Dome Crane

I quickly realized that factors in the dome design where going to make it difficult to assemble.
Building from the “bottom up” creates a situation where all the errors in the dome need to be corrected with a single bolt at the apex instead of being spread out around the base. Given that the dome weighs over a thousand pounds, has approximately 270 struts, the longest strut length is over six feet and the whole thing is 15 feet tall. I decided that “bottom up” wouldn’t work and that “top down” was the only way to go.
I thought of “jacks” at the edges to pick the dome up but they would need constant repositioning and wouldn’t be very stable.
A duel boom design became the obvious choice. The duel mast allowed pick points at two intersections of twelve struts. This would spread the lifting force evenly over the dome.
I was lucky enough to pick up a ton (maybe two tons) of angle iron that was destined for the trash. This was the perfect material to build the crane out of.
Working off sketches made in the lunch room on napkins I started cutting and drilling the members of the crane.
Some of the angle iron I got was galvanized and some of it had a zinc cadmium plating. The fumes from these materials are toxic which is why I wore a respirator capable of removing the toxic vapors form my air supply.
The crane is bolted together with 20mm cap screws. In addition to the braces that keep the towers vertical there are two 1/2” thick plates that connect the base of the crane to the masts.
Two snatch blocks are placed at the top of the masts, a 3/16” steel cable is routed through them and then hooked up to two come alongs each capable of a one ton lift.

Every member is labeled before disassembly. I learned that you can not put too many labels on this type of thing.
After the dome was completely assembled the crane was going to be removed. The crane was disconnected from the dome but there was little interest in removing it from the dome. In the end we left it set up. Having the crane in the dome for a week has inspired a loft and a observation deck for next year.
This is the tallest structure to come out of my work shop at 19’6”, which is why I felt it needed its own page.

Completed July 22nd, 2004

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