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drill/tap in frames



 
 
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  #71  
Old July 12th 18, 08:22 AM posted to rec.bicycles.tech
John B. Slocomb
external usenet poster
 
Posts: 57
Default drill/tap in frames

On Wed, 11 Jul 2018 20:16:33 -0700, Jeff Liebermann
wrote:

On Wed, 11 Jul 2018 13:48:47 -0500, AMuzi wrote:

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?'.


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.




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.


Where are the Rivnuts installed on these machines? Water bottle
holders? The pictures don't show much detail:
https://www.google.com/search?q=Santana+ExoGrid+tandem&tbm=isch&
https://www.google.com/search?tbm=isch&q=bianchi+aluminum

--

Cheers,

John B.
Ads
  #72  
Old July 12th 18, 08:31 AM posted to rec.bicycles.tech
SMS
external usenet poster
 
Posts: 8,299
Default drill/tap in frames

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."
  #73  
Old July 12th 18, 08:41 AM posted to rec.bicycles.tech
John B. Slocomb
external usenet poster
 
Posts: 57
Default drill/tap in frames

On Wed, 11 Jul 2018 20:20:25 -0700, Jeff Liebermann
wrote:

On Wed, 11 Jul 2018 15:46:28 -0700, John B. Slocomb
wrote:

(Big Smile) I know a bike builder who accidentally did just that, with
out the rivnut being installed - bending the curve into the front fork
blades with a 5 foot bar :-)


I think that's called a "torque amplifier".

But as an aside, anything will break given sufficient force applied
which doesn't prove much of anything.


Ah, but if there's a significant difference in tension (force) between
the tube with and without a Rivnut, then methinks it demonstrates that
Rivnuts weaken the frame. I think the real trick will be to find two
tubing pieces that are really identical. I'll check with the local
"Bike Church" to see if they have any old frames laying around. I
have a few frames, but I didn't want to trash them quite yet.


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?
--

Cheers,

John B.
  #74  
Old July 12th 18, 10:42 AM posted to rec.bicycles.tech
John B. Slocomb
external usenet poster
 
Posts: 57
Default drill/tap in frames

On Thu, 12 Jul 2018 00:31:05 -0700, 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.


Interesting this crushing and the imposed tensile stress.

By the way, unless it has changed "tensile stress" is a stress trying
to pull the object apart lengthwise which would sort of indicate that
a rivet, or rev nut, which squeezes against the material it is
installed in can't possible be exerting tensile force against the
parent metal..

Given that aircraft usually have hundreds of rivets holding it
together. All applying the same force as the rivnuts you'd think it
would be crushed into a tiny ball of aluminum :-), although I suspect
that the problem really is that you simply don't know what you are
talking about :-(


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."



That sounds like some sort of hose clamp that you were condemning just
a few minutes ago.

See:
https://www.google.com/search?q=two+...HZa_C0EQsAQIKQ

or
https://www.google.com/search?q=two+...HU4XAjgQsAQIMA


Before you said that they wee a "Kludge" and now you say that you
prefer them?
--

Cheers,

John B.
  #75  
Old July 12th 18, 03:46 PM posted to rec.bicycles.tech
AMuzi
external usenet poster
 
Posts: 9,640
Default drill/tap in frames

On 7/11/2018 10:16 PM, Jeff Liebermann wrote:
On Wed, 11 Jul 2018 13:48:47 -0500, AMuzi wrote:

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?'.


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.

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.


Where are the Rivnuts installed on these machines? Water bottle
holders? The pictures don't show much detail:
https://www.google.com/search?q=Santana+ExoGrid+tandem&tbm=isch&
https://www.google.com/search?tbm=isch&q=bianchi+aluminum



Four pairs of bottle rivnuts on a Santana, two pairs on a
modern road bike.

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


  #76  
Old July 12th 18, 03:57 PM posted to rec.bicycles.tech
AMuzi
external usenet poster
 
Posts: 9,640
Default drill/tap in frames

On 7/11/2018 10:43 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?

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 think this may more apropos of a bicycle frame tube than
tensile testing:

https://www.youtube.com/watch?v=94Bu1DiHOoM

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


  #77  
Old July 12th 18, 04:05 PM posted to rec.bicycles.tech
AMuzi
external usenet poster
 
Posts: 9,640
Default drill/tap in frames

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!

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


  #78  
Old July 12th 18, 04:39 PM posted to rec.bicycles.tech
Jeff Liebermann
external usenet poster
 
Posts: 2,833
Default drill/tap in frames

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.

--
Jeff Liebermann
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
  #79  
Old July 12th 18, 04:54 PM posted to rec.bicycles.tech
Jeff Liebermann
external usenet poster
 
Posts: 2,833
Default drill/tap in frames

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.

Tinsel strength?

--
Jeff Liebermann
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
  #80  
Old July 12th 18, 04:59 PM posted to rec.bicycles.tech
Frank Krygowski[_4_]
external usenet poster
 
Posts: 6,163
Default drill/tap in frames

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.

--
- Frank Krygowski
 




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