US1794614A - Releasable screw mechanism - Google Patents

Description

Marc 3, 1931. J c HQCHMAN 1,794,614

RELEASABLE SCREW MECHANI SM Original Filed Jan. 30, 1922 SSheets-Sheet 1 Ju/z'zu 6. llarfiman Patented Mar. 3, 1931 PATENT OFFICE JULIUS O. HOGHHAN, OF NEW YORK, N. Y.

RELEASABLE SCREW MECHANISM Application filed January 80, 1922, Serial No. 532,571. Renewed September 8, 1928.

My present invention is shown as embodied in a variety of releasable locking-screw mechanisms. As my primary illustrative disclosure, I show it embodied in a monkey wrench 1 for controlling the locking and releasing of the jaw-locking screw element or worm,

now commonly employed for hand adjustment. It will be obvious, however, that the same mechanism may be used whereversuch a screw lock and release is desired; also that certain of its broadly novel principles and features may be embodied in other devices where it is desired for the operation or conor nut which co-operates with the rec and,

while preserving these within limits, I associate them with other mechanisms including a pilot screw element whereby the locking screw element may be automatically rotated -to permit free sliding movements of themovable jaw in one or the other or both directions, as may be desired; these elements being organized for the purpose and with the result that the sliding jaw may be arranged to open or to close in response 'to endwise pressures, or to be automatically locked against said pressures -in either desired one (if said direc-- tions. Preferably, also there is an-element, preferably a spring, whereby the sliding jaw is pressed toward' the fixed jaw, preferably with sufficient power to. give automatic 0105- ing of the jaws, though 1t may be mere balancing of the weight and friction of the slid-- ing jaw; and in otherembodiments I may -utilize gravity in place of a spring, either as a balance or as a counter-balance.

In the monkey wrench the rotary locking screw element, the longitudinal rack'to which it is threaded, the sliding jaw and the pilot screw element are all so organized that a slight angular movement of the handle of the monkey wrench when applying pressure to I screw a nut or bolt in the desired direction, will operate to throw the parts into locking relation, while reversed pressure on the handle will release the locking element and put the pilot screw element in the automatic screwing relation to said locking element, preferably by imparting slight endwise movement to the pilot screw-element. The locking direction for the pressure is preferably reversible by a simple adjustment; and in both directions, the locking movement brings the handle into solid contact with the shank, thereby relieving its pivotal centre of all strain.

Thus by my invention the monkey wrench becomes capable of operation as an automatic ratchet wrench, the jaws of which will open freely to rotate around the corners of a nut when pressure is applied to the handle in one direction, will close automatically, and will be automatically locked when'pre'ssure is applied to the handle in the opposite direction. Similarly the sliding jaw will slide open under hand pressure for application to the nut or bolt, when the handle is in. the first position, and-will'automatically close, and will look when the handle shifts'under the reverse pressure.

For these purposes, the pitch and areasof the locking screw threads and other thrustbearing surfaces of the rotatin element are such as to afford prohibitive spon'se to the endwise thrusts or pressures applied either. to said sliding jaw through said locking thread or to said locking thread frictional op- 'positlon to any automatic screwmg in rethrough saidisliding jaw; and the pilot screw I element engaging the locking screw element is of the same pitch, as the locking screw thread but on a radius so much smaller that the pitch angle of pilot thread is a slipping angle, referably an angle of very easy slip. By s ight 'endwise displacement of either one of the screw elements in the direction of an endwise applied thrust, the endwise load may be shifted from one screw element to the other with resultant endwise slip or endwise lock, according to which thread is caused to take. the load. A very simple machine element such as a cam or lever may be employed to cause the required endwise shift and the operation of such ma'chine element may be controlled manually or automatically in a great variety of ways. In the monkey wrench, the shift of load occurs just after the instant of substantially no-lead when the pressure 'on the handle is reversed; so that when the new (reverse-screwing) load comes, the. slipscrew will support only the very small pressure necessary to rotate the then unloaded to free its locking screw threads from lock ing engagementwith'the rack. After this worm through the very small angle necessary happens only endwise movement of the sliding jaw can cause any further rotation of the worm and such endwise movement can rotate the worm only at the exact speed required to keep its locking threads out of contact with the rack, because-the pitch of the locking threads and the slip threads is precisely the same. Hence the only load that can ever,

come on the pilot screw is the free worms frictional resistance to rotation and this resistance may be made practically negligible. Hence the .pilot screw may be very-light.

With these basic elements,it is possible to combine many specifically different means for relative movement of the pilot'scrcw with reference to the locking screw whereby the threads'of the latter may be slightly rotated or otherwise moved out of locking frictional contact'with the rack teeth or other relative stationary locking rack or screw element. The essential is that the worm becomes free for rotation and worming along the rack dur ing, and because of, and at the rate compelled by'the worms end-wise movement along the,

tion with two other screw degree of frictional contact may b'e held abslip angle groove of said pilot screw element. 45

The release of the frictional lock may be complete or partial as may be desired and the solutely constant for any period of time.

Consideredmore specifically. in some respects, and' inothers more broadly, my 'invention maybe viewed as including a lock screw element having eo-axial threaded relaelements having the same number of turns per unit length but different pitch diameters, such that the engagement between the threads of greater diameter is either at a non-slip angle, or in any event at an angle which, with the other resistances, will afford a lock against endwise' screwing in response to endwise pressure, while the engagement of the threads of lesser diameter isat a'slip angle; in'combination with means for causing or permitting shift of one or more of the screw elements, to bring the two sets of threads into and out of precise functionally endless-and uniform,

conceivable that for some purposes this relation of'clearances might be reversed. Such reversal would be useful with reference to the broad novelty of my combination considered as a new mechanical movement, as for instance, where power is applied to the rotary lock screw element for the-purpose of producing. or preventing certain desired movements of the slip angle screw element. 7

Considered as a novel mechanical move-- ment usable for translating thrusts or rotative efforts applied to any one of the three elements with the view to producing resultant stresses, movements or locking effects on any other of said elements, the invention may be considered more broadly as a screw element threaded to two other screw elements having the same rate of screw feed, prefer-- ably by having the same number of threads per unit length, but having different pitch diameters so that their stress 'or motion pro: ducing resultants-are different. 7

Changing the method of control will make it possible to cause the locking screw to be variously affected, but in the present wrench, the sliding jaw is-free to follow or obey any longitudinal external force, except when the wrench is exerting turning moment on the nut in the direction selected. The effect of this is to allow free ratcheting when the wrench movement is reversed, solid locking when operating and a tendency to hug the nut at all. times. Because a Worm thread is my present worm locked adjustable mechanism partakes of the nature 'of a stepless ratchet in which the driven member may be caused to move with the driving member through the latters full movement or any desired part thereof, according to the timingof the frie tional lock, and at the's'ame speed or any lesser speed, according to thedegree of frictional look as the positively controlled pilot mechanism. 'While'the locking screw thread and the pilot screw-or slipping thread maybe formed on separate elements, I show at least one form governed and maintained by in the threads of the locking screw elements are made to have much more clearance or looseness of fit than are the slip-angle threads, but this is to avoid the necessity for great accuracy in the endwise shift to make one thread or the other take the load However, either thread can be made to take the load even when the clearance is very small or when the slip thread-clearance is greater than the lock thread clearance. In certain forms shown herein. it is the pilot screw element that is given the endwise shift with reference to the locking screw element in order to free the locking threads from locking engagement, bring them to aninterinediate position, meshing with, but free from, the teeth of the rack, or equivalent screw element, but it will be understood the shift of the relative positions of the parts, is the functionally important feature, and the matter of which element moves'to bring about the shift-has to do with the more specific aspects, and practical applications of the invention.

As before intimated, the shift of control from the locking thread to the slip thread may be only partial or may be momentary. This may be especially desirable under certain conditions as where there is a gravity load on the locking thread and it is-desired tolower. the, load slowly or to a predetermineddistance only. In such case special means may be provided for a graduated or partial transfer of some of the load to the a slip thread element. In such operation,- the torque and thrust stresses on the slip thread may be considerable and thepilot screw element has to be of correspondingly heavier construction. I

. On the other. hand, torque and thrust stresses on the pilot screw maybe almost eliminated by utilizing an important subsidiary feature of my invention. This-contem-- plates making the worm with its locking threads, and the pilot threads capable of slight relative movement longitudinally but not -ci'rcumferentially. This may be accomplished by forming the respective threads on coaxial, preferably concentric, sleeves that are connected by a spline. Then, if desired, -theipilot sleeve element may beprovided with anti-friction thrust-bearings, thereby minimizing the said sleeves frictional resistance to rotation under load, the factor upon which depend the load-taking capability and resulting stress on the pilot screw. The spline I connection also leaves thesliding jaw and the inner pilotsleeve free for a' slight endwi'se movement with respect to the outer locking sleeve, when the pilot screw rotates the locking thread into and out of locking engagement with the rack teeth. Upon locking, this permits the end thrust of the full load to be applied by the sliding jaw to the end of the locking sleeve and through the locking,

thread to the rack, without endwise-stress upon the inner sleeve or its endwise thrustbearing; and upon unlocking, the effect is to immediately permit the outer sleeve to fall free from its end-thrust engagement with the sliding jaw.

It will be noted that my mechanism includes inter-engaging elements capable of solid locking under thrust by frictionalen-i gagementwith each other, in combination with co-acting mechanism controlling the look by positively controlling said frictional contact.

It will also be noted that the locking elements and the pilot elements constitute respectively primary and secondary sets of mechanical transmission elements, the motion transforming ratios ofwhich are fixed and are the same; that the primary elements lock under'load while the secondary elements are idle; that'the secondary elements tend to rotate under load; that the load may be shifted to the secondary elements; and finally that the two sets of elements are so coupled that rotation of the secondary set under load will cause unlocking and rotationof the primary set.

vention applied thereto and with the locking screw .element in the locking position.

Fig. 2 is a vertical sectional elevation. of i the same mechanism with the pilot screw element operating and the lockingscrew element free. I Fig. 3 is a section on the line 3-3, showing the shape of the groove, of the pilot screw. p Figs. 4, 5, 6 and 7am detailed views show- "ng various cam employe to shift the lock the locking screw. r -Fig. 8 is a vertical sectional. view similar toFig. 2, but showing a modification'of my- The above and other features of my novel mechanical movement, as wellas a variety of.

positions-of asimple form ofpilot screw to un-' invention as applied to another well-known form of monkey wrench.

Figs. 9 and 10 are, respectively, end view and side elevation of the sliding jaw'shown in Fig. 8. i

Fig. 11 is a vertical sectional view showing 1 v another modification of my invention as ap I plied-to another type of wrench.

Fig. 12 is a detail elevationof parts shown i IFig. 11, looking from the left.

- embodying a form of my invention in which the relative movement for shifting the load from the locking thread to make it take effecton the pilot thread may be a partial or intermittent release .applied by hand at will.

Fig. 15 is a detail-section on the line 1515, Fig. 14.

Fig. 16 is another vertical sectional View showing another modification of my invention as applied to a lifting jack.

Fig. 17 is a section on the line 1717, Fig. 16. j

Fig. 18 is a longitudinal section of a quite I embodiment of the essential features of my invention, as applied for quick locking adjustment and release ofthe jaws ofa vise, with particular provision for a powerful clamping'aetion.

Fig. 19 is an enlarged detail of the locking and pilot thread elements of Fig. 18.

Referring to Figs. 1 and 2 of the drawings,

1 is the locking thread adapted for rotation and longitudinal screwing movement in mesh, but notnecessarily in engagement, with the relatively stationary locking screw element 2, which in this case is a rack, the

j stresses are all relative, it is convenient, for

rack being,.functionally considered, a nar-' row segment of a female screw thread. The locking thread 1 isformed ,on a sleeve 3 which is rotatablymountedin'and carried by the jaw 4, being, in-Zthis case, locatedin a recess between the thrust surface 4 and the bracket member 4. The jaw 4 has sliding engagement with shank 5 to which it is suitably secured by strap or loop portions 4, 4". The co-operating j aw=6is rigidwith sh'ank 5. Though the significant movements and descriptive purposes, to consider the jaw 6, shank 5 and rack 2 as fixed and other parts as movable with reference thereto; and,'al-

though the working pressures on jaws 4 and 6 are equal and opposite, the manipulating pressures are on one-jaw only, and it is con-- venient to consider the sliding jaw 4 as the load carrylng member.

The pilot screw 7 hasa pilotth-readdnthe' form of a groove 8 which is in threaded engagement with the interior projecting lugs or thread eleme'nts9. Said interior thread elements 9 may be formed, directly -on the inhas the locking terior of the sleeve 3which thread on the exterior 'thereoijPrferably, however,

sleeve 3 bymeans of screw 11, fitted into a spline groove 12 so that sleeve 3 is free for slight relative movement longitudinally but is locked to sleeve 10 so far-as concerns 'rotary movement.

The pilot thread 8 has the same number of turns per inch as looking thread 1, but the said threads '9' are in a separate sleeve member 10 which is splined to locking pitch is steep enough to permit easy slip and rotation of "one of the pilot elements 7 or 9, by the other, in response to endwise pressure of either or both with respect to the other. In thevpresent case the pilot screw 7. is non- -rotatable with respect to jaws 4 and 6 and shank 5, so that sleeves 10 and 3 and locking thread 1 carried by the latter, are the elements that rotate when there is relative longitudinal movement.

Whether the locking thread or the pilotthread will control will depend on whether i or not the pilot 'screw 7 isjendwise supported with its threads 8 in phase or registry with the locking threads 1.- If out of phase, as

when screw 7 is in the. lowered position, the

pilot screw and the locking screw threads 1 will not thereby engage and lock against rack 2, because said longitudinal movement will rotate the locking worm thread -1 at exactly the required rate to keep said thread 1' out of frictional lock engagement with the teeth of rack 2. Moreover, when the pilot screw 7 is deprived of its endwise support,

the locking threads 1 will immediately engage-the teethof rack 2.andwill lock the jaw 4 against further retreat. Hence; in

order to have the sliding 'jaw eitherfreebr- "locked at will, it is only necessaryto give the pilot screw 7 a slight endwise shift. 4

plished by providing the lower partof shank 5 with a handle member preferably in the form of a light sheet metal-'casing-i13, piv- :no' j .surface 15, in position where it will apply I otedfon bolt 1 4-an d carrying a suitablecam As shown in the-drawings, thisis accomendwise thrust andsupport upon said pilot screw 7 when the handle swings in one direction as for the screwing pressure; and

will remove said thrust and support when opposite direction.

the pressure is applied on the handle in the The shank 5 has a transverse. member '16 secured by studs 17 andserew 18, .which is formed with a slot 19, engaged. by a spline pin 20 extending through the lowerend of thus exerts upward pressure on'sli g jaw the pilotscrew 7. The pilot screw 7 is nor- 'ple '24, which latter is 4, whereby the jaws will automatically close when unlocked from the rack 2. i The cam surface may be aiforded by a stud member 25, mounted in an end piece 26,

secured by cross bolts or rivets 27 in the bottom of handle 13. This cam stud is made rotatable so that it can be held in any one of several positions bymeans of locking screw 28 engaging one or the other of re-' cesses' 29, 29, 30, or 31. (See Figs. 4 to 7 inclusive.) As shown in Fig. 2, the screw 28 engages recess 31-, and in this position, applying transverse stress to thehandle 13 in the unlocking direction, will bring it. to

the position shown in Fig. 2 where the handle Fig. 2. In this situation, the sliding jaw 4 ratcheting stress,

is entirely unlocked and may be moved freely in either direction, with or against the pressure of spring 21. It may be retained against said pressure by a finger or thumb of the user engaging lugs 4 or 4, which are provided for this purpose.

Whenthe direction of pressure on handle 13 is reversed, however, the handle will come in solid contact with surface 30 of shank 5, in the position shown in Fig. 1. In this position, the cam surface 15 permits retreat of pilot screw 7 under the influence of spring 21, with the result that the locking thread 1 immediately engages rack teeth 2, as shown in said Fig. 1.

This results in a monkey wrench wherein pressure applied to the handle toward the left will-lock the slidingjaw 4, as shown in Fig. 1, while pressure toward the right W1llrelease the sliding jaw, as shown in Fig. 2. Thus the jaws will automatically ratchet around the head of a bolt or nut in response to the screwing and resetting pressures. The lighter'the spring 21, the lighter will be the but the slower will, be the reseating of the jaws; but in general a light spring is desirable and in pract ce 1ts. l1ghtness will be limited by the welght of aw 4.

Hence this part may desirably be made of duralumin or similar aluminum alloy As it is desired to make the locked position the normal position, I provide a bell crank lever 31, mounted on-pivot 32' and tensioned in the proper direction by spring 33. It Wlll be remembered that in this normal locked p0- a The unlocked posi sition, the worm sleeve 3 maybe adjusted by hand operation after the manner of the ordinary monkey' wrench.

'tion'of cam plug 25is shown in-Fig. 4, and the locked position in Figs. 2 and '7. Said plug 25 is rotatably mounted and the lockingscrew 28 is pro .vided for the purpose of permitting adjustmains in the lowermost position no matter which way the handle is stressed. In the latter position the jaw 4' may be adjusted by hand rotation of worm 3', as above described.

The various positions of camplug 25 may v be exteriorly indicated by a pointer 25".

The main function, so far as above described, would be performed, even if sleeves 10 and 3 were integral. An important feature, however, is making them separate and splining sleeve 3 on sleeve 10, as above described. In the specific arrangement shown in Fig. 2, the inner or pilot sleeve 10 is rovided with ball bearings to eliminate rictional resistance to rotation. The n per bearing is aiforded by ball 35, in race 36, aving an internal retaining lip 37, the function of which latter is mainly to prevent the balls from falling out, particularly while the parts are being assembled. The lower bearings comprise balls 38 in a similar race in the lower end of the sleeve 10, the other bearin surface for the lower balls being the annu us 23 previously mentioned. Obviously, if thesleeve 10 were integral with lockin sleeve'3, theseballs would have to take\the ull thrust of the maximum strains that can be applied on the slidin jaw- 4 and in practice these strains WOIIIdTJB likely to exceed the crushing resistance of any balls suitable for use in such a position. Hence one feature of invention and advantage involved in making the locking sleeve 3 capable of slight longitudinal movement with respect to pilot sleeve 10, is that it permits the solid thrust surface 4 to take the load and relieve the balls of allload. An incidental advantage is that the friction ofsurface 4 at the end of sleeve 3 becomes available as part of the friction lock factor, making it possible to use a lockingthread-l of steeper pitch than would otherwise be possible; this in turn making it easier to. get a slip angle pilot screw of the samepitch as the locking thread. I

' The spline connection 11, 12, leaves the sliding jaw 4 and the inner pilot sleeve 10 free for a slight endwise movement with respect to the outer locking sleeve 3, when the pilot'thread 8 rotates the locking threadl', into or out of its. frictional end-thrust engagement with surface 4 on the slidingj aw 4. Upon locking,

when the pilot screw 8 retreats endwise, its

upon further rotation the spline permits thelocking thread to take out is own back-lash by screwing iself along the rack 2, into firm engagement with surface 4 on said sliding j aw 4, thereby affording a solid path of thrust from the sliding jaw through the outer or locking sleeve and thread, to the relatively stationary rack, without endwise stress upon the inner sleeve.

V Vhcn the retreat of the pilot screw is by spring pressure, the automatic elimination of all back-lash presupposes a spring strong enough to do the work, which may not be necessary or desirable, in certain cases. Preferably the clearance between pilot thread elements 8 and 9, that is, back-lash or looseness of fit measured lengthwise of the pilot screw, is less than the clearancebetween the locking thread elements 1 and 2, in which case the pilot screw will take the load and will permit free sliding of the jaw 4 in both directions. As considerable back-lash is unavoidable in the pilot screw because of the acuteness of angle along which back-lash is measured, I prefer to make the pilot screw back-lash or clearance as small as practicable and make the locking thread clearance relatively great. Fortunately the permissible margin for this is ample since the spaces between rack teeth 2 may be out very wide before there is danger of weakening them below the maximum load limit.

In certain cases, however, it may be desirable to make the pilot screw clearance greater than the locking screw clearance, in which case the pilot thread groove can have only one of its working surfaces in position to take load and unlock the locking screw. In such case, the pilot screw may be held to a midway position where it is inoperative and the looking screw locks against thrust in both'. directions; or by shifting one way or the other,

there will be sliding in one direction and lock in the other, but there is no position permitting free sliding in both directions.

The inner sleeve 10 is held in axial alignment with its thrust hearing by sleeve 3 of which a reduced portion 40 has sliding fit within a recess in sliding jaw 4. At the other end sleeve 3 has an interior bearing 41 on nippic 24 and a washer 42 prevents longitudinal displacement of the reduced portion 40 out of its bearing.

In all of the foregoing, the pilot screw never has to sustain any important endwise thrust; hence it can bemade quite small, to give a high' pitch to its thread on a limited predetermined number of turns per inch.

Nevertheless, in practice, it may be desirable to cut the pilot groove quite close to the axis,

in order to get the desired easy slip angle,

fer to-cmploy a pilot screw of substantial diameter and form the pilot thread as a groove ,cut in as close to the aXis as may be neces sary for the purpose in view, the outer portion of the groove being cut away as at 8", so that only the inner a screw thread.

The pilot screw 7 and encircling spring 21 are preferably protected by tube 44, rigidly screwed to the sliding jaw bracket 4 and having loose sliding fit in filler piece 45, secured in handle 13 by lugs 46.

\Vhile the various details of my invention above-describcd as embodied in this type of monkey wrench are novel and are of considerable practical importance, all except the more basic features of function and construction are capable of wide variation as will be evident from the forms hereinafter described. In some of these the similar shapes and structures will be obvious while in others they are shifted about and combined with new elements making identifications more difiicult.

In Figs. 8, 9. and 10, the broad essentials of the invention are applied to another form of monkey wrench; the external appearance is that of another well-known commercial form. The basic elements and their cooper-- ating functions are essentially identical with those just described in detail in connection with Figs. 1 to 7. In so'far as concerns ge-' neric features, and except for the differences which I will now 'describe, the preceding general statements with reference to my first described form of wrench may be taken as applying to the various embodiments described hereafter.

In Fig. '8 the similar basic elements are the locking threads 51 on rotatable sleeve 53, and the locking thread element 52 on a member which is longitudinally movable with respect to the sleeve; also the pilot screw 57 with slip-angle groove 58, engaging interior slip-thread elements in said rotatable sleeve 53; also the spring 71 which has the double function of pressing the lower jaw 54 tothe closed position and also forcing the pilot screw to inoperative position when the endwise thrust of the operating cam is removed. The shank 55, integral fixed jaw 56 and the sliding jaw 54, with strap or loop members for retaining it in engagement with shank 55, will also be recognized. An important practical difference is that the handle is solid, has no oscillating movement, and may be shaped precisely according to the old standardized designs. In Fig. 8,. the rotate ing locking-screw element 51, 53, is now associated with the fixed jaw and shank 55, being portion 8 functions as 54, and retained against withdrawal by suitable surface on the slidable jaw at 84.

the furtlier efiect of pressinglbthe slidable knurled flange element 54, extending under projection 54 onshank 55. Thisrotatable locking screw element 51, 58, is elongated to the full length of the throw of the slidable jaw 54, while the non-rotatable locking screw element 52 is short, just the reverse of the length relations of the rack 2 and the worm '1 in Figs. 1 and 2; and said rotary locking element 51, 53, is now'associated with and carried by the sliding jaw element. Said pilot screw 57 is held from rotation while being permitted the requiredgl longitudinal movement by a guide sleeve 72,. having a slot 7O engaged by spline pin 69flwhich passes through the rear end of the pilot screw. The sleeve 72 is screw threaded intothe sliding j aw, and is locked in place by key screw 68.

The handle being rigid in' Fig. 8, other movable means must be provided for giving the pilot screw 57 the required endwise shift to throw it into looking or unlocking position. The cam surface 65 for performing this function is formed on a separate jawface element 80, the upper face of which forms the work-engaging face of the sliding jaw. This supplemental, working-face element of thesliding jaw is preferably the full width of the jaw. It is knurled at the sides as at 81 to afford a good holding grip whereby it maybe moved transversely by hand to throw the cam surface 65 into and outiof displacing position at the rear end of the pilot screw 57. The slidable face piece 80- is formed with a dove-tailed portion 82 depending into a correspondingly shaped recess in the sliding jaw. The face piece, being inserted in the sliding jaw before assembling,

is then safe from sliding out at the front. The slidable face piece is also provided Wlth ife a recess.83 for holding one end of a thrust spring 85, the end of which butts against a The spring 71 bears at one endon the bot'- tom of recess 71 in the handle of the wrench and at the other end upon a collar 86 swivelled on the end of pilot screw 57. The pressure. of the spring on this-collar has the primary effect of forcing the pilot screw as far back as the cam will let it go and thereafter jaw to the closed position. viously, the slidable face piece 80 maybe pulled out or pushed in by hand the distance necessary to give the endwise cam thrust and retreat of the pilot screw 57, which will put it into and out of unlocking relation with the locking screw 51.

There is, however, a further and more important capability of operation. When the jaws are open and a nut of ordinary dimensions is clamped between them, with its centreat a pointindicated as at C, Fig. 8; then a rotary efl'ort on the handle in the direction of the arrow B will give a stress on slidable face piece 80 in the direction of arrow S, the horizontal component of which, as indicated by arrow M, tends to force such slidable element to the right moving cam 65 in the direction for releasing and permittingretreat of the pilot screw 57, to the inoperative position, thereby. causing the locking thread 51 to lock the sliding jaw against opening. Reverse pressure, however, applies a reverse sliding component to face piece 80, forci cam 65 under the pilot screw 57, thereby thrusting-the latter downward to cause roever wedging action there is by the pilot screw 57 under the pressure of screw 71, affords a further pressure in the same direction. Under certain conditions, however, a tension spring such as the spring 185 of Fig. 11 may be substituted for the spring in which instance, it would be easier for the jaw 80 to slide outward and overcome the excess pressure of spring 71 and the bed of the face piece 80 would be slightly inclined to give said face piece a pressure responsive bias toward either the locked or unlocked position of the same.

For convenience in manufacture and assembly, and also for the functional advantages', the jaw 56 and shank 55 may be "in; tegral, the lower portion 55 being shaped to fit the hand. Portions 55, 55*,iwill be small enough to pass-through the straps54, 54",

of the sliding jaw, which latter will be applied thereover after the face piece 80, with backing spring 85, have been inserted therein from the rear. The locking screw sleeve 53 may be then screwed into 52 just far enough to give the member 54 a loose fit against 54 when. the jaws are closed. Thereupon'the supplemental handle section 55 is applied and secured by screw bolts'55 The section '55 is additionally secured against the endwise strain by means of the endwise thrust shoulder 55.

It will be noted that in this device the locking sleeve 53 takes the entire endwise rigid-handle embodiment of my inventionas applied to an 8 type wrench, wherein the jaw opening is presented outwardly endwise of the handle. In this form, certain features are so substantially like; some of the parts in Fig. 2 that I have given them the same nu- -merals, while others are similar in function more than in form. The locking threads 1 are on theexterior of asleeve 3 which is movable longitudinally but not circumferentially on inner sleeve 10, having interior' pilot screw elements 9, the, driving connection belng through sphne screw 11, engaging spline groove 12. In the present form,

' connection with'Fig. 2. The pilot screw 107 has the same functions as in both the preceding forms while the sliding jaw piece 180 carries a cam surface 125, adapted to endwise shift the pilot screw to release the locking thread l. There isals'o a spring 121 tending to close the movable jaw 104 against the fixed jaw 106, and also to thrust the pilot screw against the slidable cam surface 125.

The pilot screw element 107 is function,-

ally associated with the slidable jaw and its' endwise movement is controlled by and from said jaw, although said pilot screw element is actually housed in the fixed jaw member.

This is made possible by use of a pilot screw rod or extension member 127, slidably mounted in the sliding j aw. 104, and having a depending portion 128, the lower end of which is secured to the rear end of the pilot screw element, preferably by pivot 129. The device further differs from any of the receding in that the rack 102 is on the slidable Because of the transverse disposition of the moving parts, the spring 121 for holdlng the pilot screw extension 127 against the cam 125 is curved around an anti-friction roller 130 and extends down into a tubular cavity 131 in the handle. The face piece 180 of the slidable jaw is normally pressed outward with its cam element 125 in contact with the cam 126 of the pilot rod by means of a contractile spring 185. In this case the spring 185 acts in opposition to spring 121 in contrast to the arrangement in Fig.8, wherein spring acts in harmony with spring 71. Consequently spring 185 must be substantially weaker than spring 121, and its purpose is to make the face piece 180 more sensitive to unlocking efforts.

In Fig. 11, as in Fig. 8, the'locking screw can always be rotated by hand even when thepilot screw is in the position for locking.

. In all the forms shown in the Figs. 1 to 13, inclusive, the strength, proportion and arrangement of the parts is designed with a view to performing the unlocking operation at a time when the load is removed or min-' imized on the sliding jaw, as by relief or reversal of pressure on the handle. The broad principles of my'invention, however, are applicable to devices wherein the load on the ber, that is, a member corresponding to the rack in Figs. 1, 2 and 11 and corresponding to the thread 52 in Fig. 8.

The conditions of heavy, continuous load, and necessity for release under load, are found in lifting jacks, illustrative examples of which, embodying'my invention, are found in Figs. 14 to 17 inclusive.

In Figs. 14 and 15, the outer load screw of the jack is the relatively rotatable and longicomprises the locking thread 201 on the outside of the tubular sleeve 203. The co-op'erating, normally stationary, locking screw thread 202 is longitudinally fixed with reference to the stationary. casing 205, but, for a purpose described below, it is formed on a separate sleeve member 205 supported by shoulder 205 and held in position by a screw 205 engaging circumferential recess 205 which permits slight rotary movement of the locking thread 202 with respect to casing 205. Thepilot screw 207,- having a pilot groove 208, is fixed against both longitudinal and circumferential movement by a pin 208*, keying it to'base 205, which is secured to stand ard 205 by bolts, as at 205. The co-operating pilot thread element 209 is on the inner face of an inner tube or sleeve 210, which is rigid ly connected to locking screw sleeve 203 through cap plate 236 to which pilot sleeve 210 is secured by key 237 andlocking sleeve 203 by dowel pin 212. Thus the outer locking screw sleeve 203 and the inner pilot tube sleeve 210 revolve and lift as a solid unit.

In order -to rotate this unit .to screw up the load, there is an innerdriving tube 238, secured to bevel gear 239 by key 240. -Gear 239 is journalled 'on an enlargement 241 on the base of the pilot screw 207 and is itself driven by pinion 241 which is, referably, arranged at a slight angleto the; orizontal, and is journalled in casing 205,, as at 242. It isheld from endwise'moveme'nt by collar 243, secured by key pin 244.; The outer end of 245 is squared so that an extensible socket handle can be applied, removed and operated without the necessity for the operator to stoop, the inclination of the pinion axis be- 90- tudinally movable locking screw element." It w I the operator.

When the pinion and gear are thus rotated, and thereby the driving tube 238, the rotary movement is imparted to the locking screw through spline key 246 which has a sliding fit in groove 247 in said tube 238.

In this lifting jack, as in the preceding device, the pitchangle of the locking screw thread is such that the thread friction under load, plus the other resistances to rotation,

affords prohibitive resistance to any automatic unscrewing of the locking thread by pressure of the'load. In this'case also, as in the others, the pilot thread has the same number of turns per unit length as the locking thread and hasa steep slip angle, so that it easily rotates innerfpilot sleeve 210, cap plate 236, andouter locking sleeve 203.

.In the present case, the clearance space in the groove of the pilot screw element is greater than the clearance space between the threads of the locking screw element,'instea'd of being less, and the desired shift of load from the locking threads of the pilot threads is accomplished by rotating sleeve 205. The means for rotating and-locking the sleeve 205. in various positions is a handle 247 pivotcd at 248 in ears'249, on said sleeve. ,The handle is formed with a locking projection 250 adapted to engage a suitable recess 25 for locking the sleeve in the midway position where the pilot screw is totallyinoperative because its clearance is'greater than that of the locking threads. The other two positions will be circumferentially distant from 251 by the amount requiredfor advancing or backing threads'202 to the positions required for shifting to and from the pilot screw, either the up-pressure of spring 221 or down-pmssure of a load being supported by the jack.

There are three characteristic positions for the sleeve 205.

First, the one shown in the drawings where the locking projection 250 is in recess 251 and the locking threads 201 have their top surfaces in contact with the bottom surfaces 0 threads 202, being thrust thereagaihst by spring 221, but the pilot groove threads are not in contact because of the above-described greater clearance or looseness. of fit of the latter. If load be applied to the topof the jack as by. rotating the gears in the properidimotion, the result will be to shift threads 201 downward so as to bring their lower surfaces in thrust relation to the tops of threads 202, but pilot projections 209 will still be out of contact with. the bottom faces of the pilot grooves. In other words, the pilot screw'is wholly inoperative as regards any thrust, whether upward or downward. Consequently, the jack is automatically held in the collapsed position against the thrust of the powerful spring 221, and attbe sans: time is free to be screwed up or down by means of the gears.

Second, he position, of "the sleeve 205", wherein its rotation has screwed upward and lifted sleeve 2'03 and through it the pilot groove screwing the locking threads at the rate necessary to permit this. This brings the ack instantly under the load-and return of the handle to the first position will permit lifting the load by rotating thegears, as above described.

Third, rotating sleeve 205 to back off the thread 202 from support of thread 201 thereby lowering the locking sleeve and through it the pilot sleeve to the extent necessary to make pilot threads 209 come into contact with, and apply thrust upon, the bottom of the pilot groove, thereby slipping therein and rotating the locking sleeveto automatically screw the locking threads 201'downward. Such downward screwingwill be at a speedproportional to the completeness with which the locking. 1

threads have been relieved of the load and-the pilot threads have taken load. Thus the handle 247. may be used as a throttle to lower the load slowly or rapidly or intermittently.

The practical effects of this mechanism are to produce a jack which can be placed in aposition under a load to be lifted and by a simple operation of the lever, the jack can be caused to automatically jump to a position directly in contact with the load so that the'first operative movement will immediately result in .a

lifting action. Throughout the range of lift,

the jack operates as an ordinary jack. When it is desired to lower the load, the jack can be I automatically transformed from an'absolute load retaining mechanism 'to a collapsible mechanism, collapsible under the action of the load itself. At all times, the lowering of.

the load-is under absolute control of the 0 ,erator as regards speed or distance, since t e load, eventhough in downwardknotion, may

be stoppedat'any desired point... Another feature is that the loadfretaining threads themselves act 'asa brake. 1 In order that the screw structure may rojtate easily under load, I provide a pressure cap 252 and interposed ball bearings. 253.1

The cap 252 preferably has its upper surface roughened to prevent the load from tending to slip at any time. The ball thrust hearing is enclosed in thedirt proof-chamber formed in the interior of cap 252, the latter being secured by screw254engaging groove 255. It should be noted that the screw sleeve 203 and cappie'ce 236, as an upper rotating and sliding element, and-bevel gear 239 and drivon the pilot screw when lowering.

ing tube 238 as a lower rotating element, .form a pocket whose upper and lower surfaces revolve at the same rate of speed but whose length changes as the load is lifted. This pocket contains the heavy thrust spring 221.

The ball bearings minimize the torque load Hence thelatter may be of smaller size and will slip with less pitch angle.

In the modified forms of lifting jacks shown in Figs. 16 and 17 are found practically all of the important functions described above in connection with Figs. 14 and 15, including the rotary adjustment of the normally stationary locking screw element to the characteristic three positions whereby the pilot screw may be rendered entirely inoperative, or operative in the up-direction under the impulsion of the heavy internal spring, or in the downward direction under the impulsion of the load. These features are embodied in practically the same number and kind of operating-elements, but the heavy. external casing and the bevel gears and the driving tube 238 have been dlspensed with and a ratchet has been substituted at the hand screwing means.

The load bearing cap swivelled on ball bearings requires no description. The con nection of the exterior locking sleeve 303 with the internal pilot sleeve 310, through cappiece 336, pin 312, and key 337, are substantially the same as in Fig. 14. The structural arrangement and disposition of the operating elements involve important features of novtil elty and advantage.

The locking thread 301 is on the inside of sleeve 303 and the co-operating locking threads 302 are on the outside of a tubular member 305", which, instead of being short like the corresponding part 205, in Fig. 14, extends down to the base of the machine and constitutes in effect the stationary standard of the jack, surrounded and protected by the sleeve 303. This arrangement is obviously neater and affords better protection of the screw threads from injury and from dirt.

The said member 305 is rotatably mounted onthe stub standard 305, which is integral with-base 305. It hasan ample thrust bearing for carrying the load at 305 and is secured against withdrawal by pivot screws 349, fitting annular groove 305. The means for rotating sleeve 305 to the three characteristic'positions above described consist of a fork 348, pivoted at 349 and provided with a socket 350 for insertion of an operating handle. The locking in the operating'position is by engaging of the socket member in a recess for betweenlugs indicated in dotted lines at 351.

The rotation of the locking thread 301, by hand, to lift the load, is by means of a ratchet applied to the exterior of sleeve 303 which is 421, engaging bracket 422, on base 405.

this form the clearance of the pilot-screw formed with a circumferentially disposed series of ratchet teeth 352. The ratchet housing 353 is supported by engagement with the tops of the ratchet teeth as at 354, and is prevented from upward displacement by split spring ring 355, sprung into groove 356. The ratchet pawl 360, pressed forward by spring 361, is slidably mounted in a shell 362 which is, in turn, slidably mounted in an opening 364, intersecting the ratchet cavity at right angles. The shell 362 and the pawl carried thereby are normall pressed outward to inoperative position y spring 366 engaging head 367. The pawl is rotatably mounted in shell 362, but is normally held with its operating face 368 parallel with the ratchet teeth by pin 369, engaging groove 370. The rear of the pawl is provided with a knurled extension 371, whereby the direction of its working face and the resulting ratcheting operathe operating bar or lever through transverse opening 372. The bar opening 37 3 through the pawl is enough larger than the bar opening through the shell to permit of the necessary reciprocation of the pawl without interference by the bar. An advantage of this construction is that when the bar is withdrawn and the releasing fork operated to permit the jack to run down under pressure of the load, the pawl being automatically disengaged, the shell 362 does not have to rotate with the ratchet teeth and hence is not dangerous when lowering the load at high speed. In Figs. 18 and 19, I have shown a device in which theessential elements of the invention are embodied somewhat differently from any of'the preceding. The exterior appearance of the vise is more or less conventional, comprising a fixed jaw 404, integral with base 405, and a movable jaw 406, having a shank 406%, which is longitudinally slidable with respect to the fixed jaw and slidably held by the encircling portion 404. V l The locking thread 401 and the pilot thread 408 are in the samegrooveof a single screw 478. The cooperating locking screw element 402 is a shallow thread integral with the fixed base 405 and is analogous to the rack 2 0n shank 5 of Figs. 1 and '2. The co-operating pilot screw element 409 is a deep thread on the interior of nut 410, which latter is capable of slight longitudinal movement with reference to locking screw element 402, being supported by longitudinal bolts 410 and .410", slidably engaging the portion 403- of base 405, and normally tensioned rearwardly by sprilIig threads is small, much smaller than the clearance of the locking screw threads which latter have substantial clearance for a reason explained below.

The feature of having a locking screw and pilot screw made in one piece depends on the 5 principle that, as an screw thread is cut deeper, the an 1e of inclination toward the centre will be ar greater than the angle of the outer periphery, even though the pitch be the same. 'Advantage-of this is taken by using the outer peripheryas a locking angle and the inner portion as the slip angle. In the construction of the vise, since the locking screw is a tension member, it is more practicable to use such a construction than where the screw member is used in compression; be-

cause a tensile stress will always tend to keep a screw straight, whereas a compression stress would have a tendency to bend it. The forward end of the screw member 47 8 rotates in a double thrust ball bearing 425, the inner race of which is heldrigidly to the screw by a threaded nut 430, which, in turn, is

immovably locked to the screw b pin 431.

The outer race collar of this ball earin is slidably mounted in the sliding j aw mem er 406 between thrust disc 432 on one side and the spring 433 on the other side. The operating handle 434 for the vise is on a loosely rotatable hub-member, 435, which has turned In it a ring groove 436, engaged by a pin 437, which permits rotation but limits its axial movement at all times. The inner face of the hub is formed with jaw clutch projections 438 adapted to be moved into and out of enas gagement with co-operating clutch projec tions on the threaded nut 430, which is pinne on the end of the screw 478.

In operation the handle 434 would be pulled forward. This would transmit the pull through the pin 437 to'the sliding jaw. The sliding jaw would then transm t this pull through the sprin 433 to the ball bearing 425 which is mounte on the locking jaw, and thereby to the screw 478. a j

I The outer or locking thread element 4010f the screw is normally free from locking engagement with the locking thread element 402, but the inner periphery or slip angle thread is in engagement with the pilot nut 410,.which ma move forward. The forward pull on the pi otnut is resisted by the spring 421. Spring 421 holds theipilot nut back hard enough so that when the screw 478 has been pulled the slight distancenecessary to then pushed backwar free locking threads 401,402, (as in Fig. 19)

is inserted between the jaws, the sliding jaw 406 may be pushed backward until the jaws close on the. work. C(perating handle 434 is the jaw clutches 438 on the hub 435, and on 430, are caused to engage and rotation of the handle 434 will then cause corresponding rotation of the locking screw member 47 8. The first eifectof this rotation will be to rotate the screw member '47 8 on the pilot nut 410 as a base until the clearance between the rear of clutch-member 430 and the front of thrust disc 432 on the sliding jaw is taken up. Further rotation will cause locking screw element 401 to contactwith the stationary screw element 402, take out the slight clearance in the threads at this point and then tighten the jaws of the vise on the work with a non-releasable grip. While this non-releasable grip is bein applied the pilot nut 410 is fed forward y the slip screw thread and against the pull of spring 421, but the clearance provided between the forward face of the ilot nut 410 and the rear face of stationary e ement 403, is suflicient to prevent the pilot nut from jamming the stationary When the work to be clamped by the vise nut. In this operation, also, the ball bearing is loaded only with the reslstance of spring 433, and we have helping us in the locking stage both the friction of the locking threads and the friction of the rear face of jaw clutch member 430, on the front face of thrust disc at the surface where there was previously a clearance.

The pilot nut 410 is itself slidably guidedto the stationary nut 403 by means of the screws 410 and Its backward position is lim ited by the length of said screws. The locking screw thread 401 issubstantially clear of radial frictional resistance when pull is being exerted on screw 47 8 through handle 434; the resistance to rotation being then comprised only of the inertia of the moving parts, the ball bearing resistance'and the frictional resistance in the pilot nut itself. Hence only a very small axial force need be applied to cause the sliding jaw to slide either in or out. This construction allows the vise to present an external appearance which is practically identical with that of existing types.

In this application I havedescribed the I member at a definite rate of speed and means for positively shifting the phase relation of the locking, pilotmembers whereby the de or different forms of locking members, preferably toothed, and a different form of pilot mechanlsm which may include toothed gearing of the proper size, chain belts, or other positive-ratio, motion-transmitting mecha-- nism. Such combinations are perhaps more applicable to the field of change gear mechanisms, variable intermittent mechanisms, stepless ratchets, and specific disclosures as to these are reserved for an application or applications about to be filed.

Many of the following claims are broad enough to cover the embodiments of the invention shown in all of the figures of the drawing and the variety of the forms helps to emphasize their broad scope. The remaining claims, some of them quite specifically, are all readable on theform of the invention shown in Figs. 1 and 2. Specific claims for the more specific novelty of the embodiments shown in Figs..8 to 19 will be presented in the divisional applications about to be filed.

I claim:

1. In releasable thrust mechanism, continreceiving elements are moving in the direction of the thrust.

2. A thrust-receiving member mounted for movement in the direction of the thrust and a support therefor locking by friction against yield in the direction of the thrust, in combination with a pilot mechanism including an element shiftable to relieve frictional locking resistance, and means for utilizing thrust applied by said thrust-receiving member, to

drive the relieved locking support element in the direction of thrust applied by said thrust-receiving member, at the rate required to prevent re-locking.

3. A thrust-receiving member mounted for movement in the direction of the thrust and a locking. support therefor, in combination with a pilot mechanism including an element shiftable to unlock said locking support, and means for utilizing. thrust applied by said first member, to, drive said locking support in the direction of thrust applied by said thrustreceiving member.

4. In releasable thrust mechanism, continuously intermeshed thrust-supporting elements which, in the direction'of the thrust, are in reciprocal thrust relation and normally lockedagainst movement in response to thrust, in combination with shiftable pilot mechanism for relatively moving the thrust elements to relieve locking engagement and for then causing relative movement of the relieved locking elements through distances and at rates necessary to maintain the thrustrelief relation, while the parts are moving under thrust applied in either direction.

5. Releasable thrust mechanism including toothed thrust-supporting members having backlash upon reversal of thrust and normal-.

1y locking by friction when the backlash is taken up, in combination with shiftable pilot mechanism for relatively moving such -members in the direction to relieve thrust pressure on their frictional locking surfaces and for then driving them at the rate required to maintain such relief while the parts are moving under the thrust.

6. In releasable thrust mechanism, toothed thrust-supporting members which, in the direction of the thrust, are continuously in mesh but with clearance aifording backlash upon reversal of thrust and normally locking by friction when the backlash is taken up, in combination with shiftable pilot mechanism for relatively moving such members in the direction of said clearance to relieve thrust pressure on the, frictional locking surfaces and for then driving the relieved toothed member atthe rate required tomaintain such relief while the parts are moving in the direction of the thrust.

7. In releasable thrust mechanism, toothed thrust-supporting members which, in the direction of the thrust, are in reciprocal thrust receiving and transmitting relation but with clearance alfordingback lash upon reversal of thrust and normally locking by frictional engagement when the back lash is taken up in either. direction, in combination with shiftable pilot mechanism for relatively moving such members to afford clearance between the thrust transmitting and receiving surfaces in both directions, and for thendriving the relieved toothed member at the rate required to maintain such relief while the parts' are moving under thrust applied in either direction.

8. A thrust-receiving member mounted for movement in the direction'of the thrust and 'a locking support therefor, in combination with a pilot mechanism separate from said thrust receiving member including an element shiftableto unlock said "locking support, and means for utilizing thrust applied by said thrust-receiving member, to drive said locking support element in the direction of thrust applied by said thrust-receiving member.

9. A thrust-receiving member mounted for movement in the direction of the thrust and a support therefor lockingby friction against yield inthe direction of the thrust, in combi-' nation with a pilot mechanism including an element shiftable to relieve frictional locking resistance, and means for utilizing thrust applied by said thrust-receiving member, to

- drive the relieved locking support element for movement in the. direction of the thrust and a lock screw support therefor, in combination with a pilot screw mechanism including an element shiftable to unlock said looking screw, and means for utilizing thrust applied by said thrust-receiving member, to rotate one of thelock screw elements to permit movement in the direction of thrust applied by said thrust-receiving member;

11. A. thrust-receiving member mounted for movement in the direction of the thrust and a locking screw therefor, in combination with a pilot screw mechanism including anelement shit-table to unlock said locking screw and a slip-angle thread for utilizing thrust appliedby'said thrust-receiving member, to drive said locking support element in either direction at the rate necessary to prevent relocking.

12. In releasable thrust mechanism, screw elements mounted for relative rotary screwtherefrom slip thread elements, all having the ing movement in thrust'relation, but with backlash in the direction of thrust, and cou pled thereto, pilot mechanism adapted to relieve thrust on said screw elements and utilize the same to produce relative movement in the direction of the thrust.

13. Releasable thrust mechanism including continuously meshing screw members which, in thedirection of the thrust, are in thrust relation but with clearance aiiording backlash upon the reversal of thrust and normally locking by frictional engagement when the backlash is takenup in either direction, in combination with pilot mecha- "'nism including a pilot screw having the same lead but of smaller pitch diameter so as to permit slip and rotation under thrust, and means for endwise shifting the pilot screw to cause and utilize such rotation to rotate a locking screw element in a direction to relieve pressures onthelocking threads and for thenautomatically screwing said locking thread member at the rate required to maintain such pressure relief, while the partsare moving under load. v

14. A relatively fixed support, a thrustreceiving member mounted for movement with respect thereto, and lock screw elements for locking said member to said support, in combination with pilot screw elements having a slip angle thread, all threads having the same lead and the rotating elements of the lock screw and slip screw being coupled in reciprocal rotary driving relation, in combination with means producing movement of said coupled parts and shifting. thrust from and to the slipangle thread for the purpose described,

15. A relatively fixed supp0rt,-a thrust receiving member mounted for movement with respect thereto, and lock screw elements for locking said member to saidsupport, in combination with pilot screw elements having'a slip'angle thread, all threads having the same lead andv the rotating elements of the lock'screw and slip screw being concentric sleeves splined together in reciprocal rotary driving relation, but with the locking sleeve free for 'endwise movement to take locking position without stress on the slip sleeve, in

combination with means, producing relative v same lead, the rotary thread elements of both being associated in reciprocal rotary driving relation and the sli thread having less back lash than the locking thread, whereby the slip thread elements may be relatively moved in position to take load in both directionsand, upon slip movement under load, to rotate a locking thread element with the locking threads out of locking contact-with each other.

18. A relatively fixed support, a thrustreceiving member slidably mounted thereon, a locking screw element on the fixed support parallel with the movement of the thrustreceiving member, a slip thread element on the same support and parallel with said lock thread element, co-operating slip thread and lock thread elements on said thrust-receiving member associated in reciprocal rotary driving relation and both in position to take the thrust of the thrust-receiving element, and the threads of said slip elements and locking elements having' the same lead, in combination with' selectively operating means for causing either the sli threads or the locking threads to take said t rust.

19. A relatively fixed support, a thrustreceiving member slidably mounted thereon, a locking screw element on the fixed support parallel with the movement of the thrustreceiving member, a slip thread element on the same support and-parallel with said lock screw element, co operating slip thread and lock thread elements'on said thrust-receiving member associated in'reciprocal rotary driving relation and both'in position totake the thrust of the thrust-receiving element, and

the threads of said slip elements and locking element rotating therewith, said locking means having its locking threads continuously in mesh with, but loosely fitting between the teeth of the rack, in combination with a pilot screw having a slip thread co-axial with said locking threads and engaging the slip thread element rotating with said locking worm, the slipand lock-threads having the same lead.

21 A guide member having a rack, a thrust-receiving member slidably mounted on said guide member for movement parallel with the rack, a locking worm rotatably mounted on the slidable member, a slip thread element rotating therewith, said locking means having its locking threads continuously inmesh with, but loosely fitting between the teeth of the rack, in combination with a pilot screw having a slip thread co-axial with said locking threads and engaging the slip thread element rotating with said locking worm, the slipand lock-threads having the same lead, and means for moving the slip screw endwise to cause it-to receive. thrust from the thrustreceiving member.

22. The combination specified by claim 20, w th means for moving the slip thread endwlse to rotate the locking worm thread out of locking engagement with the rack, and to a position where movement of the released thrust receiving member in either direction will cause the rotary slip thread element to rotate and thereby rotate the locking thread gleplilent without re-engagement with the rack A relatively fixed support, a thrust-receiving member mounted for movement with respect thereto, and lock screw elements for locking said member to said support, in combination with pilot screw elements having a slip angle thread, all threads having the same lead; rotating elements of the lock screw and slip screw being concentric sleeves splined together in reciprocal rotary driving relation to permit relative endwise movement and afford independent paths for the end-thrust thereon, one path through the locking sleeve and thread,-and another through the slip sleeve and the slip screw; in combination with means for endwise shifting the slip screw to shift thrust from the locking sleeve path -to the slip sleeve path.

24. A relativelyfixed support, a thrustreceiving member mounted for movement with respect thereto, and lock screw elements thrust thereon, one path through the locking sleeve and thread, and another through the slip sleeve and the slip screw, and the locking sleeve having more end playthan the slip sleeve; in combination with means for endwise shifting the slip screw to shift thrust from the locking sleeve path to the slip sleeve path.

' 25. A relatively fixed support, a thrust-receiving member mounted for movement with respect thereto, and lock screw elements for locking said member to said support, in combination with pilot screw elements having a slip angle thread, all threads having the same lead; rotating elements of the lock screw and slip screw being concentric sleeves splined together in reciprocal rotary driving relation to permit relative endwise movement and afford independent paths for the end-thrust thereon, one path through the locking sleeve and thread, and another through the slip sleeve and the slip screw, and the locking sleeve having more end play and its threads more back lash than the slip sleeve 4 and thread; in combination with means for endwise shifting the slip screw to shift thrust from the locking sleeve path to the slip sleeve path.

26. A relatively fixed support, a thrustreceiving member mounted for movement with respect thereto, and lock screw elements for locking said member to said support, in combination with pilot screw elements having a slip angle thread,-all threads having the same lead; rotating elements of the lock screw and slip screw being concentric sleeves splined together in reciprocal rotary driving relation to permit relative endwise movement and afi'ord independent paths for the endthrust thereon, one path through the locking slip sleeve and the slip screw, and the looking sleeve having more end play and its threads more backlash than the slip sleeve and thread; in combination with means for endwise shifting the slip screw to shift thrust from the locking sleeve path to the slip sleeve path; together with means for pressing the thrust-receiving member toward the direction of the working thrust.

27 A load receiving screw element threaded to two other screw elements, having the same rate of screw feed but having different pitch diameters so that their stresses and mo-- tion producing tendencies with respect to said load are different.

28. rotary screw element threadedto two sleeve and thread, and another through the. in

other zoo-axial screw elements, havin the same rate of screw feed but having di erent pitch diameters such that one is a locking.

screw thread and the other a slip screw thread, in combination with means for shifting the phase relations of the threads to shift thrust from one thread to the other for thepurpose described.

- 29. In releasable thrust mechanism, screw elements mounted for relative. rotary screwing movement in reciprocal thrust relation, but with backlash in the direction of thrust, and pilot mechanism adapted to relieve thrust on said screw elements and utilize the same to produce relative movement in the direction of the thrust, in combination with a shiftable' element operable by exterior force in opposition to said thrust and shifting upon reversal of direction of the stress thereon, and means for utilizing such shifting movement to put the pilot mechanism into and out of relation for the above-described operation.

30. In releasable thrust mechanism, screw elements mounted for relative rotary screwing movement in reciprocal thrust relation, but with backlash in the direction of thrust, and pilot mechanism'adapted to relieve thrust on said screw elements and utilize the same to produce relative movement in the direction of the thrust, in combination with a shiftable element operable by exteriorforcc in opposition to said thrust and shifting upon reversal of direction of the stress thereon, and means for utilizing sueh shifting movement to put the pilot mechanism into and out of relation for the above-described operation, together with a spring for the shiftable element normally tending to maintain said element and the pilot mechanism in the above-described thrust-relieving and thrust-utilizing relation.

. '31. Releasable thrust mechanism including continuously meshing screw members which, in the "direction of the thrust, are in thrust relation but with clearance afiordingbacklash upon the reversal of thrust andnormally locking by frictional engagement when the backlash is taken up in either direction, in

combination with pilot mechanism including a pilot screw having the same lead but of smaller pitch diameter so as to permit slip and rotation under thrust, and means for endwise shifting the pilot screw to cause and utilize.

I such rotation to rotate a locking screw element in a directionto relieve pressures on the locking threads and for then automatically screwing said locking thread member 'at the rate required to maintain such pressure relief, while the parts aremoving under load, a shiftable element operable by exterior force in opposition to the thrust on-the releasable;

mechanism and shifting upon-the reversal of the direction of the resultant stress thereon and means for utilizing such shifting to put the pilot mechanism into and out of operative position and a spring for the shiftable ele-- ment normally tending to maintain the same and the pilot mechanism in thrust receiving and thrust utilizing relation.

32. The combination specified by claim 23 wherein the locking sleeve has greater endwise play than the slip-sleeve.

33. The combination specified by claim 23, wherein the slip sleeve is endwise supported on ball bearings.

34. Asteplessratchet mechanism including a locking thread element, an endwise movable Worm engaging the same and normally looking therewith by friction underthrust, co'upied thereto, a pilot mechanism shiftable in a positive manner, to unlocksaid worm and then to utilize said thrust to rotate said Worm.

35. A stepless ratchet mechanism including a locking thread element, an endwise movable worm engaging the same and. normally looking therewith by friction under thrust, 'in combination with means for applying thrusts endwise of the worm and means for automatically rotating the worm to positively relieve its locking engagement with said locking thread element whensaid' worm'is to move endwise in the direction of thrust.

36. Thrust mechanism including a slipthread-screw and a rotary nut element adapt-. ed for relative slip and rotation under endthrust, the driving member of the thrusttransmitting elements being coupled in re ciprbcal rotary driving connection to the driven member of the pilotelements, the driven member of the thrust transmitting elements being coupled in reciprocal rotary driving connection to the driving member of the pilot mechanism, one of said couplings being positively variable for the purpose of alteringthe phase relationship'between the thrust transmitting elements and the ilot elements, and means for shifting said variable coupling,

whereby the-pilot elements are subjected to.

riven thrust and move said thrust'transmitting elements to a new condition of frictional lockand positively maintain said new condition. 38. In releasable thrust mechanism, lock screw elements and slip screw elements, the rotary members .of theflock'screw and slip screw being coupled in reciprocal rotary driving relation, the non-rotating members of the lock screw and-slip screw being coupled in 'fixed relation, in combination w th means for

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