A screw jack is a type of jack which is operated by turning a leadscrew. It is also known as a jackscrew, and are commonly used as car-jacks. It looks like a prop and always has the same function with scaffold.

 

A screw jack is a type of jack which is operated by turning a leadscrew. It is also known as a jackscrew, and are commonly used as car-jacks. It looks like a prop and always has the same function with scaffold.

A screw jack'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 screw jacks 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.

screw jacks form vital components in equipment. For instance, the failure of a screw jack 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 screw jack 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 screw jack secured the damage until landfall.

A screw jack'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 screw jacks 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.

screw jacks form vital components in equipment. For instance, the failure of a screw jack 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 screw jack 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 screw jack secured the damage until landfall.