Automatic Screw Jack

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Screw type mechanical jacks were very common for jeeps and trucks of World War II vintage. For example, the World War II jeeps were issued the "Jack, Automobile, Screw type, Capacity 1 and 1/2 ton", Ordnance part number 41-J-66. This jacks, and similar jacks for trucks, were activated by using the lug wrench as a handle for the jack's ratchet action to of the jack. The 41-J-66 jack was carried in the jeep's tool compartment. Screw type jack's continued in use for small capacity requirements due to low cost of production raise or lower it. A control tab is marked up/down and its position determines the direction of movement and almost no maintenance. The virtues of using a screw as a machine, essentially an inclined plane wound round a cylinder, was first demonstrated by Archimedes in 200BC with his device used for pumping water.

There is evidence of the use of screws in the Ancient Roman world but it was the great Leonardo da Vinci, in the late 1400s, who first demonstrated the use of a screw jack for lifting loads. Leonardo design used a threaded worm gear, supported on bearings, that rotated by the turning of a worm shaft to drive a lifting screw to move the load - instantly recognizable as the principle we use today.  We cant be sure of the intended application of his invention, but it seems to have been relegated to the history books, along with the helicopter and tank, for almost four centuries. It is not until the late1800s that we have evidence of the product being developed further. 

A jackscrew is a typeof jack which is operated by turning a lead screw. It is also known as a screw jack, and is commonly used as car-jacks. In the case of a screw jack, a small force applied in the horizontal plane is used to raise or lower large load.[Khurmi and Gupta, 2010]. Of the screw-type mechanisms, there are scissor jacks,common in newer cars, and bumper jacks, common in older cars. A jackscrew's compressive force is obtained through the tension force applied by its lead screw. 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.

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