[TowerTalk] HBDX 48

[Nick Pair]

As the once proud owner of a HBDX 48 (still up just not too proud now) I have a few tips about this beast.
  1; Think about replacing existing bolts with heavy galvanized (these are the architectural grade that require nuts over sized to fit) or stainless steel bolts of the same grade. The original had rust starting in less than a year, in my environment anyway.
  2. Torque the bolts with a torque wrench with no lubricant on threads or nut face. 
  I had failure at the connection between the second and third sections. The holes on one leg elongated mid winter and before I could get to it to splint it, it actually tore the bottom 2 inches off the third section leg. As you probably know the legs are just a rather light gage sheet metal and seem to be not a particularly high strength steel.IMHO
  3. The sheet metal is galvanized before shearing and bending leaving the edges sharp and only protected from rust by the sacrificial effect and whatever zinc is smeared by the shearing edges. Maybe painting with a zinc rich paint could extend life. Some sections of my tower have rusted a lot more than others.
  4. The cross braces are riveted to the legs with aluminum rivets. Think about this and any torque moments you are applying to the tower. Mine hasn't failed but I personally know of several that failed, one with personnel on it.
  5. Some type of bearing or sleeve needed at top. Again here is a place where just thin sheet metal is used and the holes tend to enlongate if mast/boom combination get very large. In my case i used a two foot piece of rigid conduit (GRC) and a floor flange with four bolt holes. I also used a diagonal brace from the top of the stub to each top of leg using the prepunched holes there to attach to tower. The slightly larger than 2 inch I.D. allows plenty of room for a strong mast. The only antenna I ever had on it was a 24 foot home brew 6 mtr. 6L a foot above stub sleeve. That and a 16x16x6 junction box 18 inches from tower top was all the load on tower prior to failure at 2/3 section.
   
  To keep the tower from further destruction all I was able to do was to put a guy wire out from the failed leg at the 3/4 junction to keep the tower from rocking in the wind and coming down. I now need a crane to remove, as I can't find someone dumb enough to climb the tower and gin pole it down. ;-)
  Climbing this type of tower is an exercise in minimumizing the number of cuts from sheared parts and no horizontal members. Leather gloves and shoes a minimum.
   
  May better planning than I used bring you luck on your installation.
   
  73
  Nick
  WB7PEK

 		
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