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#121
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drill/tap in frames
On 7/14/2018 2:01 AM, John B Slocomb wrote:
On Fri, 13 Jul 2018 20:53:33 -0500, AMuzi wrote: On 7/13/2018 8:14 PM, Ralph Barone wrote: John B. Slocomb wrote: On Fri, 13 Jul 2018 12:49:33 +0000 (UTC), Ralph Barone wrote: John B. Slocomb wrote: On Fri, 13 Jul 2018 00:10:02 +0200, Emanuel Berg wrote: James wrote: Then you should definitely not just drill and tap the frame tube itself. Why not? The material is too thin. Is it more thick at the bottom of the bottom bracket shell and at the bottom-mid section of the down tube where I have seen this numerous times, and also the chainguard stays to the chainguard intersection? A bottom bracket is usually specified as 7 - 8 mm thick. -- Cheers, John B. Maybe 3-4 mm. Are you quoting the difference between the OD and ID, or the wall thickness? I just looked at their catalog which red, for example: "LB100R - For 22.2mm Chainstays. 60.30x62.30x7\ufffd. No guides or cut-outs". or "LB109R - With Oval 30x17mm. Chainstays. Angles 60x64x7.30\ufffd. No guides or cut-outs." Given that the first two numbers were obviously length and breadth assumed the last was thickness. Not so? I don't know. I just thought that 7mm wall thickness for a bottom bracket shell appeared to be overkill to me. I did some web searching and nobody publishes data on the OD of bottom bracket shells (probably because it doesn't matter to a first approximation). However, looking through a bunch of diagrams, I did see that many of them had a 7mm deep pocket to hold the bearings. Perhaps that's where your 7 came from. Aha! This BB shell has a 38 mm OD and a 1.370" ID, which gives about 2mm wall thickness. https://framebuildersupply.com/produ...od-made-in-usa Say that again, slowly. The O.D. is 38mm and th I.D. is 1.370?? Just measured a cast 1982 Cinelli and an unknown vendor on a 1978 Bianchi Superleggera at 3mm. Both are m36x24 on vintage frames being repaired. A new mid-1970s RFG pressed shell is 3mm. A new 1976 Nikko Sangyo pressed shell is 4mm but heavy and klunky in other aspects as well. Both 1.370"x24. That's a quick check with a vernier so depending on your purpose you might subtract thread depth. Or not. Regarding threaded holes, I've seen a lot of drilling, piercing, slots, tapped holes and so on on every kind of steel BB without notable failure attributable to that. They do break, just not from holes in the bottom. Classic British bikes have a coarse threaded hole on top LH for a bearing oiler. Cracks don't form around those either. Say that again, slowly. The O.D. is 38mm and th I.D. is 1.370?? That would be 38mm overall, 34.8mm at thread peaks or ~33.8 at thread root leaving about 4+mm dia or 2+mm at the radius theoretically. Which comports roughly with actual measurements yesterday. Surely not 7mm on any modern (not cast iron) threaded BB shell. -- Andrew Muzi www.yellowjersey.org/ Open every day since 1 April, 1971 |
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#122
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drill/tap in frames
On Sat, 14 Jul 2018 08:23:09 -0500,
AMuzi wrote: On 7/14/2018 2:01 AM, John B Slocomb wrote: On Fri, 13 Jul 2018 20:53:33 -0500, AMuzi wrote: On 7/13/2018 8:14 PM, Ralph Barone wrote: John B. Slocomb wrote: On Fri, 13 Jul 2018 12:49:33 +0000 (UTC), Ralph Barone wrote: John B. Slocomb wrote: A bottom bracket is usually specified as 7 - 8 mm thick. Maybe 3-4 mm. Are you quoting the difference between the OD and ID, or the wall thickness? I just looked at their catalog which red, for example: "LB100R - For 22.2mm Chainstays. 60.30x62.30x7\ufffd. No guides or cut-outs". or "LB109R - With Oval 30x17mm. Chainstays. Angles 60x64x7.30\ufffd. No guides or cut-outs." Given that the first two numbers were obviously length and breadth assumed the last was thickness. Not so? I don't know. I just thought that 7mm wall thickness for a bottom bracket shell appeared to be overkill to me. I did some web searching and nobody publishes data on the OD of bottom bracket shells (probably because it doesn't matter to a first approximation). However, looking through a bunch of diagrams, I did see that many of them had a 7mm deep pocket to hold the bearings. Perhaps that's where your 7 came from. Aha! This BB shell has a 38 mm OD and a 1.370" ID, which gives about 2mm wall thickness. https://framebuildersupply.com/produ...od-made-in-usa Say that again, slowly. The O.D. is 38mm and th I.D. is 1.370?? The I.D. is given in inches, so the two dimensions definitely look odd together. That would be 38mm overall, 34.8mm at thread peaks or ~33.8 at thread root leaving about 4+mm dia or 2+mm at the radius theoretically. Which comports roughly with actual measurements yesterday. Surely not 7mm on any modern (not cast iron) threaded BB shell. I suppose it's possible that tandem bottom bracket shells can be thinner walled because the eccentric provides some strength, but somehow I doubt they actually are. At any rate, I just measured (roughly) the wall thickness of my two tandem BB shells and the 1986 Rodriguez (aluminum) is about 4 mm, and the 2012 Santana (titanium) is somewhat less--maybe 3.5 mm. Relating to the original topic, neither has any holes drilled in the seat stays or the chain stays. The Santana has some kind of reinforcement (maybe like the Rivnuts that have been discussed?) at the water bottle cage holes in the frame tubes (down tube and both laterals). -- Ted Heise West Lafayette, IN, USA |
#123
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drill/tap in frames
On Sat, 14 Jul 2018 15:52:39 +0000 (UTC), Theodore Heise
wrote: On Sat, 14 Jul 2018 08:23:09 -0500, AMuzi wrote: On 7/14/2018 2:01 AM, John B Slocomb wrote: On Fri, 13 Jul 2018 20:53:33 -0500, AMuzi wrote: On 7/13/2018 8:14 PM, Ralph Barone wrote: John B. Slocomb wrote: On Fri, 13 Jul 2018 12:49:33 +0000 (UTC), Ralph Barone wrote: John B. Slocomb wrote: A bottom bracket is usually specified as 7 - 8 mm thick. Maybe 3-4 mm. Are you quoting the difference between the OD and ID, or the wall thickness? I just looked at their catalog which red, for example: "LB100R - For 22.2mm Chainstays. 60.30x62.30x7\ufffd. No guides or cut-outs". or "LB109R - With Oval 30x17mm. Chainstays. Angles 60x64x7.30\ufffd. No guides or cut-outs." Given that the first two numbers were obviously length and breadth assumed the last was thickness. Not so? I don't know. I just thought that 7mm wall thickness for a bottom bracket shell appeared to be overkill to me. I did some web searching and nobody publishes data on the OD of bottom bracket shells (probably because it doesn't matter to a first approximation). However, looking through a bunch of diagrams, I did see that many of them had a 7mm deep pocket to hold the bearings. Perhaps that's where your 7 came from. Aha! This BB shell has a 38 mm OD and a 1.370" ID, which gives about 2mm wall thickness. https://framebuildersupply.com/produ...od-made-in-usa Say that again, slowly. The O.D. is 38mm and th I.D. is 1.370?? The I.D. is given in inches, so the two dimensions definitely look odd together. :-) I believe tat the first demension is more then likely to be a thread demension :-) That would be 38mm overall, 34.8mm at thread peaks or ~33.8 at thread root leaving about 4+mm dia or 2+mm at the radius theoretically. Which comports roughly with actual measurements yesterday. Surely not 7mm on any modern (not cast iron) threaded BB shell. I suppose it's possible that tandem bottom bracket shells can be thinner walled because the eccentric provides some strength, but somehow I doubt they actually are. At any rate, I just measured (roughly) the wall thickness of my two tandem BB shells and the 1986 Rodriguez (aluminum) is about 4 mm, and the 2012 Santana (titanium) is somewhat less--maybe 3.5 mm. Relating to the original topic, neither has any holes drilled in the seat stays or the chain stays. The Santana has some kind of reinforcement (maybe like the Rivnuts that have been discussed?) at the water bottle cage holes in the frame tubes (down tube and both laterals). Not much detail for the frame except that they are made from Columbus Spirit-Niobium 6/3/6 tubing which is high end, low weight, tubing. I would guess that the frame holes were probably reinforced with something like http://www.framebuilding.com/Bosses.htm, ART.472 with maybe an additional ART.361 or 367. Certainly not a revnut in that type of frame :-) A useful reference is http://www.framebuilding.com/ as it shows a great many of the usual frame making bits and pieces. |
#124
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drill/tap in frames
AMuzi wrote:
: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 oses 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. I got a nasty gash from a frame like that. Just picked it up, and cut myself on the bolt. -- sig 126 |
#125
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drill/tap in frames
On 7/14/2018 10:20 PM, David Scheidt wrote:
AMuzi wrote: :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 oses 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. I got a nasty gash from a frame like that. Just picked it up, and cut myself on the bolt. Yet another bicycling injury! -- - Frank Krygowski |
#126
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drill/tap in frames
On Sun, 15 Jul 2018 11:06:37 -0400, Frank Krygowski
wrote: On 7/14/2018 10:20 PM, David Scheidt wrote: AMuzi wrote: :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 oses 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. I got a nasty gash from a frame like that. Just picked it up, and cut myself on the bolt. Yet another bicycling injury! Obviously not wearing a helmet. |
#127
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drill/tap in frames
On 7/15/2018 11:50 AM, John B. Slocomb wrote:
On Sun, 15 Jul 2018 11:06:37 -0400, Frank Krygowski wrote: On 7/14/2018 10:20 PM, David Scheidt wrote: AMuzi wrote: :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 oses 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. I got a nasty gash from a frame like that. Just picked it up, and cut myself on the bolt. Yet another bicycling injury! Obviously not wearing a helmet. I saw a head injury yesterday. After eating lunch on a backyard deck, a good friend pushed his chair back from the table and tumbled backwards off the deck. He hit the back of his head pretty hard on the brick walkway, hard enough that he applied an ice pack for 15 minutes. He's not a cyclist. Still, too bad he hadn't worn a helmet. If he had, it _obviously_ would have saved his life. -- - Frank Krygowski |
#129
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drill/tap in frames
On Sun, 15 Jul 2018 20:19:21 +0000 (UTC), Theodore Heise
wrote: On Sat, 14 Jul 2018 18:48:20 -0700, john B john wrote: On Sat, 14 Jul 2018 15:52:39 +0000 (UTC), Theodore Heise wrote: On Sat, 14 Jul 2018 08:23:09 -0500, AMuzi wrote: On 7/14/2018 2:01 AM, John B Slocomb wrote: On Fri, 13 Jul 2018 20:53:33 -0500, AMuzi wrote: On 7/13/2018 8:14 PM, Ralph Barone wrote: John B. Slocomb wrote: On Fri, 13 Jul 2018 12:49:33 +0000 (UTC), Ralph Barone wrote: John B. Slocomb wrote: A bottom bracket is usually specified as 7 - 8 mm thick. Maybe 3-4 mm. Are you quoting the difference between the OD and ID, or the wall thickness? I just looked at their catalog which red, for example: "LB100R - For 22.2mm Chainstays. 60.30x62.30x7\ufffd. No guides or cut-outs". or "LB109R - With Oval 30x17mm. Chainstays. Angles 60x64x7.30\ufffd. No guides or cut-outs." Given that the first two numbers were obviously length and breadth assumed the last was thickness. Not so? I don't know. I just thought that 7mm wall thickness for a bottom bracket shell appeared to be overkill to me. I did some web searching and nobody publishes data on the OD of bottom bracket shells (probably because it doesn't matter to a first approximation). However, looking through a bunch of diagrams, I did see that many of them had a 7mm deep pocket to hold the bearings. Perhaps that's where your 7 came from. Aha! This BB shell has a 38 mm OD and a 1.370" ID, which gives about 2mm wall thickness. https://framebuildersupply.com/produ...od-made-in-usa Say that again, slowly. The O.D. is 38mm and th I.D. is 1.370?? The I.D. is given in inches, so the two dimensions definitely look odd together. :-) I believe tat the first demension is more then likely to be a thread demension :-) That would be 38mm overall, 34.8mm at thread peaks or ~33.8 at thread root leaving about 4+mm dia or 2+mm at the radius theoretically. Which comports roughly with actual measurements yesterday. Surely not 7mm on any modern (not cast iron) threaded BB shell. I suppose it's possible that tandem bottom bracket shells can be thinner walled because the eccentric provides some strength, but somehow I doubt they actually are. At any rate, I just measured (roughly) the wall thickness of my two tandem BB shells and the 1986 Rodriguez (aluminum) is about 4 mm, and the 2012 Santana (titanium) is somewhat less--maybe 3.5 mm. Relating to the original topic, neither has any holes drilled in the seat stays or the chain stays. The Santana has some kind of reinforcement (maybe like the Rivnuts that have been discussed?) at the water bottle cage holes in the frame tubes (down tube and both laterals). Not much detail for the frame except that they are made from Columbus Spirit-Niobium 6/3/6 tubing which is high end, low weight, tubing. Um, no. I did mention (in the previous paragraph) that it is a titanium frame. Then it obviously isn't a "Columbus Spirit-Niobium" frame :-) ... I would guess that the frame holes were probably reinforced with something like http://www.framebuilding.com/Bosses.htm, ART.472 with maybe an additional ART.361 or 367. The ART 475 (Thin Head) looks like what's on the bike. Certainly not a revnut in that type of frame :-) I'm not surprised, I was just guessing--hence, the question mark. |
#130
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drill/tap in frames
Today I measured the three contact points of
a typical chainguard for standard steel bikes, with a caliper. All of the contact points are threaded holes with no nut on the other side. The front and rear stays, which I suppose are welded to the frame, and painted in the same color - these are 2 inches wide. The bottom stay, which is a long bracket with the form of the letter "Z", only not as steep, has two holes, one that goes into the BB and one that goes into the chainguard. This is the lowest contact point of the chainguard. This bracket is 1-1/8 inches wide. -- underground experts united http://user.it.uu.se/~embe8573 |
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