, to tap the holes a full thread, the extra trouble involved in the tapping being to some extent compensated for in the fact that a smaller hole, which can be more quickly drilled, is required for the full than for the three-quarter thread.
The depth of the tapping hole should be made if possible equal to one and a half times the diameter of the tap, so that in case the hole bottoms and the tap cannot pass through, the taper, and what is called in England the second, and in the United States the plug tap, will finish the thread deep enough without employing a third tap, for the labor employed in drilling the hole deeper is less than that necessary to the employment of a third tap. If the hole passes through the work, its depth need not, except for cast-iron holes, be greater than1⁄8inch more than the diameter of the bolt thread, which amount of excess is desirable so that in case the nut corrodes, the nut being as thick as the diameter of the tap, and therefore an inch less than the depth of the hole at the standing end, will be more likely to leave the stud standing than to carry it with it when being unscrewed.
Fig. 396Fig. 396.
Fig. 396.
Fig. 397Fig. 397.
Fig. 397.
When it is desirable to provide that bolts may be quickly removed, the flanges may be furnished with slots, as inFig. 396, so that the bolts may be passed in from the outside, and in this case it is simply necessary to slacken back the nut only. It is preferable, however, in this case to have the bolt square under the head, as inFig. 397, so as to prevent the bolt from turning when screwing up or unscrewing the nut. The bolt is squared ata, which fits easily into the flange. The flanges, however, should in this case be of ample depth or thickness to preventtheir breakage, twice the depth of the nut being a common proportion.
Fig. 398Fig. 398.
Fig. 398.
Fig. 399Fig. 399.
Fig. 399.
In cases where it is inconvenient for the bolt head to pass through the work aTgroove is employed, as inFig. 398. In this case the bolt head may fit easily ata bto the sidesa bof the groove, so that while the bolt head will slide freely along the groove, the head, being square, cannot turn in the slot when the nut is screwed home. This, however, is more efficiently attained when there is a square part beneath the bolt head, as inFig. 399, the squareaof the bolt fitting easily to the slotbof the groove.
Fig. 400Fig. 400.
Fig. 400.
Fig. 401Fig. 401.
Fig. 401.
Fig. 402Fig. 402.
Fig. 402.
When it is undesirable that the slots run out to the edge of the work they may terminate in a recess, as atainFig. 400, which affords ingress of the bolt head to the slot; or the bolt head may be formed as inFig. 401, the widtha bof the bolt head passing easily through the topa bof the slot, and the bolt head after its insertion being turned in the direction of the arrow, which it is enabled to do by reason of the rounded cornersc d. In this case, also, there may be a square under the head to prevent the bolt head from locking in the slot, but the corners of the square must also be rounded as inFig. 402.
Fig. 403Fig. 403.
Fig. 403.
The underneath or gripping surface of a bolt head should be hollow, as atainFig. 403, rather than rounding as atb, because, if rounding, the bolt will rotate with the nut when the latter grips the work surface. It should also be true with the axial line of the bolt so as to bear fairly upon the work without bending. The same remarks apply to the bedding surface of the nut, because to whatever amount the face is out of true it will bend the threaded end of the bolt, and this may be sufficient to cause the bolt to break.
Fig. 404Fig. 404.
Fig. 404.
InFig. 404, for example, is shown a bolt and nut, neither of which bed fair, being open ataandbrespectively, and it is obvious that the strain will tend to bend or break the bolt across the respective dotted linesc,d. In the case of the nut there is sufficient elasticity in the thread to allow of the nut forcing itself to a bed on the work, the bolt bending; but in the case of the bolt head the bending is very apt to break off the bolt short in the neck under the head. In a tap bolt where the wrench is applied to the bolt head, the rotation, under severe strain, of the head will usually cause it to break off in all cases where the bolt is rigidly held, so that it cannot cant over and allow the head to bed fair.
A plain tap bolt should be turned up along its body, because if out of true the hole it passes through must be made large enough to suit the eccentricity of the bolt, or else a portion of the wrench pressure will be expended in rotating the bolt in the hole instead of being expended solely in screwing the bolt farther into the work.
It is obvious therefore, that if a tap bolt be left black the hole it passes through must be sufficiently large to make full allowance for the want of truth in the bolt. For the same reasons the holes for tapped bolts require to be tapped very true.
Black studs possess an advantage (over tap bolts) in this respect, inasmuch as that if the holes are not tapped quite straight the error may be to some extent remedied by screwing them fully home and then bending them by hammer blows.
Nuts are varied in form to suit the nature of the work. For ordinary work, as upon bolts, their shape is usually made to conform to the shape of the bolt head, but when the nut is exposed to view and the bolt head hidden, the bolt end and the nut are (for finished work) finished while the bolt heads are left black.
Fig. 405Fig. 405.
Fig. 405.
Fig. 406Fig. 406.
Fig. 406.
The most common form of hexagon nut is shown inFig. 405, the upper edge being chamfered off at an angle of about 40°. In some cases the lower edge is cut away at the corners, as inFig. 405ata, the object being to prevent the corners of the nut from leaving a circle of bearing marks upon the work, but this gives an appearance at the corners that the nut does not bed fair. Another shape used by some for the end faces of deep nuts, that is to say, those whose depth exceeds the diameter of the bolt, is shown inFig. 406. Nuts of extra depth are used when, from the nut being often tightened and released, the thread wear is increased, and the extra thread length is to diminish the wear.
Fig. 407Fig. 407.
Fig. 407.
To avoid the difficulty of having some of the bolt ends project farther through some nuts than others on a given piece of work, as is liable to occur where the flanges to be bolted together are not turned on all four radial faces, the form of nut shown inFig. 407is sometimes employed, the thread in the nut extending beyond the bolt end.
Fig. 408Fig. 408.
Fig. 408.
As an example of the application of this nut, suppose a cylinder cover to be held by bolts, then the cylinder flange not being turned on its back face is usually of unequal thickness; hence to have the bolt ends project equally through the nuts, each bolt would require to be made of a length to suit a particular hole, and this would demand that each hole and bolt be marked so that they may be replaced when taken out, without trying them in their places. Another application of this nut is to make a joint where the threads may be apt to leak. In this case the mouth of the hole is recessed and coned at the edge; the nut is chamfered off with a similar cone, and a washerw,Fig. 408, is placed beneath the nut to compress and conform to the coned recess; thus with the aid of a cement of some kind, as red or white lead (usually red lead), a tight joint may be made independent of the fit of the threads.
Fig. 409Fig. 409.
Fig. 409.
When the hole through which the bolt passes is considerably larger in diameter than the bolt, the flange nut shown inFig. 409is employed, the flange covering the hole. A detached washer may be used for the same purpose, providing that its hole fit the bolt and it be of a sufficient thickness to withstand the pressure and not bend or sink into the hole.
Fig. 410Fig. 410.
Fig. 410.
Fig. 411Fig. 411.
Fig. 411.
Fig. 412Fig. 412.
Fig. 412.
Circular nuts are employed where, on account of their rotating at high speed, it is necessary that they be balanced as nearly as possible so as not to generate unbalanced centrifugal force.Fig. 410represents a nut of this kind: two diametrically opposite flat sides, asa, affording a hold for the wrench. Other forms of circular nuts are shown inFigs. 411and412. These are employed where the nuts are not subject to great strain, and where lightness is an object.
That inFig. 411is pierced around its circumference with cylindrical holes, asa,b,c, to receive a round lever or rod or a wrench, such as shown inFig. 459.
That shown inFig. 412has slots instead of holes in its circumference, and the form of its wrench is shown inFig. 461.
Fig. 413Fig. 413.
Fig. 413.
When nuts are employed upon bolts in which the strain of the duty is longitudinal to the bolt, and especially if the direction of motion is periodically reversed, and also when a bolt is subject to shocks or vibrations, a single nut is liable to become loose upon the bolt, and a second nut, termed a check nut, jamb nut, or safety nut, becomes necessary, because it is found that if two nuts be employed, as inFig. 413, and the second nut be screwed firmly home against the first, they are much less liable to come loose on the bolt.
Considerable difference of practice exists in relation to the thickness of the two nuts when a check nut is employed. The first or ordinary nut is screwed home, and the second or check nut is then screwed home. If the second nut is screwed home as firmly as the first, it is obvious that the strain will fall mainly on the second. If it be screwed home more firmly than the first, the latter may be theoretically considered to be relieved entirely of the strain, while if it be screwed less firmly home, the first will be relieved to a proportionate degree of the strain. It is usual to screw the second home with the same force as applied to the first, and it would, therefore, appear that the first nut, being relieved of strain, need not be so thick as the first, but it is to be considered that, practically, the first nut will always have some contact with the bolt threads, because from the imperfections in the threads of ordinary bolts the area and the force of contact is not usually the same nor in the same direction in both nuts, unless both nuts were tapped with the same tap and at about the same time.
When, for example, a tap is put into the tapping machine, it is at its normal temperature, and of a diameter due to that temperature, but as its work proceeds its temperature increases, notwithstanding that it may be freely supplied with oil, because the oil cannot, over the limited area of the tap, carry off all the heat generated by the cutting of a tap rotated at the speeds usually employed in practice. As a result of this increase of temperature, we have a corresponding increase in the diameter of the tap, and a variation in the diameter of the threads in the nuts. The variation in the nuts, however, is less than that in the tap diameter, because as the heated tap passes through the nut it imparts some of its heat to the nut, causing it also to expand, and hence to contract in cooling after it has been tapped, and, therefore, when cold, to be of a diameter nearer to that of the tap.
Furthermore, as the tap becomes heated it expands in length, and its pitch increases, hence here is another influence tendingto cause the pitches of the nut threads to vary, because although the temperature of the tap when in constant use reaches a limit beyond which, so long as its speed of rotation is constant, it never proceeds; yet, when the tap is taken from the machine to remove the tapped nuts which have collected on its shank, and it is cooled in the oil to prevent it from becoming heated any more than necessary, the pitch as well as the diameter of the tap is reduced nearer to its normal standard.
So far, then, as theoretical correctness, either of pitch or diameter in nut threads, is concerned, it could only be attained (supposing that the errors induced by hardening the tap could be eliminated) by employing the taps at a speed of rotation sufficiently slow to give the oil time to carry off all the heat generated by the cutting process. But this would require a speed so comparatively slow as not to be commercially practicable, unless followed by all manufacturers. Practically, however, it may be considered that if two nuts be tapped by a tap that has become warmed by use, they will be of the same diameter and pitch, and should, therefore, have an equal area and nature of contact with the bolt thread, supposing that the bolt thread itself is of equal and uniform pitch. But the dies which cut the thread upon the bolt also become heated and expanded in pitch. But if the temperature of the dies be the same as that of the tap, the pitches on both the bolt and in the nut will correspond, though neither may be theoretically true to the designated standard.
In some machines for nut tapping the tap is submerged in oil, and thus the error due to variations of temperature is practically eliminated, though even in this case the temperature of the oil will gradually increase, but not sufficiently to be of practical moment.
Let it now be noted that from the hardening process the taps shrink in length and become of finer pitch, while the dies expand and become of coarser pitch, and that this alone precludes the possibility of having the nut threads fit perfectly to those on the bolt. It becomes apparent, then, that only by cutting the threads in the lathe, and with a single-toothed lathe tool that can be ground to correct angle after hardening, can a bolt and nut be theoretically or accurately threaded. Under skilful operation, however, both in the manufacture of the screw-cutting tools and in their operation, a degree of accuracy can be obtained in tapped nuts and die-threaded bolts that is sufficient with a single nut for ordinary uses, but in situations in which the direction of pressure on the nut is periodically reversed, or in which it is subject to shocks or vibrations, the check nut becomes necessary, as before stated.
Fig. 414Fig. 414.
Fig. 414.
An excellent method of preventing a nut from slackening back of itself is shown in the safety nut inFig. 414; it consists of a second nut having a finer thread than the first one, so that the motion of the first would in unscrewing exceed that of the second, hence the locking is effectually secured.
Fig. 415Fig. 415.
Fig. 415.
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 toFig. 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. The nut itself is furnished with a hexagonal head, and when screwed into place draws the two parts together with the same power as a screw having a pitch equal to the difference between the two pitches.
Fig. 416Fig. 416.
Fig. 416.
When putting the parts together the nut is first screwed upon the rodb. The outside threads are then entered into the thread in the pistonc, and by means of a suitable wrench the nut is screwed into the proper depth. As shown in the engraving, the nut goes on to the rod a couple of threads before it is entered in the piston. The tightening then takes place precisely as though the nut had a solid bearing on the piston and a fine thread on the rod, the pitch of which is equal to the difference between the pitches of the two threads.Fig. 416shows its application to the securing of a pump plunger upon the end of a piston-rod. In this case, as the rod does not pass through the nut, the latter is provided with a cap, which covers the end of the rod entirely.
Fig. 417Fig. 417.
Fig. 417.
The principle of the differential screw may be employed to effect very fine adjustments in place of using a very fine thread, which would soon wear out or wear loose. Thus inFig. 417is shown the differential foot screws employed to level astronomical instruments.c dis a foot of the instrument to be levelled. It is threaded to receive screwa, which is in turn threaded to receive the screwb, whose foot rests in the recess or cup ine f. Suppose the pitch of screwais 30 per inch, and that ofbis 40, and we have as follows. Ifaandbare turned together the footc dis moved the amount due to the pitch ofa. Ifbis turned within a the foot is moved the amount due to the pitch ofb. Ifais turned the friction of the foot ofbwill holdbstationary, and the motion ofc dwill equal the difference between the pitches of the threads ofaandb. Thus one revolution ofaforward causes it to descend throughc d1⁄30inch (its pitch), tending to raisec d1⁄30inch. But while doing this it has screwed down upon the thread ofb1⁄40inch (the pitch ofb) and this tends to lowerc d, hencec dis moved1⁄120inch, because1⁄30-1⁄40=1⁄120.
To cause a single nut to lock itself and dispense with the second or jamb nut, various expedients have been employed. Thus inFig. 418is shown a nut split on one side; after being threaded the split is closed by hammer blows, appearing as shown in the detached nut. Upon screwing the nut upon the bolt the latter forces the split nut open again by thread pressure, and this pressure locks the nut. Now there will be considerable elasticity in the nut, so that if the thread compresses on its bearing area, this elasticity will take up the wear or compression and still cause the threads to bind. Sometimes a set screw is added to the split, as inFig. 419, in which case the split need not be closed with the hammer.
Another method is to split the nut across the end as shown inFig. 420, tapping the nut with the split open, then closing the split by hammer blows. Here as before the nut would pass easily upon the bolt until the bolt reached the split, when the subsequent threads would bind. In yet another design, shown inFig. 421, four splits are made across the end, while the face of the nut is hollowed, so that a flat place near each corner meets the work surface. The pressure induced on these corners by screwing the nut home is relied on in this case to spring the nut, causing the thread at the split end to close upon and grip the bolt thread.
Check nuts are sometimes employed to lock in position a screw that is screwed into the work, thus screws that require to be operated to effect an adjustment of length (as in the case of eccentric rods and eccentric straps) are supplied with a check nut, the object being to firmly lock the screw in its adjusted position.
The following are forms of nuts employed to effect end adjustments of length, or to prevent end motion in spindles or shafts that rotate in bearings.
Fig. 422shows two cylindrical check nuts, the inner one forming a flange for the bearing. The objection to this is that in screwing up the check nut the adjustment of the first nut is liable to become altered in screwing up the second one, notwithstanding that the first be held by a lever or wrench while the second is screwed home.
Another method is to insert a threaded feather in the adjustment nut and having at its back a set screw to hold the nut in its adjusted position, as inFig. 423. In this case the protruding head of the set screw is objectionable. In place of the feather the thread of the spindle may be turned off and a simple set screw employed, as inFig. 424; here again, however, the projecting set screw head is objectionable. The grip of an adjustment nut may be increased by splitting it and using a pinching or binding screw, as inFig. 425, in which case the bore of the thread is closed by the screw, and the nut may be countersunk to obviate the objection of a projecting head. For adjusting the length of rods or spindles a split nut with binding screws, such as shown inFig. 426, is an excellent and substantial device. The bore is threaded with a right-hand thread at one end and a left-hand one at the other, so that by rotating the nut the rod is lengthened or shortened according to the direction of rod rotation. Obviously a clamp nut of this class, but intended to take up lost motion or effect end adjustment, may be formed as inFig. 427, but the projecting ears or screw are objectionable.
Where there is sufficient length to admit it an adjustment nut, such as inFig. 428, is a substantial arrangement. The nutais threaded on the spindle and has a taper threaded split nut to receive the nutb. Nutaeffects the end adjustment by screwing upon the spindle, and is additionally locked thereon by screwingbup the taper split nut, causing it to close upon and grip the spindle.