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Re: [TowerTalk] Choice of aluminum

To: K8RI <>
Subject: Re: [TowerTalk] Choice of aluminum
From: Grant Saviers <>
Date: Sun, 14 Oct 2012 18:13:25 -0700
List-post: <">>
Roger, I just unloaded 35k lbs of machines and 10k lbs of crates and shuttled them to my shop, so been there done that re big flat bed truck partially blocking the street at the open end of my dead end. I hope your mill makes nice chips!

Some clarifications -

Re the tolerances of tubing diameters: Tube Service provides drawn Al tube tolerances on their web site, see

For the 1 to 2" od sizes of 6061 or 6063 the numbers are as follows for 0.125" wall:

max single point diameter deviation +/- 0.010"
maximum point wall thickness deviation +/- 10% of wall thickness or +/-0.003" whichever is greater
mean wall thickness deviation +/-0.006"

So if one is lucky, 0.125" wall thickness diameter steps might telescope (at least 0.005" clearance and with plenty of Never-Seez) . In my experience the mills are controlling to "something sigma", maybe not Six Sigma, but tight enough to not draw much scrap. So it's a bad idea to bet against the mill QC department. It would be interesting to know if TT & DXE ask for tighter tolerances as the above numbers could cause their wall thickness to interfere if tolerances are at/near the limits.

Re Boom Lifts: I've had no difficulty renting 45' and below. For a 90' unit I did need to get a rider to my liability insurance with the rental company as a named beneficiary for the $250,000+ machine, since I am not a bonded contractor. The rider was free IIRC. I've rented several times in two states from three rental yards without any more hassle than that. I did manage to get the 2WD 90' unit stuck, but that is another story, and not uncommon. No licenses needed other than a valid credit card. The OSHA placards say persons in the lift need full fall protection so consider your choices even though IMHO the risks are a fraction of those of climbing. The computers in the lift constrain when (wheelbase tilt & boom azimuth) you can elevate and when you can drive with the boom elevated. The (JLG and Genie) controls have "turtle" and "rabbit" modes, almost always "turtle" for me. STAY AWAY FROM POWER LINES! (which I think is the rental yard's number one concern - dead operator, fried machine with boom up, and power outage) The time saved and pain avoidance vs climbing/tramming/hoisting and from retrieving forgotten tools or dropped nuts was huge for me and I felt much safer. My last 40' rental cost (10/2011) was about $420 for a weekend (no charge for Sunday if the used engine time is less than 8hrs), $300 for the machine and $120 round trip on the delivery. (Oh, I can work on problems at the boom end or anywhere on any element - very cool.)

Grant KZ1W

On 10/13/2012 10:52 PM, K8RI wrote:
On 10/13/2012 8:44 PM, Grant Saviers wrote:
DX Engineering sells Yagi-Mech which calculates wind loads for yagi
elements.  Generally, gravity is less stress than wind so you can get
some estimates of what is needed for diameters and wall thickness for a
self supporting vertical.   (zero wind will reveal the gravity stress

A problem with stock tubing from mass metal suppliers is a .250 wall is
.250 +/- some tolerance which may preclude telescoping at the stepped

That's not "May Preclude"telescoping, stepped diameters in half inch steps and 1/4" wall should not fit! Period. If they do fit they are mis sized because the numbers would give you what is called an interference fit. With Aluminum you'd need something like never seize(DP?) and the pieces would have to be pressed together.

A word of warning: I don't know your altitude, but for those who live in more Northern (and Southern climates)and you are next to Argentina... If you machine a piece to fit tightly into the base of the vertical and you live in an area where freezing occurs even on occasion, put in plenty of drain holes. Aluminum and steel are no match for freezing water.

My daughter was down there 6 months ago, ice climbing in Argentina.

 You won't know until you try it for each tube. Note that DXE
(and Texas Towers) sells tube made especially for telescoping and the
walls thickness is reduced appropriately so the draw tolerance can be
accommodated.  I've asked DXE for longer lengths than catalog - no
dice.  Apparently, they have to order mill lots to get the thinner wall
and have it cut to length by the supplier.

Either they or maybe Texas Towers have 12' lengths which must go motor freight and are still only half lengths as standard mill lengths are 24 feet. I've seen the 12 footers advertized with the freight warning.

Normally 12' is plenty long for even 40 meter elements and you can build splices for the boom. The same goes for verticals. You either need a flat bed truck or pick up with pipe racks to move the stuff. I live on a short street that one of the big freight trucks can only back as far as our driveway. There is absolutely no way they can get into the driveway even though its wide and paved. They can't make the turn off the street into the drive. They can barely make the turn onto the street. Also, standard mill finish is not the smooth, shiny, reflective shine we see on the stuff specifically for antennas.

I usually have stuff delivered to the local airport and then hire a tilt bed used for hauling cars and trucks. That's about $80 a shot and considered very cheap. The steel and aluminum suppliers usually deliver via a flat bed for sheet, tube, and plate and do so free for good sized loads or if I'm willing to wait until they have a load headed this way. Of course when you consider the time it took to get the milling machine off the big truck and onto the tilt bed made the expense well worth it. Then I made a platform out of 2 X 12's and used 1" steel pipe rollers under it. It still took me over a full day to get the mill from the front of the shop to the back. I've been running conduit (EMT) from the contactor box to the breaker box for the last two days. I only have one short piece to go from the breaker box to the long run, but it has 3 bends...2 shallow and one 90 degree and bending conduit is not my best suit!. Now I need a "soaper" to feed the cables into the conduit while I pull. Hope to get that done tomorrow, Sunday afternoon.

I may just let the cable hang down to the breaker until I can get to town and pick up another piece of 3/4" EMT.

One of the problems with the big trucks is they completely block the street or road while unloading. There is also the problem of unloading really heavy stuff. They don't like to be setting there while you unload 20 or 30 pieces of tubing

The only way I can get it is mill lots, or wait and get it as part of a lot so I don't have to pay the extra. A mill lot is a lot of tubing.

Also most of the sizes are for antenna elements and are not structurally sound for unguyed verticals.

 I've found that the
"guarantees telescoping" wall thicknesses are hard to find in stock at
Jorgensen, Tube Service, Thyssen, etc., but it is always worth a call as
they can check the entire USA inventory online.  You always have the
choice of machining some couplers from very thick wall material, also
known as Holobar.  The good news is stocks a lot of
sizes and will sell it in 12" lengths.

My former QTH 80m top loaded vertical failed from fatigue after 6 years
since I guyed it at the top and 50% - a bad idea as it oscillated like
crazy in winds greater than 15kts.  So plan to guy at heights that won't
couple oscillations between sections through guy points.  My failure
point was like it was laser cut.  Note that Al has NO threshold fatigue
stress level, whereas steel has a threshold that if not exceeded the
fatigue life is infinite.

Consider what it will take to erect the mast - a 50% height falling
derrick will likely work or a sign truck crane might be able to handle
the weight.

A mast and hand winch for a falling derrick will also work, but it can be slow and tiring.

  Or rent a 40' 4WD boom lift as they usually have 500#
capacity so you and the mast hopefully won't exceed that ;-) .  They're
a lot of fun/exciting and easy if you go slow and get the delivery guy
to give you the basic operating course.

Many companies will not allow any one to operate their equipment other than their employees due to insurance. I used to operate the things where I worked (before going to college) but my license has long since expired. One place locally would let me run theirs, but it was well over $1000 for the week end. Another place 20 miles away was just over half their price, but I had to use their operator and it was "portal to portal" for both the machine and operator.

Grant KZ1W

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