Saturday, August 18, 2012

Two man operation

Bridge building is an unending learning operation and I love it! Here is how I rigged and set the two gin poles for bridge number six.

First set up a nice tripod rigged with  a come-a-long that can be used to lift the pole up about 30 degrees. This replaced the 8 to 10 men I saw used used in Chester, NH.

An A-frame, hinged at the bottom with bolts and blocks is clamped to the top chord of the bridge truss and tied back to an anchor with a rope fence stretcher. This replaced the front end loader I tried once at South Wayne and the 4 men on two rope fence stretchers used at south Wayne for the second try.

The winch at the bottom of the pole driven by a power drill will do the heavy lifting. You can see in this picture that the drill is mounted to some support planks. The cable from the winch is routed to a snatch block pulley at the top of the pole, then to a second snatch block pulley attached to the top of the A-frame and finally anchored to the top of the gin pole. This all came about because one of my helpers, Jerry asked, why I didn't use the nice powerful winch at the bottom of the gin pole to do the lifting?

Adding a remote switch to the power line allowed me to do two jobs, first control the drill and second hold the rope tied to the gin top to keep it from swinging left or right during lifting. And I thought that just maybe I could make this a one man operation. Not a good idea, too risky. Better safe than sorry.

As the pole is raised by the winch it will be come more unstable and the second man will need to help control the pole at the bottom. The winch is used until the two snatch blocks are about 5 to 6 feet apart and then turned off. The winch operator then goes to the rope fence stretcher on the A-frame and gently pulls the A-frame to finish the lift and the gin pole is in place against the top chord where it can be secured and re-rigged to now lift the bridge truss. Double duty for the nice powerful winch, pretty cool!

A new school year starts in a few days. As an educator the experience of learning how to do this by watching it done 4 times in Chester, NH and doing it 4 times in South Wayne, WI lead me to this more efficient and improved method.  Why?

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