What wall thickness should be used for a steel tubing boom crane?

[mudrat]

TL;DR

Class 3 lever design, how to calculate buckling at force point.

Hello, I am a retired electrical engineer who likes to tinker and invent. As I am getting older I find the moving of logs is getting harder to do, so I am thinking of building a boom crane to attach to the 3 pt hitch on one of my tractors.

The design would basically be a class 3 lever, with a distance of 16" from fulcrum to force, and 48" from force to load. With a max load of 500#, the force is 2000#.

Using A39 steel tube, 2" square, I am wondering about what wall thickness to use. There will be a reinforcing plate at the force point and a tension strap/rod along the top, but I am looking to calculate based on the simplified design of point load and force without any reinforcement of the tube.

It has been way to may years since my basic strength of materials courses in university to remember the formulas. Searching the net has only brought up distributed load on beams. It did bring me to this site!

I would just like to get an idea of how to calculate the strength needed to prevent buckling at the force point.

Mudrat

 

[jrmichler]

We need a sketch to properly understand your question.

 

[Baluncore]

A jib crane mounts on the top link of a three point linkage and is raised by lifting the two lower arms. Here is a picture of that version.
http://hayesproducts.com.au/product-category/tractor-jib-crane/

There is another version that mounts on the lower linkage, it has lower lift because it employs a standard top link. Here are some free DIY plans.
https://www.kurraglenindustries.com.au/free-tractor-3pl-boom-plans.htm

 

[mudrat]

The Hayes 500 kg unit is along the lines of what I am thinking of. It is twice the capacity, unknown boom length.

They use the equivalent of 3" x 2" 3/16" wall tube. Also at 60 kg it is heavier than what I want.