Posted by Steve Kanavas on Thursday, January 18, 2001 at 9:52AM :
In Reply to: Gin Pole posted by Ed C. on Wednesday, January 17, 2001 at 2:21PM :
Glad to see people concerned with safety of these things. I made mine in a 2 hour emergency to throw shingles on my roof. The shingle guy just offloaded the truckload in the driveway And I wasn't about to carry 28 square up a damn ladder.
Loading on the poles is essentially compressive. The tensile load is taken by the support cable that would anchor to the back of the truck. This better be strong with a good anchor!
Knowing this, any heavy wall metal tube over 2" diameter can take a hell of a lot of compressive and hoop stress loading. Fortunately for a gin pole or A frame design, the vertically lifted load is compressive on the pipes, with minimal side load energy input as the load is hanging on a rope like a pendulum.
Any weak sectional joints or kinks in the pipe will be disasterous. They will propagate a bend and fail easily. The problem with multiple section pipe is that the stresses are concentrated at the joints.
The top of the A frame must be connected tightly together to cancel torque inputs that would otherwise twist the A frame. Screw together sectional joints will simply turn when torqued. The wonders of a thread!
My mickey mouse 4X4 thing works ok, but one must realize it's just wood and therefore load it lightly. I don't think I would lift anything over 500 pounds unless all the termites joined hands.
sak
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