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drill/tap in frames



 
 
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  #81  
Old July 12th 18, 05:03 PM posted to rec.bicycles.tech
Frank Krygowski[_4_]
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Posts: 6,415
Default drill/tap in frames

On 7/11/2018 11:16 PM, Jeff Liebermann wrote:
.... 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.


Note that your two stated possibilities are not mutually exclusive.

Your logic is a sort of mirror image of the fallacy applied to all sorts
of weird bicycling schemes:

"This makes bicycling a bit safer [or at least, we think so], so
everybody should use it."

And in its worst version: "We must make it mandatory."

--
- Frank Krygowski
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  #82  
Old July 12th 18, 05:11 PM posted to rec.bicycles.tech
JBeattie
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Posts: 3,489
Default drill/tap in frames

On Thursday, July 12, 2018 at 8:05:59 AM UTC-7, AMuzi wrote:
On 7/12/2018 2:31 AM, sms wrote:
On 7/11/2018 8:43 PM, Jeff Liebermann wrote:
On Wed, 11 Jul 2018 17:24:40 -0400, Frank Krygowski
wrote:


Exactly. Strong enough is strong enough.

OK, so let's pretend that the tube with the Rivnut bent at
10% less
tension. Is that "strong enough"? There's no way to tell
without the
original design calculations, or reverse engineering the
frame with an
FEA model. Too bad Autodesk killed their online
ForceEffect web app.
http://blogs.autodesk.com/inventor/2017/01/17/autodesk-forceeffect-family-retirement/

I think I could have modeled the problem using the program.


"Rivnuts are great for low stress areas, but they rely on
expanding in addition to crushing to grip the surrounding
material, therefore a rivnut will impose a tensile stress
around the hole which isn't good news since this will add to
any load stresses, not to mention the concentration effect
brucey speaks of.

I'm not sure there is any place on a bike frame that I'd be
happy to use them. Any time I've needed to attach something
it's been with a properly machined alloy 2-bolt clamp around
the tube with a thin [1mm] thick rubber shim between clamp
and tube."


Why then don't more airplanes fall out of the sky?

https://www.skygeek.com/rivnut-tool.html
http://spenceraircraft.com/hardware/...ivet-nuts.html

from that page:
" Our rivet nuts are manufactured to meet the National
Aerospace Standard. " So much for zero tolerance eh?

With a broken bicycle you could walk home!


The rivnut industry has been hiding the truth for almost a century. See this? https://tinyurl.com/yd5s33m9 Massive rivnut-related failure. Apollo 13? Rivnut. It is so much worse than you know.

-- Jay Beattie.




  #83  
Old July 12th 18, 05:19 PM posted to rec.bicycles.tech
AMuzi
external usenet poster
 
Posts: 9,844
Default drill/tap in frames

On 7/12/2018 10:39 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.


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.

Now all I have to do is find a donor steel frame and a way to bend it
without producing a crimp.


Drivel: The CNC conversion is about 80% done with cables running
everywhere and no way to close the controller box:
http://802.11junk.com/jeffl/pics/CNC-conversion/
Work on the conversion came to a screeching halt when one of the
participants went in for major surgery, and the owner got a big order
that required dropping everything and switching to making parts. The
good part is that it appears that profits from this first job will
more than pay for the cost of the hardware and parts (about $3,000USD
total). We even bought a new VFD that really wasn't needed. The only
problem is that I can't get any machine time to make my toys.


Seamless 4130CrMo aircraft tube is cheap if you want to
pursue it with two sections cut from the same tube.

--
Andrew Muzi
www.yellowjersey.org/
Open every day since 1 April, 1971


  #84  
Old July 12th 18, 05:24 PM posted to rec.bicycles.tech
Frank Krygowski[_4_]
external usenet poster
 
Posts: 6,415
Default drill/tap in frames

On 7/11/2018 11:43 PM, Jeff Liebermann wrote:
On Wed, 11 Jul 2018 17:24:40 -0400, Frank Krygowski
wrote:


Exactly. Strong enough is strong enough.


OK, so let's pretend that the tube with the Rivnut bent at 10% less
tension. Is that "strong enough"? There's no way to tell without the
original design calculations, or reverse engineering the frame with an
FEA model. Too bad Autodesk killed their online ForceEffect web app.
http://blogs.autodesk.com/inventor/2017/01/17/autodesk-forceeffect-family-retirement/
I think I could have modeled the problem using the program.

Maybe this will work:
http://structural-analyser.com
Nope. Won't do tubing.

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.


Yep, but my use of UCSC equipment has turned into a complex hassle.
I'll spare you the details, but at this time, it's not an easy
options.

I was wondering how I would do it on a proper machine. Probably
support the tube at the ends and push in the middle behind the Rivnut.
The problem with that is I'll probably crimp the tube where it's
pushing. It's likely I'll tear the tube before it bends. So, I'm
stuck with securing one end, and pulling (or pushing) on the other.

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.


Good point. However, it will take too many tubing samples to test all
the possible combinations of forces available. Shall we keep it
simple and just bend a tube or two?


Well, it depends on which you want: Test results? Or good and applicable
data?


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.


Clamping action requires equal compression at all points around the
Rivnut hole. That's not going to happen in tubing where the Rivnut is
being crimped onto a curved surface. At the peak of the curve, there
will probably be plenty of compression force holding the Rivnut in
place. 90 degrees to either side, there may be an air gap with zero
compression force. In order to make it stronger on the curved surface
of the tubing stronger, the Rivnut would need a matching curve.


I agree there would be variations in compression around the
circumference of the hole. I doubt that they would be important.

Here's the situation with dozens of details of bicycle design: Because
of the geometric complexities, plus the uncertain and variable loads, we
can't be precisely sure of the stress levels or safety factors. We could
ensure nice high safety factors only by adding considerable weight, but
that's usually undesirable.

So what has happened in practice over the last 150 years? Effectively,
it's been evolution by trial and error. A framebuilder may try a new way
of fabricating (say) the connection of the seat stays to the main frame
tubes, one that saves two ounces. Others notice and wonder if it will
break. If it doesn't break, others copy it. If it breaks, it's not used
again. It's survival of the fittest designs.

These days, some can streamline the trial and error process by use of
FEA. But A) that usually happens only in big firms like Trek, Cannondale
or Specialized; and B) it's still normally done only for main design
features, not for details like Rivnuts.

How does this evolution process apply to Rivnuts? They're used a lot.
They work. They're acceptable. Anything more is Scharfian nonsense or
navel gazing.


--
- Frank Krygowski
  #85  
Old July 12th 18, 05:24 PM posted to rec.bicycles.tech
AMuzi
external usenet poster
 
Posts: 9,844
Default drill/tap in frames

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
poses 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.

--
Andrew Muzi
www.yellowjersey.org/
Open every day since 1 April, 1971


  #86  
Old July 12th 18, 05:26 PM posted to rec.bicycles.tech
Frank Krygowski[_4_]
external usenet poster
 
Posts: 6,415
Default drill/tap in frames

On 7/12/2018 3:01 AM, sms wrote:
On 7/11/2018 8:43 PM, Jeff Liebermann wrote:
On Wed, 11 Jul 2018 17:24:40 -0400, Frank Krygowski
wrote:


Exactly. Strong enough is strong enough.


OK, so let's pretend that the tube with the Rivnut bent at 10% less
tension.* Is that "strong enough"?* There's no way to tell without the
original design calculations, or reverse engineering the frame with an
FEA model.* Too bad Autodesk killed their online ForceEffect web app.
http://blogs.autodesk.com/inventor/2017/01/17/autodesk-forceeffect-family-retirement/

I think I could have modeled the problem using the program.


It's a bad experiment because it doesn't take into account whether or
not the hole was properly drilled and the Rivnut properly installed. You
also have to do it with the same aluminum tubing used on a bicycle
frame, but even then it isn't accurate because there's no way to factor
in metal fatigue which isn't an issue as much in steel as it is in
aluminum.

Remember, just because you can often get away with doing a really stupid
thing, it doesn't mean that you should still do it.


Remember, just because one person declares a practice to be stupid, it
doesn't mean the practice really is stupid.

In fact, if the practice (like the use of Rivnuts) is generally very
successful, the stupidity probably lies elsewhere.

--
- Frank Krygowski
  #87  
Old July 12th 18, 05:31 PM posted to rec.bicycles.tech
Frank Krygowski[_4_]
external usenet poster
 
Posts: 6,415
Default drill/tap in frames

On 7/12/2018 11:54 AM, Jeff Liebermann wrote:
On Thu, 12 Jul 2018 00:41:36 -0700, John B. Slocomb
wrote:
Then, of course, the question arises as to what is a significant
difference? Someone mentioned a bit ago about deciding that a TIG
welded frame joint was strong enough to work, ignoring that a properly
made sweated joint is always much stronger.

Bicycle tubes and thus frames, are not all of the same strength.
Columbus XCR material has an ultimate tinsel strength of 1350 MPa
(195,800 PSI), Nobium is 1050 (152,289 PSI) and 25CRMO4 is 80 MPa
(116,030 PSI).

One can only speculate on the effects of drilling, oh say, a quarter
inch rivnut hole in a (approximately) 200,000 psi strength tube and
doing the same thing in a tube roughly half the strength?


Good point. I plan to use the weakest possible steel tubing as
excavated from the junk pile. I think it unlikely that I'll find any
manner of exotic metals or even double butted tubing. At this time,
all I care about is that the two tubes are reasonably identical.


If you really proceed with this, you should understand that under static
loads, low strength steels are largely unaffected by stress risers.
Their ductility enables microscopic high stress areas to yield and
distribute stress away from the discontinuities.

High strength steels are usually less ductile, so stress risers are more
of an issue. All steels are affected by stress risers in fatigue situations.


--
- Frank Krygowski
  #88  
Old July 12th 18, 05:50 PM posted to rec.bicycles.tech
AMuzi
external usenet poster
 
Posts: 9,844
Default drill/tap in frames

On 7/12/2018 11:26 AM, Frank Krygowski wrote:
On 7/12/2018 3:01 AM, sms wrote:
On 7/11/2018 8:43 PM, Jeff Liebermann wrote:
On Wed, 11 Jul 2018 17:24:40 -0400, Frank Krygowski
wrote:


Exactly. Strong enough is strong enough.

OK, so let's pretend that the tube with the Rivnut bent
at 10% less
tension. Is that "strong enough"? There's no way to
tell without the
original design calculations, or reverse engineering the
frame with an
FEA model. Too bad Autodesk killed their online
ForceEffect web app.
http://blogs.autodesk.com/inventor/2017/01/17/autodesk-forceeffect-family-retirement/

I think I could have modeled the problem using the program.


It's a bad experiment because it doesn't take into account
whether or not the hole was properly drilled and the
Rivnut properly installed. You also have to do it with the
same aluminum tubing used on a bicycle frame, but even
then it isn't accurate because there's no way to factor in
metal fatigue which isn't an issue as much in steel as it
is in aluminum.

Remember, just because you can often get away with doing a
really stupid thing, it doesn't mean that you should still
do it.


Remember, just because one person declares a practice to be
stupid, it doesn't mean the practice really is stupid.

In fact, if the practice (like the use of Rivnuts) is
generally very successful, the stupidity probably lies
elsewhere.


Goes both ways. Sometimes, the crowd looks to The Left
while visionaries look Right:

https://www.zerohedge.com/sites/defa...20nato%204.jpg

Other times the 'different drummer' is trouble:

http://www.latimes.com/local/lanow/l...122-story.html

--
Andrew Muzi
www.yellowjersey.org/
Open every day since 1 April, 1971


  #89  
Old July 12th 18, 06:21 PM posted to rec.bicycles.tech
Emanuel Berg[_2_]
external usenet poster
 
Posts: 1,035
Default drill/tap in frames

Frank Krygowski wrote:

Then you should definitely not just drill and
tap the frame tube itself.


Why not?

--
underground experts united
http://user.it.uu.se/~embe8573
  #90  
Old July 12th 18, 06:37 PM posted to rec.bicycles.tech
John B. Slocomb
external usenet poster
 
Posts: 90
Default drill/tap in frames

On Thu, 12 Jul 2018 10:05:56 -0500, AMuzi wrote:

On 7/12/2018 2:31 AM, sms wrote:
On 7/11/2018 8:43 PM, Jeff Liebermann wrote:
On Wed, 11 Jul 2018 17:24:40 -0400, Frank Krygowski
wrote:


Exactly. Strong enough is strong enough.

OK, so let's pretend that the tube with the Rivnut bent at
10% less
tension. Is that "strong enough"? There's no way to tell
without the
original design calculations, or reverse engineering the
frame with an
FEA model. Too bad Autodesk killed their online
ForceEffect web app.
http://blogs.autodesk.com/inventor/2017/01/17/autodesk-forceeffect-family-retirement/

I think I could have modeled the problem using the program.


"Rivnuts are great for low stress areas, but they rely on
expanding in addition to crushing to grip the surrounding
material, therefore a rivnut will impose a tensile stress
around the hole which isn't good news since this will add to
any load stresses, not to mention the concentration effect
brucey speaks of.

I'm not sure there is any place on a bike frame that I'd be
happy to use them. Any time I've needed to attach something
it's been with a properly machined alloy 2-bolt clamp around
the tube with a thin [1mm] thick rubber shim between clamp
and tube."



Why then don't more airplanes fall out of the sky?

https://www.skygeek.com/rivnut-tool.html
http://spenceraircraft.com/hardware/...ivet-nuts.html

from that page:
" Our rivet nuts are manufactured to meet the National
Aerospace Standard. " So much for zero tolerance eh?

With a broken bicycle you could walk home!


I might be interesting to know that the "rivnut" apparently was first
developed to hold the deicer boots on the leading edge of an
aircraft's wing in 1930, so we can safely say that they have been
successfully used in the aircraft industry for the past 88 years....
strange how they could have been so successful in one industry while
(apparently) a failure in another.
--

Cheers,

John B.
 




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