The base plate is the foundation of the hexagonal beam serving as the mounting point for spreader arms, center post and attachment of the beam to the mast. As such, strength and stability are of the utmost importance.
This base plate is cut from a 12 inch square piece of T6-6061 aluminum plate 3/16 inch thick. This type aluminum is quite tough and unlikely to bend. Two U bolts are installed for each of the six spreader arms. Two square base floor flanges are mated on the top and bottom of the base plate; the top for mounting the center post and the bottom for attaching the beam to a mast. The inside diameter of each of the flanges is 1.31 inches, a standard size for one inch pipe. This is close enough for most push up masts also on the bottom and for one inch pvc used to build the center post. Unused holes shown in the photo at left are for mounting a larger flange on the bottom for use with a mast greater in size than the push up mast.
The U bolts and mounting hardware should be stainless steel for resistance to corrosion although less expensive zinc hardware can be used and will still last for years in most environments.
The plate can be cut with a hack saw, a chop saw or even a skill saw with the appropriate metal cutting blade. The holes can be drilled with a drill press if available and with a hand drill if necessary. Use the measurements on the sketches here for this. After drilling the holes for the U bolts you can place the flange in the middle and mark the holes for mounting the flanges. The flanges are on opposite sides of the plate so the same four holes can be used for both. Since the flanges are a good fit for only a 1.3 inch O.D. pipe, you can consider use of the bracket/U bolt arrangement we now use on the commercial version that will allow use of several standard mast sizes. See it here and you can buy the parts here.
2. Install U bolts and flanges
Use lock washers for all the hardware fittings as the wind is doing all it can to disassemble your hex beam.
Some feel that a reinforcing collar should be slipped over the spreader arms where the U bolts clamp them to avoid damage to the tubes and provide greater strength. Actually, this is unnecessary; in a disaster the spreader arm breakage always occurs right at the edge of the base plate so the reinforcing collars add no additional protection. Moreover, the U bolts will crush the fiberglass tubes only if excessive tightening is applied.
If you would prefer to avoid all ordering of aluminum, flanges, hardware and U bolts, the measuring, cutting and drilling, you can buy a complete base plate already built with all stainless steel components at KIO Technology. The bottom fastening arrangement is a bracket and U bolts which allows several different size mounts.