The screw jack, one of the simplest and most basic machines ever invented, is a willing workhorse that has helped people time and again, around the homestead, in construction work, and in the field of maintenance. The weight-bracing device may cost anywhere from $10 to $24 (depending on its size) if purchased from a department store or mail-order house. But if you're adept at scavenging and have access to welding equipment and a heavy-duty drill (or oxyacetylene torch), here's how to make a screw jack on your own, using materials that are often found lying around in junk piles, free for the taking.
The screw jack has only one moving part, which does all the work: a nut that travels up the threads of its bolt. The homemade screw jack is turned with a wrench and consists of six parts: a bolt, a matching nut, a section of pipe, a cap plate, a baseplate, and a top plate (which can be replaced by a nut, if desired).
For most of my jacks, I use Schedule 40 2" pipe and 1/4"- to 1/2"-thick steel plate cut into 3" or 4" squares. When it comes to the nut and bolt, the idea is "the bigger, the sturdier," especially on heavy jobs such as house leveling. For my last model, I used a 6"-long, 1"-diameter bolt with 10 threads per inch. [EDITOR'S NOTE: In high-load situations, an acme-threaded bolt—generally used for power transmissions—would be the preferred choice…but you'd need to find a matching nut.] I found the pipe and steel plate in a scrap pile behind a local machine shop. You should be able to scrounge such material from similar places or else purchase it inexpensively at a junkyard.
To begin, you'll need to cut your pipe to tie appropriate length for the job at hand. Next, weld the baseplate onto the bottom of this conduit (see the diagram). Now, cut (with an oxyacetylene torch) or drill a hole that's slightly larger than the diameter of the bolt's shaft into the cap plate. (If the pipe you're using is galvanized, be sure to do the welding in a well-ventilated area.) Slip the bolt headfirst into the open end of the pipe (so that the head can act as a brake if you try to turn your jack too far), slide the cap plate down over the threaded shaft, and weld it to the pipe. All you need to do now is to twist on the moving nut and add a bearing surface to the top end of the bolt. Sometimes I attach a top plate, and at other times I merely tack on an extra nut, flush with the top of the bolt. Once that's done, your screw jack’s ready to use!
If you want to produce a more versatile jack—without expending much effort—just use two lengths of pipe. A section 2 1/2" to 3" in diameter works best for the outer portion of a machine of this size, and you'll need a second length about 1" longer and one size smaller than the first, to fit inside.
Begin by welding the bottom plate onto the first pipe, as before. Next, at 6-inch intervals, pass the drill through the second pipe to form 1/2" holes, and slide a sturdy bolt, about 6" long, through a pair of the openings to act, as a holding pin. [EDITOR'S NOTE: Even better, drill additional holes in the bottom section, and run the pin through both pipes for double stability.] Now, weld the cap plate onto the inner conduit, insert the nut and bolt, and there you have it: at an expenditure of a half-hour's labor, a telescoping screw jack similar to the ones sold in major hardware outlets.
By the way, these marvelous machines work in any direction, so they're by no means limited to vertical jobs. With a little imagination, you can use them as clothes poles, plant hangers, coat racks, and even chinning bars!
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