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.