Making The J-Bolt Alignment Fixture
Not being a professional contractor myself, I didn't know how much tolerance I had other than that which was stated in the drawings. Since this was considerably small, +-1/16", I saw no other way to make it dummy-proof than to make a rigid fixture. I started by making a jig on the floor of my shop on which I could simulate the mounting pad of the tower and use that to make a fixture. The fixture will then be used to locate the J-bolts with a high degree of accuracy. To a seasoned concrete guy this might be over-kill, but I couldn't think of any other way to do it whereby I didn't run an unacceptable risk for misalignment, the solution for which would probably be painful. If I had a crew and was going to complete this project in a matter of days, I might have opted for a less elaborate method but that wasn't the case.
This first pic shows four 4' x 8' sheets of cheap whatever it's called, like plywood but cheaper. Any good lumber yard should have this stuff. I used 1/2" material.
In the next pic you can see some scrap pieces of plywood used to tack the sheets together. You'll want to make sure you don't put these pieces in the way of your fixture.
This pic shows where you can start to get an idea of what I'm going to do. For a supply of real cheap steel tubing, I'm using the upper support rails for chain-link fence. You can get 10 foot'ers for only around 5 or 6 dollars. I wanted the fixture to be light yet fairly rigid and while this tubing may not be perfect, it's cheap and readily available almost anywhere.. One end is swedged for insertion into another tube, where I plan on welding them together for one contiguous tube. If you don't have a heli-arc (TIG Welder) you could probably clamp/screw the sections together with a reasonable amount of success too. The fixture doesn't necessarily support a load so the only force acting against the tubing is linear. I was unable to find lengths of this stuff longer than 10' but they may exist. My tower base section has a 14' 8-3/8" spread. This tubing will get welded to the alignment plates or templates to become the fixture. I had to push the racing boat (foreground) out of the way for this one. Good thing it's winter. The pieces of paper are being taped into location for the sake of plotting the triangle. It's just about impossible to see a good line on this type of wood.
This close-up shows the J-bolt template welded to the first tube. You can also see the small nail protruding from the 1/8" hole in the center of the template.
Below you can see a Vise-Grip in the foreground. This was used to help hold things in place prior to welding.
This is the center of the fixture, and will wind up in the very center of the foundation. To bypass the need for high tolerance in the location of the center hub, it was roughly located in the center but made out of 4" diameter pipe. That way, once the fixture is completed, the center of the equidistant triangle can be re-established by striking arcs onto a piece of steel plate which gets tack-welded onto the center pipe hub. At the intersection of the three arcs, a 1/8" hole will be drilled like the end plates have. All measurements are done with these holes.
Showing completed template detail.
The center. Note: the fixture is now up side down in this picture.