Here are some photos documenting the fabrication of the spreader bar.
Since this needed to be fabricated as accurately as possible I first used a CNC router to cut out an Aluminum template that we could then use to guide the tip of the plasma cutter.
The template has a 3/16″ offset on the the edges that are going to be cut to account for the distance between the side of the plasma cutters torch tip and the cut point. I then drilled hole in the steel plate near the edge of all the areas to be but because the arc for the plasma cutter is best started on a edge of a plate. The large space in the middle of the template is not going to be cut out. It represents where the bars will be placed. The edge does not have an offset and using a sharp scribe I can place a thin line in the steel so that when we can line the ends of the bars up it.
Here you can see several of the plates cut out and in various stages of being finished. Notice the diamond shape scribed in the center.
Here is one of the 15′, 3″x3″ square tubes with the 30 degree angle cut down the vertex.
This is a close up of the end of the bar. Cutting this angle was a bit of a chore. I had to measure from the end of the bar, along the edge, to the proper distance that described the face. Then I wrapped a bit of copper flashing around the bar, intersecting these points, and then traced the line it created. I then cut the tube with a plasma cutter and ground down precisely to the mark
Once all the plates and bars were prepared it all got layed out, leveled and plumbed. Here I got to work in an actual patch of sunlight — unheard of most day in a workshop.
This big yellow thing is one of the shackles that gets connects the spreader bar to the straps that go up to the crane hook or down to the hose. Here we are testing to be sure that the shackles fit and can reach the angles they need to.
The finished spreader bar tacked together, waiting to be welded.
Finnaly, me, relaxing in my gigantic traingle with a root beer (seriously). Photo by Benna.
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