Boom lifts bring to mind bucket lifts that lift personnel high on power poles or construction sites. However, their are a wide array of smaller boom lifts for mechanical and even farm use. From a "cherry picker" that lifts a car engine to an all-purpose boom lift that is fitted to a tractor hitch, boom lifts can take the place of several strong people. Booms can be constructed with a welder, a plasma cutter and steel stock in conjunction with modular hydraulic components. You can alter the boom design -- particularly its base -- to fit a variety of applications.
Cut three lengths of 5-inch-square steel tubing using a plasma cutter. Make the cross-brace 3 feet wide, the vertical member 5 feet high and the boom arm 4 feet long.
Weld the vertical member using a MIG welder to the center of the cross-brace, forming a T-joint.
Cut two 10-inch-long, 5-inch-wide, .25-inch thick steel plates with a plasma cutter. Drill centered pilot holes, 2.5 inches from the ends of the plates. Drill them wider, using a 1.5-inch drill bit. Weld the plates at the opposite end of the T-joint so half of the plate laps to the vertical member and the other half -- the drilled half -- overhangs the end to act as a hinge for the boom.
Drill a pilot hole centered 2.5 inches from the end of the boom arm, and re-drill the hole 1.5 inches wide. Place the boom arm between the hinge flanges and slide a 7-inch bolt, 1.5 inches in diameter throughout the holes, forming the hinged joint. Use washers on each side and fasten it with two locking nuts.
Cut five 4-by-4 inch, .25-inch thick steel plates. Drill 1-inch holes in the center of four of them to correspond to the mounting holes of the hydraulic cylinder. Drill a larger 1.5- to 2-inch hole in the fifth plate to use a the chain hook on the end of the boom.
Weld the plate centered on the end of the boom, facing down.
Position the hydraulic cylinder with the base about halfway up the the inside of the vertical member and the tip of the chrome cylinder about 1 foot from the hinge on the boom arm. Adjust the position so the travel of the boom arm has the desired range of lift given the amount of travel of the hydraulic cylinder. Mark the appropriate locations of each end of hydraulic cylinder on the boom.
Weld the two sets of flanges in place -- two adjacent to the marks on the boom arm and two adjacent to the marks on the vertical member. Bolt the hydraulic cylinder in place.
Thread two hydraulic adapters into the hydraulic cylinder.
Thread two hydraulic hoses into the adapters.
Thread two hydraulic adapters to the other end of the hoses so they can be quickly coupled to whatever hydraulic source you want to use.
Fabricate the remainder of the stand. Either weld two feet onto the ends of the T at the boom lift's base, like a palette jack. Or weld flanges to the back of the back of the boom lift so it can be fastened to your tractor, fork lift or other implement.
Add additional bracing if you feel it's necessary for your application.
For some applications, consider welding a console on the side of the boom and mount lever-controls, spliced into the hydraulic controls. That will allow you to pressurize the lift from an external source, but operate it right at the lift.
Mechanical failure when lifting anything heavy can be dangerous. Your plans should be engineered and your welds executed by a certified welder.