It was time to pour the footing for the base of the mast and embed the Chromoly tube in the bottomless hole.
- 1x tube of painted, galvanized Chromoly (5′ 4″ x 2″ OD x 1/4″ wall)
- 5x 80 lbs of fiber concrete mix
- 1x 60 lbs of gravel
- 4x 1′ sections of not so carefully sliced leftover ground rod
- old shovel
- bubble level
- scrap 2×4 a couple of feet long
- 2x random green bungees
- aqua from hose as needed
My bottomless hole was at least as big as the one in DX Engineering’s guide for the OMNI-TILT antenna base. I had measured the depth to make sure the tube on top of the gravel would protrude ~20″ above ground.
What I didn’t know was just how much concrete I would need. Of course, to calculate the amount would be roughly the following formula:
But it wasn’t like I was digging a precision hole with that posthole digger! Where I found rocks and roots determined the shape more than anything. And I intentionally turned the bottom into a bit of a ball shape to add weight. At the same time, I was pulling out some good size rocks.
Gravel went in first, and it was just enough to achieve the goal of a couple of inches for drainage.
And now about those bungees. I disliked using string and trying to keep it taut and the inevitable fiddliness trying to adjust (and re-adjust) that for plumb. So, instead, I took four sections I had cut off from the old, mangled ground rod and drove them into the ground. And then set up two bungee cords intersecting roughly in the center of the hole. There’s zero precision in this setup itself and intentionally so. The accuracy for plumb comes out of the adjustment.
I inserted the painted tube into the hole and aligned the bottom end to where I wanted it to go and roughly checked with a bubble level for plumb. The point here is to get it aligned with the center of the hole approximately. Next, the bungee cords were wrapped around twice, once for each “axis.” Adjusting the line around the tube makes it move in either direction of the respective “axis.” Just tug on which side you want more slack. Feed some cord around the pipe to make larger movements.
Looking back, I’m laughing because I was very concerned this wasn’t going to work. However, this method worked out beautifully. It provided the setup with enough tension to keep the tube in place, yet allow for easy adjustments to keep it plumb. Small or large adjustments with a fair bit of precision are possible. And the ribs on the bungee cord provided a lot of friction to hold the tube in place under tension. The bungees gave when the concrete slid against it and returned to its original position afterward.
Sacrificing these cords for the cause was accepted. But, when done, it all cleaned up nicely with water.
At first, I thought five bags was overkill. Then two concrete bags in, I was worried and trying to work out how I’d get more bags here within the 45 minutes working time. Five loads in, and I was flush with the surface! I am breathing again. I would love to say I planned it that way. Oh, and the 2×4 is for poking the concrete while it’s setting up in the hole.
Now there are 400 lbs of fiber reinforced concrete holding the base 3’+ in the ground. I think this should be enough. The tube received a 2″ vinyl cap to keep stuff out. It should be draining through the gravel at the bottom.
Next is prepping the hinge for the aluminum pole.