What s a Screw Jack and How Do You Use It?

23 Sep

A screw jack, also called a jackscrew, is a type of jack frequently used to lift and support heavy loads. Small laboratory jacks are also usually types of screw jacks. It is also the name of a short story by Hunter S. Thompson, but that is not the subject of this article.

Screw jacks come in several forms, but they all feature the use of a screw to provide the lifting function of the jack. Frequently they are designed to combine the function of jack and jack-stand. Common varieties of screw jacks are rail-road jacks, foundation jacks, post jacks, scissors jacks for automobiles, leveling jacks for rvs and travel trailers and laboratory jacks. Simple screw jacks are easy to make for special and such home made screw jacks are often made by carpenters and handy-men for special purposes.

One common form of screw jack is the jack-post. Jack posts are frequently to correct sagging floors by raising and supporting floors where various types of problems have resulted in a depressed or sunken area in a floor. Of course, the floor must not be a slab floor. There must be floor beams which can be jacked and supported. It is necessary to first determine the reason for the problem and correct that problem. Failure to correct the problem will probably lead to recurrence of the problem or greater problems down the line.

If a jack post is being used to support the center of a floor beam that is simply too long, be certain that the jack-post has safe contact surfaces on both ends. If the bottom is on dirt or clay it must have either a large metal plate or be on a concrete pad made for that purpose. If it is on concrete, be certain that the end of the post is large enough to not break the concrete. The top of the post should be on a metal surface that will not move and is large and strong enough to not damage the beam or joist. Sometimes a large washer will fit over the pointed end often found on some jack posts. Many modern jack-posts have the correct type of ends so that such precautions are taken care of. If you chose to build your own screw jack be sure that you plan for proper ends for your jack.

Scissors type screw jacks are frequently provided for car jacks. They are smaller than traditional bumper type car jacks and are safer since they must be unscrewed to lower the vehicle. A scissors jack uses a screw jack to pull two pairs of arms together, forcing center pivot points apart to provide the jacking function. Laboratory jacks are usually made of several scissors jacks working together to lift and hold small platforms.

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