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#71
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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. |
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#72
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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
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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
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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
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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
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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
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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
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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
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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
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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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