But thankfully it wasn't worse.
As a quick followup to the post on repairing my antenna, I ran into a problem trying to complete the work today. The bracket went up fine and appears to be secure. I ran into a problem with the tower itself.
I was too busy to grab a photo of the damage, but I found a six year old picture from when I installed my new counterpoise pipe that supports the weight of (and torque from) the tower as it gets cranked over. This will help explain the problem.
The tower, like most towers, is a triangular design; it has three main vertical members and those are connected by a matrix of smaller tubes. The three vertical elements are the interface to the concrete pad. The base is aligned with a factory installed hinge on the north end of the pad so the north side of the tower aligns with east/west. On the south end, there's a single leg and it has hardware built on that attach it to fastener in the concrete pad.
The vertical members are approximately 1-1/2" OD; the smaller tubes are
approximately 1" OD. Highlighted in red is the anchor to a bolt in the
concrete pad. The damage here is that as the tower blew in the winds
with the house bracket broken, that south leg with the right angle aluminum piece
bolted to it bent. That round tube is now kind of oval in cross section, and points a
little to the left. As a result, the tower doesn't "want" to stand
vertically on the mount. It leans left in front of the house bracket.
So now what? I'm not really sure. All of this repair work has been a stretch for my skill set, and this is a bigger stretch. I have some steel stock that I can put into that leg to try to restore more roundness and straighten it out, but I've never tried to do something like that. I don't have an anvil or anything that can support the metal while I bang on it, so I'm still trying to figure out alternatives. I could put something under that leg that keeps it from being bolted down but lines the tower up with the bracket better. Extending that bolt in the slab, so that I could secure that point with the leg standing on something, doesn't seem feasible though.
In brief: bore an 1-1/2" hole in a square piece of steel. Then cut the square in half leaving 2 semi-circular 'dies'. Then use a large C clamp to squeeze your tubing round again.
ReplyDeleteMe Again: another variation would be to use a large enough piece of square/rectangular steel to allow thru holes and then use bolts and nuts to provide the clamping force.
DeleteI like that. I have a roughly 4" long by 2" square piece of cast iron, and I'm relatively sure I have a roughly 1" thick slice of it already available. A little drilling and boring to diameter and I'm there.
DeleteThanks.
Me again: Cast iron may be too brittle for this application. However a couple of thick steel back-straps may help to keep the cast iron in compression. Lubing the die surfaces will help reduce the clamping force a little. An alternative to lubing would be to carefully warm the tubing up a couple of hundred degrees to help persuade it back into shape. If aluminum tubing be careful heating it.
DeleteMakeitfrommetal.com has a writeup on annealing aluminum and how to get the right temperature.
DeleteI have more questions than answers, but perhaps the questions will be helpful. Will annealing the damaged leg make it any weaker than the existing damage? Could you just anneal the sharper curves of the oval section, and hope that work hardening as you reshape it will restore the needed strength?
I see a "small tailpipe expander" on Amazon that you might be able to use to apply tension, then use a mallet to work the high spots down.
I feel like I know just enough to be dangerous...
Jim_R
Jim_R The last two characters in 6061-T6, the aluminum alloy they use, references the thermal treatment the alloy gets that gives the metal it's properties, so thermally treating it without knowing what I'm doing scares me, too.
DeleteWhile a lot of guys have talked about saving their aluminum chips and melting them to cast things, I don't know how they ensure the properties of the alloy they're making. Especially if the chips are from several different alloys of aluminum.
No, a couple of hundred degrees, not 400 or 500. 200 to 250 will not change the temper. This is boiling water temperature.
DeleteFour 5/8" bolts with greased threads will make a lot more clamping force than one 1,200 pound c-clamp. https://www.almabolt.com/pages/catalog/bolts/tighteningtorque.htm says 5/8-11 grade 5 bolts will give a clamp load of 14,400 pounds each.
ReplyDeleteTapered plug the size of the tube ID. Tap it in. Drill thru.
ReplyDeleteAdd a drainage hole through it just in case.
That was my first thought. I started looking for something tapered lying around, but I've got nothing like that. The tube is thick walled - 1.5 OD with .065 walls (1.37 ID) according to a drawing I found on their website. Since I'd think a 1/16" wall would be more likely, I need to go measure.
DeleteI have a scrap piece of round 1.25" steel bar that has been milled a bit on one side, so it's not round anymore. That's what I was considering putting into the tube and hammering on. I think that's too loose.
While not a HAM myself, my brother was part of the MARS network. I acquired a few sections of tower from him a while back, excess to him. Steel tubing where you speak of aluminium. I disagree with locating the hinge at ground level, I would locate it at least a foot above, maybe more.
DeleteBe that as it may, to repair the present problem, perhaps trimming back a foot or so and using a pipe nipple or a conduit nipple as a "splice". There is a type of conduit called "IMT" that is heavier than thinwall (EMT) but not as heavy as "rigid (Sched 40)". I have never used it, I'm an "old school" electrician.But IMT is available at my local HD. Conduit is essentially pipe that has been reamed. IMT will be the same OD as rigid, with a larger ID.
Perhaps a larger size will mate with your tower sections. In the distant past, I have repaired a motorcycle frame with split pipe and screwdriver clamps. It was wasn't very pretty but got me across a couple of states.
As Anonomous suggested a tapered mandril can be used to round the tube end by driving it into the oval ended tower leg, and leaving it in place. Then drill for the cross bolt and presto ! The weep hole in the mandril is a good idea. You can taper a chunk of hot rolled steel rounds of sufficient length in your lathe to make the mandril.
ReplyDeleteAs far as the tower house bracket goes it is unclear to me what wooden roof structure you were anchored into. Is it the Fascia board or the end grain of the roof trusses the tower bracket is lag bolted into ? Neither may be sufficient for the loads encountered by the lag bolts at high wind loads by the antennas. The roof truss structure is mostly nailed, and fascia boards are most certainly nailed to the trusses. Fascia board rarely exceeds 1 inch thickness. Using the published antenna wind load factors and the length of the fulcrum created by the tower a reasonable idea of the forces the lag bolts will encounter. And Nails are not good where pull out resistance is required. The Aluma Tower company has a sound tilt over/ support design. 4 inch steel pipe in schedule 40 aint cheap today from steel suppliers but perhaps theres a scrap yard in your area that has what your looking for. Steel I beam, or square tubing would work in place of pipe.
Some References:
WOODEN TRUSS DESIGN:
https://www.constructiontuts.com/roof-truss/amp/
LAG BOLT PULLOUT RESISTANCE:
https://www.engineersedge.com/calculators/lag_screws_in_wood_pullout_resistance_15390.htm
Thanks for those two links.
DeleteAbout the bracket. The fascia board isn't load bearing; it's drilled out for the unthreaded shoulders of the lag bolts. I believe - but don't know for absolute sure - that the bolts fasten basically into end grain. The only question is exactly where in the end of the roof truss they're anchored. When I put in the new lag bolts, I had re-drilled the holes for the new 1/2" bolts, but the recommended size drill was 5/16 and since the previous bolts were 3/8, the drilling was only for the very end of the hole - about the last 3/4". The bolts felt properly tight to me while installing the bracket.
Again, I'm thinking of this as a temporary fix.
Bear in mind that while the tower has been fine, and the tower, bracket, and all have been through several named hurricanes up to Category 3 since I first installed it around '90, for all of the hurricanes, I cranked over the tower and removed the antennas, leaving just the naked tower standing and held by the house bracket. The tower itself offers very little wind resistance. This was a tropical storm, and the first time I didn't pull the antennas off. We've had other tropical storms, and I'm sure that for some of them, the antennas were up.
6061 t6 has excellent weldability. Do you have an aircraft welder in your area that could do a repair?
ReplyDeleteThe deformation makes the screw-down leg too short to make the antenna stand plumb?
ReplyDeleteIf that is what has happened, then shims could be the answer. Leave the deformation as it is, rather than weakening it (or risking cracking the aluminum) and adjust beneath it.
If the tower is leaning across the hinge point (meaning the single screw down one elongated) cut that leg off enough to let you shim back to level.
If the tower has leaned towards or away from you from the picture taking position, there is more damage than a single distorted tube.
If your system took this much force, a very in depth inspection might be in order.
The lean is toward the left in that picture, toward the (now) shorter leg, not toward the camera. The way I tried to put it in place was to put a lever under the far side of the tower and press down (had my wife stand on it) to rotate it toward the right. I could put a shim under that leftmost leg, but the bend in that leg kept the angle aluminum above the concrete, and I didn't have a way to still anchor it to that bolt sticking out of the concrete.
DeleteI see two main issues in the photo.
ReplyDelete1. The truss tube is bent and has crushed at the anchor clip.
2. The anchor clip can be fastened to the anchor bolt, or the truss tube, but not both when the tower is vertical.
Are you able to tilt or lay down the tower while you work on the end?
Possible solutions
1. Add a liner/spacer inside the flattened tube. The goal is to support the damaged tube and keep it from crushing further when you torque the horizontal bolt. Buy some aluminum tube from McMaster Carr. They have some 1.315 OD X .133 or .179 wall tube in 12” lengths. Cut off 2-4 inches of the smaller tube and push it into the damaged one. Cross drill through the liner using the existing hole as a guide. Insert a bolt as a temporary alignment tool. It would be bad if the inner tube rotated while you did the other work.
2. Angle clip. Replace the old one and fab a new one.
A. Use a cutoff wheel on an angle grinder to cut the existing bolt flush with the concrete pad. Buy two new concrete anchor bolts that are the same diameter. I’m not sure how long they should be, but the more engagement with the concrete the better
B. Buy a new piece of angle from McMaster Carr, 6-12” long. You will want the same leg length, thickness, and material as the current part. It looks like 2x2x1/4 or 3/8.
C. Drill two holes in one leg of the new angle. Use the same diameter as the concrete anchor bolt or maybe a 1/16th over for some tolerance. Put this side down on the concrete and position the new clip roughly where the old one was,
D. Tip the tower back to vertical, and use shims under the bent leg plus temporary guy lines to get it stable while you work.
E. Center the new clip on the leg and mark the concrete at the anchor bolt holes.
F. Move the clip out of the way and use a hammer drill to make new bolt holes in the concrete. Refer to the anchor bolt instructions for the correct size. You may be able to rent a hammer drill and bit for a few hours.
G. Install the new bolts and the new clip. Torque down the nuts.
H. Use the horizontal hole in the tower leg as a guide to drill through the vertical leg of the new angle clip. Match the hole diameter.
I. Insert a new bolt through the tower leg and the angle clip. Tighten the nut so that the tower is stable.
J. Remove any shims or temporary guy lines.
Hoping you come back to see if I left any responses. If so, please go to email, SiGraybeard at gmail dot com with the usual substitutions.
DeleteIn short answer/short summary. First, the tower cranks over and is at about 30 degrees to the ground. I could get a bit lower, but the number is a good approximation. I have plenty of room to work.
My initial attempts at making the tube round again - or at least lots rounder - had some effect but after I broke the second big C-clamp I was using, I stopped working on it. The bent section is still bent, but the tube above and below it are a somewhat better profile.
I started where the tube was closer to round and worked the tool closer to the bent and very out of round section until I broke both a 4" and a 5" C-clamp. The 4" clamp is bent such that it barely closes and the other I had to cut the bolt to get it unstuck. I was using a 1' length of small pipe to get more leverage on the clamp bolt and the handle bent 90 degrees. I might have been able to hammer that off the leg, but thought about that too late.
That probably puts me back at the stage of either cutting off the bottom two inches of that leg and then trying to extend the tube with some other pipe as you suggest, or first trying to pound something tapered into that pipe and both round and straighten that leg.