On 7/11/2018 2:48 PM, AMuzi wrote:
On 7/11/2018 11:42 AM, Jeff Liebermann wrote:
On Tue, 10 Jul 2018 20:41:08 -0700, John B. Slocomb
wrote:

On Sat, 07 Jul 2018 12:33:38 -0700, Jeff Liebermann
wrote:

On Sat, 7 Jul 2018 11:06:52 -0400, Frank Krygowski
wrote:

This group has debated Rivnuts extensively. One poster claims nobody
should install a Rivnut unless he has access to a complete machine
shop.
Others with more experience have said that the installation is easy
for
anyone with normal mechanical skills.

That would be SMS (Steven Scharf) on one of his web pages:
http://nordicgroup.us/cageboss/

Since I've made a mess with all the available technologies, Rivnuts
(steel and aluminum), brazing (steel), TIG (aluminum), and epoxy glue
(plastic boss on aluminum), I'll remain neutral on the matter.

Hint:Â* Use steel Rivnuts on steel frames, aluminum Rivnuts on aluminum
frame, and plastic straps or clamps on CF (carbon fiber).

One can only suppose that those "dumb asses: that manufacture rivnuts
deliberately make their product in a number of materials :-)

I'm not sure about the deliberate part, but yes, one can buy them in
steel or aluminum.Â* I couldn't find any plastic or carbon fiber
rivnuts.

And, it might be added that not knowing what you are doing is not
limited to bicycle maintenence :-)

True.Â* If those expounding on bicycle technology by various electronic
means really knew what they were doing, they would be riding instead
of pounding on the keyboard.Â* If you really want to know how things
work, find someone that is actually doing the work and interrogate
them for the information you need and don't bother reading books,
manufacturers literature, magazines, forums, and newsgroups.Â* The only
downside is that those who really know, tend to be inarticulate and
have difficulties explaining complex concepts, like which way to
tighten a right handed bolt.Â* However, persistence, intimidation, and
perhaps bribery will eventually produce the required answer from a
real expert.

As I mentioned, I have successfully trashed most everything I've tried
to do with Rivnuts on bicycles, and therefore have no opinion on the
matter.Â* However, it might be interesting to try a simple test.Â* I
could probably finance the test by taking bets on the outcome.

Take two identical lengths of steel bicycle tubing.Â* Install a Rivnut
in only one tube at midpoint.Â* Clamp one end in a pipe vise.Â* Pull on
the other end with a Come-Along perpendicular to the tubing.Â* Measure
the force with a load cell.Â* Draw a graph to show when the tubing went
plastic and eventually buckled.Â* Compare results between the tubing
with and without the Rivnut.Â* That should settle the debate whether
Rivnuts are detrimental to frame and stay strength.


I think the question isn't so much 'has the tube's ultimate strength
been diminished?' but rather 'is it yet strong enough for expected
application?'.

Exactly. Strong enough is strong enough.

And BTW, the test you're describing would be much, much easier to do in
a proper tensile testing machine. Find an engineering student, get him
interested, have him get permission to do it as a class project, and
your data would be much better.

But on the other hand, tensile strength of the tube isn't really the
concern. The concern would be fatigue strength, and if we're talking
about the down tube, it would be under repeated, reversing torsional
stresses.

I strongly suspect that you'd find no significant difference. One
feature of the Rivnut is that its clamping action on the parent metal
applies compressive stress. Fatigue cracks start in regions of tensile
stress. The Rivnut may even make the object stronger.

In theory and in absolute yes the tube is less strong. In practice, from
Santana ExoGrid tandems to Bianchi thinwall tempered aluminum models, to
their carbon bikes, rivnuts are not a failure point.

And that's really all you need to know, apart from how to properly
install them. (No, it doesn't require a machine shop.)

--
- Frank Krygowski