I use these U-boöts for booms:
http://www.stauff.com/index.php?id=4022&L=1&MP=3979-3980
The 2" and 3" U-bolts are already with M12 threads.
Their smallest for 20mm pipe is M10!
My boom to mast clamps are M16 (150mm mast size).
And those clamps for the elements:
http://www.stauff.com/index.php?id=3909&L=1&MP=3897-3922
There is also a heavy duty line of clamps which I use on my 40m yagi.
73
Peter, DJ7WW
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of Roger
(K8RI) on TT
Sent: Sonntag, 12. März 2017 21:54
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Booms
Make or purchase saddle clamps. You can make, or have made, saddles, a
pair of which come just short of completely encircling the boom. It's
more weight, but you can make them wide enough for bolt holes. Use two
straight bolts for attachment. They work fine for round or square
booms. Just add a plate under the boom as jim said. I believe DXE
sells a clamp of this type in addition to the standard saddle clamp.
Threaded portion of bolts too long, just saw em off, but crown the ends
on a grind with a fairly fine wheel and don't forget a Thread Chaser
(good insurance) Use galvanized or SS bolts with the proper lube. If
you cut off a galvanized bolt, cover the end with a dab of epoxy, paint,
or even liquid electrical tape. The typical cad plated U-bolt rusts
within a month or two around here, leaving it looking like you used
muffler clamps
This is the first I'd heard of Stauff clamps. Looking them up, they are
the same or similar to the extended saddle clamps I mentioned above made
by Stauff. DXE sells a clamp of this, or similar configuration.They are
not inexpensive, but probably cheaper than having a machine shop make them.
73 Roger (K8RI)
On 3/11/2017 8:59 PM, Grant Saviers wrote:
>
>
> On 3/11/2017 15:12 PM, Jim Thomson wrote:
>> Date: Sat, 11 Mar 2017 09:47:50 -0800
>> From: Grant Saviers <grants2@pacbell.net>
>> To: Jim Thomson <jim.thom@telus.net>, towertalk@contesting.com
>> Subject: Re: [TowerTalk] Booms
>>
>>
>>
>> On 3/11/2017 8:16 AM, Jim Thomson wrote:
>>> Date: Fri, 10 Mar 2017 21:12:43 -0600
>>> To: towertalk@contesting.com
>>> Subject: [TowerTalk] Booms
>>
>> I think you will have a pile of aluminum rubble long before the usual
>> boom bolts fail - eg 1/4-20 for 10 or 15 for 2" booms, 3/8-16 or 1/2-13
>> HDG u-bolts for 20/40 for 3" booms and 1/2-13's thru bolts for machined
>> double saddles 80m 3" booms.
>>
>> ### Typ stauff clamps that are all the rage these days use .25-20
>> SS bolts.
>>
>> Engineering Calculator agrees with your numbers below
>>
>> ## But does ... bending moment = yield strength X section
>> modulus.... still apply to
>> square tubing ??
> >> Yes (but I'm not a structural engineer). However the modulus is
> different on the diagonal, and for the case of 3" sq x 0.125 wall is
> 0.94 in^3 tip to tip vs 1.32 in^3 thru the center in X or Y.
>> Although it might be easier to compress beyond yield stress a round boom
>> with a u-bolt then a square boom with a plate and two bolts. Seen it
>> done. U-bolts are sloppy fits and place all the boom stress at two
>> points - flat boom to element plate and crest of the u-bolt. Why DX Eng
>> saddles or custom made bored split saddles are much superior ways to
>> clamp to booms.
>>
>> ### If its tougher to compress a square boom in the vert plane,
>> it may well be also tougher to bend square tubing in a high wind..
>> like a boom, broadside to the wind ?
>
> >> My concern is only applicable to the point load from a u-bolt on a
> round tube. A thick flat plate clamping a square boom is distributing
> the clamping force over more tube.
>> Channel aluminum is strong
>> stuff, and square tubing is sorta like 2 x channels welded together.
>> Whats even worse is U bolts..and no saddles at all, fubar imo. Typ
>> sheet metal saddles will rust, and are like parallel razor blades.
>> The solid DX eng cast al saddles are the ticket..that plus their
>> extra long .375 inch SS U bolts. Their smaller SS U bolts are .3125
>> and also .25
> >> Standard channel webs are too thin for many applications. Either
> get the thick section version or back them up with a second plate.
> Only works if there enough thru bolts to make them act as a single
> member.
>>
>>
>>
>> 4" x .125" wall tube intuitively to me feels a bit fragile re damage
>> from clamping or handling. Internally sleeving the center of a 3" boom
>> seems to me a better approach than increasing the diameter. Internal
>> sleeving works (ie add up the modulus) for round or square tube per
>> Leeson's analysis. One drawback for 3" and larger is the lack of 0.120"
>> wall, at least I've never found it. So the joiners for long 3" booms
>> need to be machined to slip fit, eg 2.750 x .250 wall turned to
>> something smaller od. btw I have a few to spare of such joiners.
>>
>> ## m2 uses 4.5 inch OD tubing for the boom on their full sized 40m
>> yagis.
>> 4.5 inch OD in the center portion, then 4.0 inch OD for the ends of
>> the booms.
>> I used 4 inch round boom vs 3 inch square tubing for my maths
>> example, since both have
>> aprx the same circumference, no other reason. 4 inch x .125 has a
>> huge section
>> modulus. It also has a lotta windload. 3 inch x .120 wall is ample
>> for most extreme cases.
> >> Internal sleeving is usually a winner. Or adding a second set of
> boom guys as on my 48' x 3" boom 3L 40m. Built by K7ZSD, I know it
> survived some tough wind & ice on an Oregon mountain top before I
> bought it.
>> Perhaps the addition of a short 2.75 x .120 wall internal sleeve,
>> right where the ele to boom
>> assy resides, would provide for extra boom strength. I see that JK
>> antennas does this on their
>> booms. Then it has some meat to it. Once the wall thickness
>> gets to .240 or .250, then its
>> pointless to go any thicker for any boom, or mast. At that point,
>> its better to increase the OD.
>> My chromolly 2.0 x .375 wall mast doesnt hold a candle to a 3.0 x .25
>> wall mast, the section modulus
>> of the 3 x .25 mast is huge vs the smaller diam, but thicker mast...
>> yet both weigh the same, and cost
>> the same.
> >> agree.
>>
>> ## For joining 3 inch x .120 wall boom material, say in the exact
>> center, where the
>> boom to mast plate is, an internal sleeve of 2.75 x .120 wall, say
>> 2- 3-6 ft long, that
>> straddles the center would suffice. The same scheme could be used to
>> splice 3 inch
>> x .120 wall further out from the mast, perhaps with shorter 1-2 ft
>> long internal
>> 2.75 x .120 wall sleeves.
>>
>> ## I see that Dx engineering sells a 48 ft heavy duty 3 inch od
>> boom. Consists of
>> 2 x 24 ft lengths of .120 wall.... with an internal sleeve splice
>> consisting of a 24 ft length
>> of 2.715 OD X .132 wall.
>> https://www.dxengineering.com/parts/dxe-abt3-48
>
> Cool. A new product I think, available the end of March. A bit
> pricey since 3 x 0.125 wall 6061 tube here is about $6/ft. Then
> shipping 24 footers? Plus the crate to prevent damage? Ouch++.
> Strange, I can't make sense of their numbers. Why 2.715" od joiners
> for 3 x .120" tube? That is 0.055" clearance, a lot IMO. Smaller
> tubing slip fits are predicated on 0.010" clearance with 0.120"
> wall. My joiners are nominally 2.736" for 2.750" id or 0.014"
> clearance, perhaps a bit snug. However, I think DXE buys from the
> mill so should know the tolerances and doesn't want anything shipped
> back.
>>
>> ## In any event, the .120 wall 6061-T8 that dx eng sells in every
>> diam from 1.5 inch od...
>> up to 3.0 inch OD, in .25 inch OD increments, is the bomb imo. Then
>> it all just slides together,
>> unlike the .125 wall stuff, which requires that .005 be machined off
>> in a lathe....pita. At least
>> for the hb back yard folks like myself.
> Machining 24" long joiners is not so hard. A bull center and big
> enough lathe dog and a 12 x 36" garage shop lathe can do it.
> Obviously, DXE is having this done from probably 2.750 x something
> tube, but again the numbers don't quite add up since 0.132 wall at
> 2.715 od yields an id of 2.451. Metric or inch that doesn't make
> sense to me if the joiner starts as either 0.1875 or 0.250" wall.
>>
>> Jim VE7RF
>>
>> Grant KZ1W
> >> me again Grant KZ1W
>> _______________________________________________
>>
>>
>>
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73
Roger (K8RI)
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