[TowerTalk] [Bulk] Re: Shorty Forty Hose Clamp thread

Sun Aug 9 03:59:05 EDT 2015

Having built aircraft, or parts of them with lots of "blind rivets", I 
feel safe is using standard "blind rivets".  The hole needs to be snug, 
clean, and burr free.  I would prefer 4 rivets per joint in sets of 3 at 
120 degrees with the second set of 2 off set from the first set by 60 
degrees.  I'd use good quality, blind rivets, not necessarily aircraft 
"Cherry rivets"  But the Cherry rivets for homebuilts  are not all that 
expensive.
Just make sure the tubing is clean, inside and out.  I've never had them 
come loose.

I purchased a used Force 12 C19XR and WARC7.  After they had been up 
years, the joints were still good.  The rivets were drilled out to 
transport the antennas.  Putting them back together was a quick cleaning 
with fine scotchgard pads, a thin coat of Al noalox and pop rivet back 
together.

73

Roger (K8RI)

On 8/9/2015 12:57 AM, Grant Saviers wrote:
> I'll offer a contrarian view - I don't use hose clamps or rivets. One 
> exception is a pair of hose clamps when the tip of the element is 
> intended to be adjusted e.g. cw to ssb.  Usually a 1/2" to 3/8" tube 
> joint.
>
> Riveted antennas I have acquired and rebuilt had missing and loose 
> rivets.  I drilled the remaining ones out and used 2 bolts/machine 
> screws per joint.  Structurally, pop rivets squeeze a joint together, 
> they don't fill the holes with rivet material.  Bridge rivets (hot 
> forged) and Boeing rivets do fill the hole and prevent motion 
> (airplane rivets are very precise fasteners, essentially each hole is 
> reamed to very tight tolerances and then the rivet is cold forged 
> closed).  A pop rivet allows the tubes to move which eventually 
> loosens the rivet or shears it off and it falls out.  I don't think a 
> pop rivet can achieve the force needed for a "slip critical" joint - 
> https://en.wikipedia.org/wiki/Slip-critical_joint
>
> Hose clamps are for hose, not aluminum and the thread strength is poor 
> (why there is this thread!).  There is no secondary resistance to 
> loosening - no lockwasher, nylock, etc.
>
> I subscribe to the Dave Leeson ("Physical Design of Yagi Antennas") 
> bolt the elements together philosophy, particularly two cross bolts 
> since the bolts tighten against each other as the tubing goes a bit 
> oval from the force.  Nylocks or K-L nuts help keep them from 
> loosening but cross bolted, they do get tight enough to stay tight. I 
> have yet to see one loosen when properly tightened and then 
> re-tightened when the connection stress relaxes over a few days. Cross 
> bolts also restrain the  elements in two planes, just as a pair of 
> orthogonal set screws are best for stuff attached to shafts.  For my 
> 2- 3" center sections I use 5/16-18 and for small 1/2 to 3/8 diameter 
> joints 6-32 works fine, stepping down as needed as element diameters 
> decrease - 1/4-20. 10-32. 8-32.
>
> I use hex head bolts and then socket head (allen) for smaller sizes 
> which are preferable to phillips, although one pro builder who built 
> some of my antennas managed to find hex head #10 and #8 machine 
> screws, but those are pretty rare.  With Penetrox on the threads of SS 
> fasteners and on the overlapped tube sections, disassembly/reassembly 
> with threaded fasteners is simple.  Just did that for seven large 
> yagis that had been up 7 years.  Not a single fastener was loose or 
> missing.
>
> Grant KZ1W
>
> On 8/8/2015 20:19 PM, john at kk9a.com wrote:
>> Hose clamps come in different widths, materials and styles. I am not 
>> sure
>> what MFJ/ Cushcraft uses or what failed for K6UJ, but on my homebrew
>> antennas I use worm drive hose clamps with a 9/16" wide band and a 300
>> series stainless steel screw.  For 1 1/4 or larger tubing I use a 
>> bolt style
>> hose clamp.
>>
>> John KK9A
>>
>>
>> To:    "<towertalk at contesting.com>" <towertalk at contesting.com>
>> Subject:    Re: [TowerTalk] Shorty Forty Hose Clamp thread
>> From:    Robert Harmon <k6uj at pacbell.net>
>> Date:    Fri, 7 Aug 2015 22:02:00 -0700
>>
>> Doug,
>>
>> I no longer use hose clamps after having them strip as you had happen 
>> or the
>>
>> connection
>> loosening after flexing back and forth in the wind (I am also in the 
>> Pacific
>> NW)
>> Now I only use rivets.  I have had a number of Force 12 antennas and no
>> problem
>> at all with the connections.  Their riveted conns sold me.  The HF 
>> beams I
>> have
>> fabbed have riveted elements
>> and no problems.  I wipe on Penetrox when assembling and later when 
>> taking
>> apart
>> the tubing is like new.  Plus to change element lengths it is super 
>> easy to
>> drill
>> out the center of the rivets, they pop right out.  Now I can sleep easy
>> while
>> the winds blow,  hihi.
>>
>>
>> 73,
>> Bob
>> K6UJ
>>
>> _______________________________________________
>>
>>
>>
>> _______________________________________________
>> TowerTalk mailing list
>> TowerTalk at contesting.com
>> http://lists.contesting.com/mailman/listinfo/towertalk
>>
>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk at contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk

-- 

73

Roger (K8RI)

---
This email has been checked for viruses by Avast antivirus software.
http://www.avast.com