[TheForge] bridge crane

[John Husvar]

On Sep 27, 2005, at 6:31 AM, Justin Fellenz wrote:

> YOu know, I may have used the wrong term. The crane I was referring to
> is anchored in pins at the floor and the ceiling of the shop with a
> vertical, pivoting I-beam between them and the crane part cantilevered
> out from the vertical post 4' down from the top or so.

That's called a jib crane. They can be placed on a column, built as  
you describe or be self-supporting on a large floor plate over a  
footing made for the purpose.

Gantry cranes run on one floor rail and one column-mounted runway  
rail (single-leg gantry) or on floor tracks, (double-leg gantry) or  
even on tires with capability to move their loads in three  
dimensions. (free-moving gantry) Check out the cranes used on port  
docks for unloading ships and placing containers on trucks. The  
unloading cranes are cantilevered gantry cranes on rails and the  
mobile ones that move containers around or load them on trucks are  
free-moving gantries on tires. Some lumberyards also use that kind of  
crane.

Whatever you (generic) decide you need or want in a crane, start by  
specifying the building structure to support it or having an engineer  
check your existing building or plans for adequacy. I repaired or  
recommended condemnation of too many failured overhead cranes not to  
recommend that! It doesn't happen often with light duty shop cranes,  
but once is usually more than enough, at least for that particular  
building -- or operator. :)

Even just a 1-ton top-running crane can place surprising amounts of  
stress on a building's columns, footings, etc. An underhung crane  
(joist-mounted) puts a lot of stress on the joists and the columns,  
which must be built for the purpose. You might also find your crane  
weighs more than its rated load.

John, whose longest employment was more than 20 years in building,  
modifying, and repairing overhead cranes and automated material  
handling systems of all types. :)