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33:
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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
489:
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
454:
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
672:
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
611:
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
445:
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
664:
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
510:
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.
173:
481:, 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
549:
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
233:, 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
317:
538:
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.
624:
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
351:
381:
427:
404:
566:
A Boeing 737 uses an adjustable horizontal stabilizer, moved by a jackscrew, to provide the required pitch trim forces. Generic stabilizer illustrated.
43:
620:
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
259:
680:
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.
677:
846:
665:
connector halves to be taken apart. Jackscrews in electrical connectors may have ordinary screw heads or extended heads designed as
554:. The disadvantage to this type of screw is that it is not self-locking. Ball screws are prevalent in powered leadscrew actuators.
217:
of the base, lifting the load resting on the load table. In order to support large load forces, the screw is usually formed with
861:
58:
604:
101:
73:
237:, for example, which will move backwards under load if the force on the hydraulic actuator is accidentally released.
593:
246:
828:
80:
249:
of a screw jack, the ratio of the force the jack exerts on the load to the input force on the lever ignoring
589:
471:
87:
213:
666:
625:
571:
154:
328:
69:
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645:
582:
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153:. It is commonly used to lift moderate and heavy weights, such as vehicles; to raise and lower the
856:
515:
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724:
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of aircraft; and as adjustable supports for heavy loads, such as the foundations of houses.
822:
851:
629:
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519:
411:
388:
750:
640:
661:
459:
438:
234:
94:
762:
Angilo M. Di Monte, Electrical
Connector with Resiliantly Mounted Removable Contacts,
562:
840:
467:
146:
704:
551:
406:
is the length of the jack handle, from the screw axis to where the force is applied
125:
676:
Jack screws may have either male or female threads, and on some connectors, the
218:
32:
794:
779:
764:
694:
689:
542:
312:{\displaystyle {\frac {F_{\text{load}}}{F_{\text{in}}}}={\frac {2\pi r}{l}}\,}
699:
621:
570:
Jackscrews are also used extensively in aircraft systems to raise and lower
546:
165:
150:
498:
229:
An advantage of jackscrews over some other types of jack is that they are
172:
17:
821:
531:
250:
200:
470:'s hydraulic press concept were applied to the successful launching of
180:
160:
486:
463:
196:
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is also used for the captive screws that draw the two parts of some
673:"jack screw" incidentally, without asserting a claim to the idea.
639:
561:
497:
442:
192:
189:
179:
171:
159:
124:
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together and hold them mated. These are commonly encountered on
600:
185:
26:
736:
S. L. Walton, Drill Press Vise
Doubles as Machinist.s Jack,
50:
723:
By Heinz K. Flack and Georg Möllerke, ed., Machine Jack,
506:
involved entire city blocks being lifted with jackscrews.
383:
is the rotational force exerted on the handle of the jack
122:
Mechanical lifting device operated by turning a leadscrew
54:
581:
airliner due to design flaws resulted in the crash of
522:
is used, because it has the lowest friction and wear.
644:
An electronics module mounted on the back of a large
414:
391:
361:
331:
262:
129:
A 2.5-ton screw jack. The jack is inserting the bar
514:In heavy-duty applications, such as screw jacks, a
777:Lincoln E. Roberts, Electrical Connecting Device,
421:
398:
375:
345:
311:
832:. New York: P. F. Collier & Son Company.
441:in series; the long operating handle serves as a
462:. This was encouraged in 1858 when jacks by the
811:, last modified July 2017, retrieved June 2021.
648:incorporating two very long T-handle jackscrews
212:A screw jack consists of a heavy-duty vertical
458:Screw jacks have now largely been replaced by
8:
59:introducing citations to additional sources
792:Ronald G. Hartwell, Electrical Connector,
603:armoured vehicle being transported aboard
592:due to deficient maintenance brought down
455:lever will simply bend at its inner end.
418:
413:
395:
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372:
366:
360:
353:is the force the jack exerts on the load.
342:
336:
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308:
290:
279:
269:
263:
261:
49:Relevant discussion may be found on the
716:
184:Antique wooden jackscrew for repair of
168:operates this automotive scissor jack.
526:Industrial and technical applications
7:
133:in the holes at the top and turning.
530:In technical applications, such as
820:Reynolds, Francis J., ed. (1921).
725:Illustrated Engineering Dictionary
25:
346:{\displaystyle F_{\text{load}}\,}
588:The failure of a jackscrew on a
577:The failure of a jackscrew on a
42:relies largely or entirely on a
31:
809:Repairing Electrical Connectors
632:in it to serve as a jackscrew.
437:The screw jack consists of two
376:{\displaystyle F_{\text{in}}\,}
740:, No. 1 (Jan. 1966); page 127.
149:that is operated by turning a
1:
176:Antique locomotive screw jack
605:National Airlines Flight 102
727:, Springer, 1997; Page 349.
545:is a more advanced type of
878:
829:Collier's New Encyclopedia
594:Alaska Airlines Flight 261
247:ideal mechanical advantage
753:, retrieved July 1, 2021.
738:Popular Science, Vol. 188
502:In the 19th century, the
490:stabilizers on aircraft.
847:Mechanisms (engineering)
798:, granted Mar. 16, 1965.
636:In electronic connectors
195:(Ethnographic Museum of
783:, granted Apr 13, 1965.
768:, granted Apr. 3, 1962.
590:McDonnell Douglas MD-80
862:Construction equipment
649:
572:horizontal stabilizers
567:
507:
423:
400:
377:
347:
313:
204:
177:
169:
155:horizontal stabilizers
134:
795:U.S. patent 3,173,734
780:U.S. patent 3,178,669
765:U.S. patent 3,028,574
658:electrical connectors
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314:
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646:electrical connector
583:Aeroflot Flight 8641
412:
389:
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329:
260:
241:Mechanical advantage
131:(visible lower left)
55:improve this article
422:{\displaystyle l\,}
399:{\displaystyle r\,}
807:Douglas W. Jones,
650:
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504:Raising of Chicago
419:
396:
373:
343:
309:
205:
178:
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135:
823:"Jackscrew"
749:Mike's Workshop,
616:Machinist's jacks
609:Boeing 747-400BCF
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16:(Redirected from
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612:uncontrollable.
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751:Machinist Jacks
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638:
626:threaded spacer
618:
579:Yakovlev Yak-42
560:
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520:buttress thread
496:
485:and the use of
460:hydraulic jacks
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439:simple machines
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235:hydraulic jacks
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145:, is a type of
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662:D-subminiature
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483:hydraulic rams
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53:. Please help
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516:square thread
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478:Great Eastern
473:
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433:of the screw.
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72: –
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67:
66:Find sources:
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45:
44:single source
40:This article
38:
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29:
28:
19:
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803:
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705:Roller screw
675:
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494:Applications
477:
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436:
321:
244:
231:self-locking
230:
228:
219:Acme threads
211:
142:
138:
136:
130:
108:
98:
91:
84:
77:
65:
41:
667:thumbscrews
607:in 2013, a
536:Acme thread
466:company to
450:Limitations
208:Description
70:"Jackscrew"
841:Categories
711:References
695:Ball screw
690:Acrow prop
596:in 2000.
585:in 1982.
543:ball screw
225:Advantages
143:screw jack
81:newspapers
18:Screw jack
857:Actuators
700:Leadscrew
654:jackscrew
652:The term
622:machining
547:leadscrew
532:actuators
297:π
166:leadscrew
151:leadscrew
139:jackscrew
111:July 2017
51:talk page
684:See also
558:Aviation
476:SS
446:figure.
251:friction
201:Bulgaria
678:genders
628:with a
429:is the
95:scholar
852:Screws
487:O ring
472:Brunel
468:Bramah
464:Tangye
322:where
197:Elhovo
193:wheels
97:
90:
83:
76:
68:
534:, an
443:lever
214:screw
190:wagon
141:, or
102:JSTOR
88:books
630:bolt
601:MRAP
541:The
431:lead
338:load
271:load
253:is
245:The
188:and
186:cart
147:jack
74:news
574:.
518:or
474:'s
57:by
843::
826:.
669:.
599:A
368:in
281:in
221:.
199:,
164:A
137:A
416:l
393:r
364:F
334:F
304:l
300:r
294:2
288:=
277:F
267:F
203:)
113:)
109:(
99:·
92:·
85:·
78:·
61:.
47:.
20:)
Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.
