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552:
115:
22:
488:
170:
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205:
with a load table mounted on its top, which screws into a threaded hole in a stationary support frame with a wide base resting on the ground. A rotating collar on the head of the screw has holes into which the handle, a metal bar, fits. When the handle is turned clockwise, the screw moves further out
478:
seals reduced the price of low-cost hydraulic jacks and they became widespread for use with domestic cars. Screw jacks still remain for minimal-cost applications, such as the little-used tyre-changing jacks supplied with cars, or where their self-locking property is important, such as for horizontal
443:
Screw jacks are limited in their lifting capacity. Increasing load increases friction within the screw threads. A fine pitch thread, which would increase the advantage of the screw, also reduces the speed of which the jack can operate. Using a longer operating lever soon reaches the point where the
661:
The idea of incorporating jack screws into electrical connectors was not considered novel in the late 1950s and early 1960s. Some patents from that era show pairs of jackscrews on opposite sides of a multi-pin connector. Another shows a single central jackscrew. These patents mention the phrase
600:
freighter, broke loose immediately after takeoff and smashed through the rear bulkhead. The cockpit voice and flight data recorders were knocked off line, hydraulic lines were severed and most critically, the horizontal stabilizer actuator’s jackscrew was destroyed, rendering the aircraft
434:
whose output force turns the screw. So the mechanical advantage is increased by a longer handle as well as a finer screw thread. However, most screw jacks have large amounts of friction which increase the input force necessary, so the actual mechanical advantage is often only 30% to 50% of this
653:
connectors, where they serve primarily to prevent accidental disconnection. On larger connectors such as the one illustrated, the jack screws also help align the connectors and overcome the large frictional forces involved in inserting or removing the connector. When unscrewed, they allow the
499:
The large area of sliding contact between the screw threads means jackscrews have high friction and low efficiency as power transmission linkages, around 30%–50%. So they are not often used for continuous transmission of high power, but more often in intermittent positioning applications.
162:
470:, after two failed attempts by other means. The maximum mechanical advantage possible for a hydraulic jack is not limited by the limitations on screw jacks and can be far greater. After World War II, improvements to the grinding of
538:
that uses a recirculating-ball nut to minimize friction and prolong the life of the screw threads. The thread profile of such screws is approximately semicircular (commonly a "gothic arch" profile) to properly mate with the
222:, which means when the rotational force on the screw is removed, it will remain motionless where it was left and will not rotate backwards, regardless of how much load it is supporting. This makes them inherently safer than
306:
527:
is used, although it has higher friction, because it is easy to manufacture, wear can be compensated for, it is stronger than a comparably sized square thread and it makes for smoother engagement.
613:
operations. Aside from their size, these frequently look no different from the screw jacks used to lift buildings off their foundations. Machinist's jacks can be as simple as a
340:
370:
416:
393:
555:
A Boeing 737 uses an adjustable horizontal stabilizer, moved by a jackscrew, to provide the required pitch trim forces. Generic stabilizer illustrated.
609:
A machinist's jack is a miniature screw jack used to support protruding parts of a workpiece or to balance clamping forces on that workpiece during
248:
669:
of the screws as well as various alignment pins may be mixed in order to prevent the wrong connector from being connected to the wrong socket.
654:
connector halves to be taken apart. Jackscrews in electrical connectors may have ordinary screw heads or extended heads designed as
543:. The disadvantage to this type of screw is that it is not self-locking. Ball screws are prevalent in powered leadscrew actuators.
206:
of the base, lifting the load resting on the load table. In order to support large load forces, the screw is usually formed with
32:
90:
666:
62:
835:
226:, for example, which will move backwards under load if the force on the hydraulic actuator is accidentally released.
850:
69:
47:
238:
of a screw jack, the ratio of the force the jack exerts on the load to the input force on the lever ignoring
593:
76:
582:
317:
235:
58:
817:
347:
142:. It is commonly used to lift moderate and heavy weights, such as vehicles; to raise and lower the
578:
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202:
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143:
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of aircraft; and as adjustable supports for heavy loads, such as the foundations of houses.
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646:
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571:
8:
400:
377:
739:
845:
504:
492:
419:
83:
751:
Angilo M. Di Monte, Electrical
Connector with Resiliantly Mounted Removable Contacts,
597:
524:
471:
464:
395:
is the length of the jack handle, from the screw axis to where the force is applied
43:
840:
618:
567:
508:
665:
Jack screws may have either male or female threads, and on some connectors, the
650:
448:
427:
223:
783:
768:
753:
301:{\displaystyle {\frac {F_{\text{load}}}{F_{\text{in}}}}={\frac {2\pi r}{l}}\,}
829:
456:
135:
559:
Jackscrews are also used extensively in aircraft systems to raise and lower
693:
540:
629:
218:
An advantage of jackscrews over some other types of jack is that they are
810:
207:
551:
683:
678:
531:
459:'s hydraulic press concept were applied to the successful launching of
114:
688:
610:
535:
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139:
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is also used for the captive screws that draw the two parts of some
21:
520:
239:
189:
662:"jack screw" incidentally, without asserting a claim to the idea.
649:
together and hold them mated. These are commonly encountered on
487:
475:
452:
185:
161:
431:
181:
178:
169:
725:
S. L. Walton, Drill Press Vise
Doubles as Machinist.s Jack,
149:
39:
589:
174:
712:
By Heinz K. Flack and Georg Möllerke, ed., Machine Jack,
495:
involved entire city blocks being lifted with jackscrews.
372:
is the rotational force exerted on the handle of the jack
111:
Mechanical lifting device operated by turning a leadscrew
514:
570:
airliner due to design flaws resulted in the crash of
511:
is used, because it has the lowest friction and wear.
633:
An electronics module mounted on the back of a large
403:
380:
350:
320:
251:
118:
A 2.5-ton screw jack. The jack is inserting the bar
503:In heavy-duty applications, such as screw jacks, a
766:Lincoln E. Roberts, Electrical Connecting Device,
410:
387:
364:
334:
300:
821:. New York: P. F. Collier & Son Company.
430:in series; the long operating handle serves as a
827:
451:. This was encouraged in 1858 when jacks by the
800:, last modified July 2017, retrieved June 2021.
637:incorporating two very long T-handle jackscrews
201:A screw jack consists of a heavy-duty vertical
447:Screw jacks have now largely been replaced by
48:introducing citations to additional sources
624:
781:Ronald G. Hartwell, Electrical Connector,
592:armoured vehicle being transported aboard
581:due to deficient maintenance brought down
444:lever will simply bend at its inner end.
407:
384:
361:
342:is the force the jack exerts on the load.
331:
297:
808:
628:
550:
486:
168:
160:
148:
113:
38:Relevant discussion may be found on the
229:
173:Antique wooden jackscrew for repair of
828:
157:operates this automotive scissor jack.
515:Industrial and technical applications
604:
122:in the holes at the top and turning.
15:
519:In technical applications, such as
13:
809:Reynolds, Francis J., ed. (1921).
714:Illustrated Engineering Dictionary
14:
862:
335:{\displaystyle F_{\text{load}}\,}
577:The failure of a jackscrew on a
566:The failure of a jackscrew on a
31:relies largely or entirely on a
20:
798:Repairing Electrical Connectors
621:in it to serve as a jackscrew.
482:
426:The screw jack consists of two
365:{\displaystyle F_{\text{in}}\,}
790:
775:
760:
745:
732:
729:, No. 1 (Jan. 1966); page 127.
719:
706:
438:
196:
138:that is operated by turning a
1:
699:
213:
165:Antique locomotive screw jack
594:National Airlines Flight 102
7:
716:, Springer, 1997; Page 349.
672:
546:
534:is a more advanced type of
10:
867:
818:Collier's New Encyclopedia
583:Alaska Airlines Flight 261
236:ideal mechanical advantage
742:, retrieved July 1, 2021.
727:Popular Science, Vol. 188
491:In the 19th century, the
479:stabilizers on aircraft.
836:Mechanisms (engineering)
787:, granted Mar. 16, 1965.
625:In electronic connectors
184:(Ethnographic Museum of
772:, granted Apr 13, 1965.
757:, granted Apr. 3, 1962.
579:McDonnell Douglas MD-80
851:Construction equipment
638:
561:horizontal stabilizers
556:
496:
412:
389:
366:
336:
302:
193:
166:
158:
144:horizontal stabilizers
123:
784:U.S. patent 3,173,734
769:U.S. patent 3,178,669
754:U.S. patent 3,028,574
647:electrical connectors
632:
554:
490:
413:
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367:
337:
303:
172:
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152:
117:
635:electrical connector
572:Aeroflot Flight 8641
401:
378:
348:
318:
249:
230:Mechanical advantage
120:(visible lower left)
44:improve this article
411:{\displaystyle l\,}
388:{\displaystyle r\,}
796:Douglas W. Jones,
639:
557:
497:
493:Raising of Chicago
408:
385:
362:
332:
298:
194:
167:
159:
124:
812:"Jackscrew"
738:Mike's Workshop,
605:Machinist's jacks
598:Boeing 747-400BCF
358:
328:
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109:
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601:uncontrollable.
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740:Machinist Jacks
737:
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711:
707:
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675:
627:
615:threaded spacer
607:
568:Yakovlev Yak-42
549:
517:
509:buttress thread
485:
474:and the use of
449:hydraulic jacks
441:
428:simple machines
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224:hydraulic jacks
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134:, is a type of
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651:D-subminiature
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472:hydraulic rams
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42:. Please help
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541:bearing balls
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505:square thread
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477:
473:
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467:Great Eastern
462:
458:
454:
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422:of the screw.
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61: –
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55:Find sources:
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35:
34:
33:single source
29:This article
27:
23:
18:
17:
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694:Roller screw
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483:Applications
466:
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310:
233:
220:self-locking
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217:
208:Acme threads
200:
131:
127:
125:
119:
97:
87:
80:
73:
66:
54:
30:
656:thumbscrews
596:in 2013, a
525:Acme thread
455:company to
439:Limitations
197:Description
59:"Jackscrew"
830:Categories
700:References
684:Ball screw
679:Acrow prop
585:in 2000.
574:in 1982.
532:ball screw
214:Advantages
132:screw jack
70:newspapers
846:Actuators
689:Leadscrew
643:jackscrew
641:The term
611:machining
536:leadscrew
521:actuators
286:π
155:leadscrew
140:leadscrew
128:jackscrew
100:July 2017
40:talk page
673:See also
547:Aviation
465:SS
435:figure.
240:friction
190:Bulgaria
667:genders
617:with a
418:is the
84:scholar
841:Screws
476:O ring
461:Brunel
457:Bramah
453:Tangye
311:where
186:Elhovo
182:wheels
86:
79:
72:
65:
57:
523:, an
432:lever
203:screw
179:wagon
130:, or
91:JSTOR
77:books
619:bolt
590:MRAP
530:The
420:lead
327:load
260:load
242:is
234:The
177:and
175:cart
136:jack
63:news
563:.
507:or
463:'s
46:by
832::
815:.
658:.
588:A
357:in
270:in
210:.
188:,
153:A
126:A
405:l
382:r
353:F
323:F
293:l
289:r
283:2
277:=
266:F
256:F
192:)
102:)
98:(
88:·
81:·
74:·
67:·
50:.
36:.
Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.
