A mandrel or something inside the tube also helps. A piece of rod with a cross
drilled hole...
On Feb 19, 2011, at 2:19 PM, "Dick Dievendorff" <dieven@comcast.net> wrote:
> I thought a well-aligned V-block and a drill press would be just the thing
> to drill the holes straight. Two drill sizes is fine with me...
>
> Nice summary!
>
> 73 de Dick, K6KR
>
>
> -----Original Message-----
> From: towertalk-bounces@contesting.com
> [mailto:towertalk-bounces@contesting.com] On Behalf Of Grant Saviers
> Sent: Saturday, February 19, 2011 11:48 AM
> To: towertalk@contesting.com
> Subject: Re: [TowerTalk] Force12 rivetstub
>
> If you get on an airplane, you are trusting your life to rivets, some a
> pop rivets.
>
> Here is a manufacturer's website which covers much of the
> engineering. http://www.cherryaerospace.com/
>
> There are a number of issues with screw and hose clamp fastening systems:
>
> 1. As previously posted, screw threads tend to 'worry out holes'.
> 2. As widely noted, hose clamps are not so great - they loosen, in small
> diameters can't be tightened much, increase wind resistance, and create a
> dissimilar metal galvanic cell.
> 3. Not mentioned is the difficulty of drilling holes thru round tubes - a
> big problem with screws and rivets
> a. getting them centered and straight through two tubes (three if
> sleeved for strength)
> b. getting a round hole in thin material
> c. getting a hole that is on diameter - obviously the larger the gap
> between fastener and hole the worse the wear 4. Screws work on clamping
> force generated friction between material layers as well as plain shear
> strength, so how does that work when the tubes can be compressed?
> 5. SS screws also create a galvanic cell.
> 6. Sheet metal screws have so few threads engaged in a thin material so are
> very poor for structural strength.
>
> Aircraft rivet fastening processes use a pilot hole of a smaller than rivet
> outside diameter followed by piloted core drill which acts much like a
> reamer. This provides a hole that is really round and very close to a
> diameter tolerance of less than a couple of 'thou. You can't do that with a
> standard twist drill. The rivet then expands to fill the hole, (minimum
> 'worry") brings the layers being fastened in tight contact (increased
> friction) , and provides clamping force that doesn't rely on compressing a
> tube (constant over time). Either the rivet is solid and bucked from the
> reverse side so its full diameter provides shear strength or a "pop" rivet
> is used that provides the body shear strength of the Al plus the retained
> pull core which can be of several different materials (steel, Al, SS,
> Monel).
>
> Why 3 rivets? Redundancy is good. Spreading the load is good. The tubing has
> clearance so it telescopes and tightening it to ONE side is good.
> The first rivet hole, if drilled and riveted then guarantees the inner
> tube(s) won't move when drilling holes 2 & 3.
>
> What is the downside of rivets? - care and the right drill are needed to get
> holes on size and round. Home-Depot rivets are not a good choice.
> A tool is needed to install them properly.
>
> So are rivets a process "do not try this at home"? - NOT. While aircraft
> piloted core drills are often available on ebay, DeWalt makes a drill which
> works extremely well - pilot point drills. (formerly Black and Decker
> Bullet Drills) They produce holes in thin materials that are round and very
> close to drill diameter using a drill press, and if care is used in a hand
> drill. Many suitable structural grade pop rivets can be set using a quality
> hand tool.
>
> My scratch build 40m Moxon is going together with rivets.
>
> Grant KZ1W
>
> On 2/19/2011 10:36 AM, Chet wrote:
>> Yesssssssss!
>>
>> -----Original Message-----
>> From: towertalk-bounces@contesting.com
>> [mailto:towertalk-bounces@contesting.com] On Behalf Of Gene Fuller
>> Sent: Saturday, February 19, 2011 12:52 PM
>> To: Dick Green WC1M; towertalk@contesting.com
>> Subject: Re: [TowerTalk] Force12 rivets
>>
>>
>> Assuming one rivet is strong enough to do the job the fact that they
>> use three would indicate to me that not even the manufacturer doesn't
>> trusts them. Perhaps a second for backup, but three.....? I would
>> guess that cheaper is the answer. Lets get on with it - past time to cut
> the thread.
>>
>> ----- Original Message -----
>> From: "Dick Green WC1M"<wc1m73@gmail.com>
>> To:<towertalk@contesting.com>
>> Sent: Saturday, February 19, 2011 12:07 PM
>> Subject: Re: [TowerTalk] Force12 rivets
>>
>> snip
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