A jackscrew's compressive force is obtained through the tension force applied by its leadscrew. An Acme thread is most often used, as this thread is very strong and can resist the large loads imposed on most jackscrews while not being dramatically weakened by wear over many rotations. These types are self-locking, which makes them more intrinsically safe than other jack technologies like hydraulic actuators which require continual pressure to remain in a locked position. Most jackscrews are lubricated with grease.
Advanced screw mechanisms may use a recirculating-ball nut to minimize friction and prolong the life of the screw threads, but such jackscrews are usually not self-locking. The thread profile of such screws is semicircular, not trapezoidal as in an Acme thread.
Jackscrews form vital components in equipment. For instance, the failure of a jackscrew on a McDonnell Douglas MD80 due to a lack of grease resulted in the crash of Alaska Airlines Flight 261 off the coast of California in 2000.
The jackscrew figured prominently in the classic novel Robinson Crusoe. It was also featured in a recent History Channel program as the saving tool of the Pilgrims' voyage — the main crossbeam, a key structural component of their small ship, cracked during a severe storm. A farmer's jackscrew secured the damage until landfall.
FAA FINDS `NO SAFETY ISSUES' WITH AIRLINE'S JACKSCREWS PROBLEM WITH TAIL COMPONENT LED TO CRASH OF ALASKA PLANE IN 2000.(Business)
Jan 14, 2006; Byline: JAMES WALLACE P-I aerospace reporter Alaska Airlines inspectors in Seattle found 15 incidents of "dry" jackscrews...