View Single Post
  #74  
Old July 12th 18, 10:42 AM posted to rec.bicycles.tech
John B. Slocomb
external usenet poster
 
Posts: 547
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.
Ads
 

Home - Home - Home - Home - Home