GM3WOJ ZL1CT Lattice tower information pages December 2006
Feedback and comments page
Thanks to everyone listed below who responded via the uk-contest e-mail reflector :
From Adrian MW1LCR : I have a local Engineering
Company, who are converting the Post Mounts I have, to Base Plate mounts.
They have quoted me 2-3 Hours labour (at £25 per hour) plus materials (£55)
per Base, all plus VAT. I reckon that's a good deal ! I needed to
find a way to lift tower sections etc and the only way was a pair of
"Steady Legs" and Block and Tackle. This PDF Doc details lots of very
useful info regarding things of this ilk. Including Guy Ropes etc, :
https://atiam.train.army.mil/soldierPortal/atia/adlsc/view/public/8408-1/fm/5-125/fm5_125.pdf (3.93MB download)
From John G4ZTR : I wanted to add a matter of detail
in how my own tower is installed (EP45 BP): I already had a suitable concrete
base, which had supported a previous smaller mast. I was letting the neighbours
get used to the idea, and waiting for a second-hand Versatower to come up for
sale locally, which it did.
The concrete base was large enough (4ft square and 6ft deep) but of course it had no fixings for the new base plate. Following discussions with the manufacturer, about 10 years ago, I purchased some Rawlbolt Chemical Anchors, or Kemfix as they are sometimes called. Forget domestic Rawlbolts, these are 24mm diameter bolts, used by highway engineers to fix safety barriers where alternative fixings are not present.
Drilling four holes 8 inches deep was a real bind, and was difficult using the biggest Kango I could hire locally, but aside from that the fixing is a breeze. And given reasonable temperatures, the chemical sets ready for full load within a hour.
I've used Nylock nuts, and covered the top extremity of exposed thread with a heat-shrink thingy, to lessen the chance of damage or deterioration of the bolt, should I need to undo things eventually.
From Mike VP8NO : Installing a new base plate
mounted FLI HD 12M Versatower. Not sure about the recommendation to have steel
stakes hammered into the sides and base of the hole before pouring concrete.
This is not thought to be a good idea because it allows for corrosion of the
steel within the concrete which can lead to failure and probably adds little or
nothing to the turn over resistance of the base when properly retained within
the ground. All the reading I did, and consultation with a local civil
engineer and government design engineers suggested that steelwork within the
concrete shouldn't be any closer than 75mm to any external surface, with the
exception of the holding down bolts, naturally.
I was disappointed with the length of the bolts supplied, I would like to see them further than 1/3 of the way into the concrete base given that it is only the mass of the concrete above that stops them breaking out. It is common to see in American tower base designs (Rohn) bolts extending at least 2/3 into the concrete mass. Also the FLI design doesn't use any re-bar cage. Re-bar supplies the tensile strength of the mass, concrete itself doesn't have any tensile strength worth considering and with wind forces on the tower, bolts will be in tension which will be transferred to the concrete. However, there must be hundreds of the FLI base design around without problems. I built a re-bar cage which added steel around the high load bolt areas.
I used poly cones over my bolts which are then removed and allow the bolts to move laterally, retained by the wash plates. This allows perfect alignment of the bolts with the mounting plate holes and is shown in the FLI base drawing. The resulting cone shaped holes are then filled with grout. Given that it is easy to make an appropriate bolt setting jig I wouldn't bother going down this route again.
I used a chemical admixture to make the grout slightly expanding, this counteracts the normal shrinkage as the mixture dries and makes for a tight joint both around the bolts and under the base plate.
I also used a vibrator to pack the concrete tightly into the foundation hole when pouring, poking it with a lump of wood isn't
really good enough. I used the same when we poured the footings for our house. It has to be used with care so as not to separate out the concrete mix, only a few seconds at a time.
If you really want to get heavy with the subject, subscribe to the "Tower talk" reflector. American in content but these guys do things big time, 200 foot towers, 4 x array stack, small stuff like that!
Never, never, ever skimp on the concrete. Doing it right means you sleep at night.
On the subject of post mountings. Check out to see if one of the utility companies or contractors has a pole hole borer truck, farmer even. These usually have a huge earth auger which can drill a 14 inch diameter,or there about, hole. Used one of these many years ago to install a base post for an exhibition station tower in Nottingham.
Several of the club were Post Office Engineering (Telecom to youngsters) so we hade the contacts!
If anyone is interested, the expanding grout admixture I used was "Conbex 100" made by Fosroc www.FosrocUK.com You can also get the ready mix grout "Conbextra GP" in 25kg bags. I used "Conbex 100" 'cos it is available in 225g units, much more suitable for air post! One 225g unit is more than enough to add to the grout volume required for a base mount tower unless you make the gap between the base and the block huge. Read the data sheets for mix ratios.
From Ian GM3SEK : 1. To put the reeving
instructions beyond all possible doubt, the raising rope needs to come out above
the third ROUND horizontal brace from the bottom of each section - in other
words, NOT counting the flat bracing at the very bottom.
2. When building up a tower from scratch, each of the telescoping sections can be assembled with its raising rope already threaded through the pulley and out along either side. To prevent the two runs of rope from slumping down and jamming, use cable ties to fasten them neatly alongside the top leg of the tower section, tucked in where there's plenty of clearance. Before lifting the section and sliding it in, pull both ends of rope out in line beyond the top of the section, and keep
some tension on them all the time (e.g. tie them to a line that will drag along the ground, with a brick at the far end). The section will go in with no trouble, and then you can remove the cable ties and carry on as normal.
Though single-handed working shouldn't really be recommended, I had no problem putting in the two sections of a P60 this way.
3. The two angle sections that form the tilt-over rode seem to be welded to the bottom of the ground post in most models - but in some older models they are bolted. If so, those two bolts need to be checked, because together they are handling the same kinds of shear forces as the locking pin. They are high-tensile, obviously, and I think they were originally meant to be 0.5in, but the ones on the BP60 that I inherited were M12, which made them a very loose fit through the holes which were more like 14mm. When I took the bolts out, the middle parts (that cannot be seen) were badly rusted, and necked down to only about 10mm. That is only about 60% of the original area of a 0.5in bolt - gulp! F&L couldn't help, so in the end I had to have some specials turned down from larger HT bolts. That also meant they could be made thicker than 0.5in, and a much firmer fit through the existing holes. Exact dimensions are in the CDXC archives (or anyone who needs them can e-mail me).
Another point is that Ron is currently supplying the Fulton
K1550 winches for the 60ft towers. This model has one less stage of gearing than
the 2550, so the drum rotates in the opposite direction. That means the rope
comes off the outside of the drum, not the inside as it did with the old Pfaff
winches and the 2550.
The main difference is with the raising cable, which goes over the top pulley at more of a sideways angle. It seems OK so far, but there will be a bit more wear, so the pulley could use a washer to keep it away from binding against its bracket.