It’s another weekend so that must mean another weekend warrior project. This time, it’s the fixed base for a mast such a flagpole or bird house. The theory of this base is that the mast has two holes drilled through it and bolts sandwich the mast between the two uprights of the base. Anytime you need to service the mast, you remove the bottom bolt and pivot the mast on the upper bolt.
I take no credit for the idea. When I was a kid, my grandfather built this setup for a Martin House.
The materials are pretty easy. The only thing you may need to hunt and scrounge for will be a couple pieces of “U” channel steel. The stainless steel bolts and the concrete are available at most hardware and he improvement stores.
The prep work for the base was done back in the shop. I clamped the two sides together and drilled a small pilot hole through. The further apart the holes, the easier the pivot. In my case, the best I could do was 18″ center to center – I needed 4″ of clearance at the bottom and 36″ of the base would be below ground level so given my salvaged steel, I had 22″ to work with and the holes can’t be at the very ends. Next, I sandwiched the mast between the base sides, made sure the sides were even, and the base and mast were parallel. Then I drilled the pilot holes into the mast. I separated everything and drilled the holes to their final size.
My base sides are steel and my salvaged mast is aluminum. An alchemist will tell you this combination has a tendency to react in the presence of moisture and corrosive elements like salt (and fertilizer). To minimize the problem, I am using stainless steel hardware and fabricated some polystyrene washers (but you can buy them easy enough). The sequence will be stainless washer, steel base side, poly washer, aluminum mast, poly washer, steel base side, stainless washer, and finally a lock nut.
With the base and mast drilled, I cut some scrap wood to mimic the size of the mast, and temporarily assembled the base with the wood. The base need to be anchored in the concrete with the proper spacing to accept the mast but you definitely don’t want to try and work do the concrete work with the mast in place !
I planned to use a sonatube form in the hole but the local hardware store only had 12″ tubes and the steel “U” channel I found would not fit so I just cleaned up the sides of the hole I dug and poured the concrete directly in the hole.
It’s important to know how deep is the possible frost line in your area. Back in Maine, the rule of thumb was 48″. Here on the Eastern Shore it’s only 22″. I dug down to 36″ just to be safe. The depth and diameter of the hole dictates how much concrete you need. If you use a sonatube, it has the calculation right on the side. A 12″ sonatube needs 1.3 80 lb bags per foot so I would have needed 4 bags. My hole was bigger that 12″ round and I needed 6 bags. It turned out that wasn’t even enough so I scrounged some broken pieces of paver stones left over from the walkway/patio project and just kept tossing a few in at a time as I added the concrete.
The final tally was 480 lbs of concrete and another 120 lbs of random chunks of pavers. The base is just under 5 feet with 36″ in concrete and 22″ above ground.
In a few days I’ll remove the spacers. In a few weeks I hope to raise the mast