[TowerTalk] Force12 rivets

[Grant Saviers]

One more implementation alternative to add to the stack:

Place the rivets at 90 degrees to each other, two sets of two offset 
along the element at 1/2 the rivet spacing.  The theory is the same as 
using two setscrews to hold a pulley to a round shaft - lockout the 
shaft to bore clearance in two planes.  This is what the ME handbooks 
advise to prevent rocking or fretting on the screw or the shaft to the 
bore.  In the early days, we had pulleys loosen on disk drive spindles 
until this change was made.

When rivets are set at 180 deg from each other or three sets at 120 
degrees the tubing is being distorted to fill the clearance gap at the 
rivet so the tubing must distort outward at another spot.  This is 
minimized with rivets at 90 degrees since the gap being closed is less 
and more tube is free to distort.  Thus, the rivet provides more 
clamping force & friction.  The 90 degree riveted slip fit can't wiggle.

This also avoids more holes/rivets and aligned holes that could weaken 
the elements.

Not much has been said about what type/grade of rivets to use.  What 
experience can be shared about those specs?  There are a lot of choices.

Grant KZ1W


On 2/24/2011 7:27 AM, K8RI on TT wrote:
> On 2/24/2011 8:30 AM, Gary E. Jones wrote:
>> I have a bunch of Force 12 antennas up in the air, all without any problems
>> for years. However, that is probably because a good friend of mine bought a
>> bunch before me, and rather quickly had one of the sections of element tips
>> simply drop to the ground. The preferred method of construction was to have
>> three rivets, all on positioned on the bottom of the element and on only one
>> side of the element. There was enough "play" in the telescoping elements
>> that the rivets would simply gradually be worked by the play until the
>> rivets dropped to the ground and the element sections worked out of their
>> telescoping tubing and drop to the ground also.
>>
>> MY friend (K5JZ) spent a lot of time talking with Force-12 and they came up
>> with the process of using 6 rivets per junction, three on one side of the
>> tubing and opposed by three on the other side of the tubing so they were 180
>> degrees apart. Placing them on opposing sides removed all the very small
>> "wiggle" of the elements and held them firmly in position.
> I "would think" that two or 3 sets at 120 degrees staggered with a 60
> degree offset would give the most secure connection.
>
> BTW I mentioned way earlier in this thread that my force 12's didn't
> have blind rivets, but I discovered the two packages of *spare* rivets
> from force 12 ARE blind rivets.  Not sure why those in it aren't.
>
> OTOH I really don't see as if it'd make much difference. If properly
> seated either type should seal and if not neither type would seal properly.
>
> I don't like the idea of rivets on line 180 degrees apart. It makes a
> good secure connection, but at the expense of the element strength along
> one axis which is admittedly in a low stress area so it probably makes
> no difference. OTOH it would be a good idea to avoid the practice in
> higher stress (or loaded) areas.
>
> 73
>
> Roger (K8RI)
>
>
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