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Old July 12th 18, 05:19 PM posted to rec.bicycles.tech
AMuzi
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Posts: 13,447
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


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