AMuzi wrote:
:On 7/12/2018 10:59 AM, Frank Krygowski wrote:
: On 7/12/2018 11:39 AM, Jeff Liebermann wrote:
: On Thu, 12 Jul 2018 00:22:57 -0700, John B. Slocomb
:
: wrote:
:
: On Wed, 11 Jul 2018 20:16:33 -0700, Jeff Liebermann
:
: wrote:
: Nope. I'm not trying to measure if the tubing is strong
: enough.
: Assuming identical lengths of tubing, I wanted to see if
: the presence
: of a Rivnut significantly changed the tension required
: to bend or
: break the tubing when compared to the identical tubing
: that did not
: have a Rivnut inserted. If I'm able to pull hard
: enough, I should be
: able to eventually break both tubes. If they break at
: the same
: tension, then I'll declare the Rivnuts are safe to use.
: If there's a
: substantial difference in tension, then I'll declare the
: Rivnuts
: weaken the frame.
:
: I'd think it obvious that any hole drilled laterally into
: a tube would
: have an effect on the bending strength of the tube. The
: question
: wouldn't be whether the rivnut changed the strength of
: the tube but
: whether the tube was strong enough with the rivnut
: installed in the
: tube.
:
: Again, I expect some reinforcing effect from the Rivnut's
: clamping action. For an analogy: Did steel frames fail in
: significant numbers when water bottle bosses were brazed on
: and tapped? I doubt it. While a crimped-on Rivnut wouldn't
: add as much strength (as a guess) I think it may add enough
: to get the strength back up to that of the un-drilled tube.
:
: Also, I'm pretty sure a bike down tube sees little if any
: bending stress, except perhaps in a crash. The stresses of
: concern are torsional.
:
:
: Agreed.
:
: Reading between the lines, what others are apparently
: suggesting is
: that even with a hole drilled into the frame, the tubing
: is still
: sufficiently strong to consider the bicycle rideable. In
: other words,
: if the drilling a hole and installing a Rivnut decreased
: the bending
: strength by 10%, I would agree that the hole and Rivnut
: don't pose a
: risk. However, if it decreased the strength by 50%, I
: would consider
: it a hazardous modification. I'm not too sure what to do
: about
: numbers in between or even if the 10% is realistic.
:
: To complicate matters, there's the problem of the notch
: required by
: Rivnuts to prevent rotation. That's a stress riser by
: anyone's
: definition and will probably be the start of any break
: during testing.
: I'll try to position it where it will do the least damage.
:
: The notch is small enough to be enveloped in the crimped
: portion of the Rivnut. I doubt that it's effective as a
: stress riser. Really, I doubt that it feels any significant
: stress, other than compression from the clamping or crimping
: action.
:

:In practice, crashed frame tubes don't deform at the bottle
:bosses. The general truism is that a brazed joint is as
:strong or stronger than the steel tube so a brazed insert
oses no risk. That may not be exactly correct but we work
:with it.

:Some builders at the cusp of change between 'no brazed bits'
:and 'braze every possible thing' fashions (like Galmozzi)
:brazed bolts on the tube and so nuts secured the bottle
:cage. Odd looking but worked as well as anything.

I got a nasty gash from a frame like that. Just picked it up, and cut
myself on the bolt.



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sig 126