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#21
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Quill seat posts for MTB?
On Sun, 4 Dec 2016 20:32:32 -0500, Frank Krygowski
wrote: On 12/4/2016 7:12 PM, John B. wrote: On Sun, 04 Dec 2016 08:11:18 -0800, Joerg wrote: On 2016-12-02 16:38, John B. wrote: On Fri, 02 Dec 2016 09:38:30 -0800, Joerg wrote: Folks, In the old days they were available but can't find modern ones for MTB. https://www.youtube.com/watch?v=5EkigpkVXLY Fixing a seat post only at the top (kind of) works for regular bikes that aren't used on harsh turf but not for MTB with heavy loads. Mine started creaking to no end and that's probably not good for the frame. So I am looking for a longer seat post but ideally with quill. Any hints who still carries that? Why is clamping the seat post with a clamp at the top actually different from clamping the seat post at the bottom? It needs to be clamped at the top _and_ the bottom. If you clamp it only in one place there will always be an ever so slight rocking. This produces creaking, wear and most annoyingly a gradual sagging. Theoretically at least the seat post is supposed to be sliding fit in the seat tube with minimal play so clamping at one end is very much the same as clamping at the other. "Minimal" is the key word here. It cannot be zero and even if it was it would wear with use. A minimal gap is required in order to get the seat post in and out and also because of the usual factory tolerances. This causes minimal rocking back and forth. A quill at the bottom in addition to the usual clamp at the top will avoid that. Not a new concept, I had that on an old bike. Aside from the creaking, no matter how hard I adjusted the top clamp the only way I could prevent a gradual sag when riding a lot of washboard turf was to smear toothpaste around the top of the post where it clamps. Not the gel type for electric brushing but the regular stuff with some grit in there. Coincidentally that's also how I prevented the MTB stem from coming loose without exceeding the 5Nm torque limit. As you mention a friend who is a machinist I suggest that the only problem with making a seat post is how to tighten the bottom clamp. A through bolt running from the top of the post to the clamp nut at the bottom is certainly doable just as the old 1 inch quill stems. Added to a conventional "top clamp" that should hold the seat post even if an elephant should sit on it. The problem comes about because the seat covers the top of the seat post and makes tightening the quill bold difficult but given that once the "correct" seat position is determined one doesn't usually re-adjust he seat frequently it should be easy enough. Just install the seat using the normal clamp and adjust to fit. Then remove the seat, tighten the quill bolt and reinstall the seat. Sounds workable to me. You know, there is another solution. Simply drill a series of holes in the seat post, say 1/2" apart. A hole through the seat tube and Bob's your uncle. Use a 1/4" grade 8 bolt, maybe 735 pounds tensile strength, probably in the neighborhood of 440 pounds sheer strength. If one used a "spring cotter" rather than a nut it could even be field adjustable without tools. -- cheers, John B. |
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#22
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Quill seat posts for MTB?
Bolt no good...no surface area (s)
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#23
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Quill seat posts for MTB?
On 2016-12-04 22:39, John B. wrote:
On Sun, 4 Dec 2016 20:32:32 -0500, Frank Krygowski wrote: On 12/4/2016 7:12 PM, John B. wrote: On Sun, 04 Dec 2016 08:11:18 -0800, Joerg wrote: On 2016-12-02 16:38, John B. wrote: On Fri, 02 Dec 2016 09:38:30 -0800, Joerg wrote: Folks, In the old days they were available but can't find modern ones for MTB. https://www.youtube.com/watch?v=5EkigpkVXLY Fixing a seat post only at the top (kind of) works for regular bikes that aren't used on harsh turf but not for MTB with heavy loads. Mine started creaking to no end and that's probably not good for the frame. So I am looking for a longer seat post but ideally with quill. Any hints who still carries that? Why is clamping the seat post with a clamp at the top actually different from clamping the seat post at the bottom? It needs to be clamped at the top _and_ the bottom. If you clamp it only in one place there will always be an ever so slight rocking. This produces creaking, wear and most annoyingly a gradual sagging. Theoretically at least the seat post is supposed to be sliding fit in the seat tube with minimal play so clamping at one end is very much the same as clamping at the other. "Minimal" is the key word here. It cannot be zero and even if it was it would wear with use. A minimal gap is required in order to get the seat post in and out and also because of the usual factory tolerances. This causes minimal rocking back and forth. A quill at the bottom in addition to the usual clamp at the top will avoid that. Not a new concept, I had that on an old bike. Aside from the creaking, no matter how hard I adjusted the top clamp the only way I could prevent a gradual sag when riding a lot of washboard turf was to smear toothpaste around the top of the post where it clamps. Not the gel type for electric brushing but the regular stuff with some grit in there. Coincidentally that's also how I prevented the MTB stem from coming loose without exceeding the 5Nm torque limit. As you mention a friend who is a machinist I suggest that the only problem with making a seat post is how to tighten the bottom clamp. A through bolt running from the top of the post to the clamp nut at the bottom is certainly doable just as the old 1 inch quill stems. Added to a conventional "top clamp" that should hold the seat post even if an elephant should sit on it. That is exactly what I was planning to do if I can't find an off-the-shelf quill post. The problem comes about because the seat covers the top of the seat post and makes tightening the quill bold difficult but given that once the "correct" seat position is determined one doesn't usually re-adjust he seat frequently it should be easy enough. Just install the seat using the normal clamp and adjust to fit. Then remove the seat, tighten the quill bolt and reinstall the seat. Sounds workable to me. I'll see if there would be a spot in the top plate that can be drilled without compromising its integrity. The cone that spreads apart the newly slit section of the post bottom does not need much force if shallow-angled and greased. So a 4mm or similar all-thread should suffice. The MTB is only ridden by me and due to electrical wiring and such the seat height can't easily be adjusted anyhow. So I'd just mount it like usual, mark the post and then do the mods. That way the all-thread pulling in the cone can be tightened and shortened while the seat is off. If can still be adjusted up and down a bit but the seat would always have to come off in order to access the tightening nut on the all-thread. You know, there is another solution. Simply drill a series of holes in the seat post, say 1/2" apart. A hole through the seat tube and Bob's your uncle. Use a 1/4" grade 8 bolt, maybe 735 pounds tensile strength, probably in the neighborhood of 440 pounds sheer strength. I am not going to drill the frame :-) Voids the warranty and who knows what else it could do. If one used a "spring cotter" rather than a nut it could even be field adjustable without tools. A spring latch like on walkers or market umbrellas would prevent the post from sliding down but not from rocking. Rocking is the key problem I have, resulting in nasty creaking and probably wear in the frame. -- Regards, Joerg http://www.analogconsultants.com/ |
#24
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Quill seat posts for MTB?
On Saturday, December 3, 2016 at 12:30:15 AM UTC-8, John B. wrote:
On Fri, 2 Dec 2016 19:09:33 -0800 (PST), Doug Landau Why is clamping the seat post with a clamp at the top actually different from clamping the seat post at the bottom? Theoretically at least the seat post is supposed to be sliding fit in the seat tube with minimal play so clamping at one end is very much the same as clamping at the other. - Because if clamped at the top, the pinch bolt will be under tension, and able to absorb the tension put on it by the post, before the welds can experience it. Google brandt+pretension Certainly the pinch bolt is tightened. But is the pinch bolt, in some manner independent of all else? Just floating there in space absorbing all stresses and strains imposed on it? Or is it simply a clamp that transfers loads imposed on it to the bicycle frame. Is the fact that all seat posts have some minimum insertion limits important? Given that the seat clamp tension bolt "absorbs the tension"? The minimum insertion limit is so that the seatpost doesn't come busting thru the seat tube at its (the seatpost's) bottom edge, not having enough leverage, when pivoting where it exits the seattube, when lateral load is applied at the top of the post. Remove the pinch bolt, push sideways on the seat, or even forward or back, and the ears that the pinch bolt goes thru will be spread a little bit, right? In other words, the post is trying to make the opening at the top of the seattube an oval, by placing tension on the walls, at the opening, from the inside, right? I suggest that if tight, the pinch bolt will absorb this tension, which then cannot be experienced by the tube itself, until it exceeds the tension in the pinch bolt. The pinch bolt simply compresses the seat tube to clamp the seat post in place and resists further distortion to some extent but force applied to the seat post is absorbed by the seat tube. Can't be any other way. The pinch bolt, once under tension, will prevent whatever it is compressing from experiencing tension from being pushed from the inside. In this case, the lip and upper end of the seat tube. Can't be any other way. You are not understanding. https://www.google.com/webhp?sourcei...nsioned+steel+ |
#25
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Quill seat posts for MTB?
due to electrical wiring ? the bike or yours ? use the sand stupid
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#26
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Quill seat posts for MTB?
On Sunday, December 4, 2016 at 10:39:53 PM UTC-8, John B. wrote:
On Sun, 4 Dec 2016 20:32:32 -0500, Frank Krygowski wrote: On 12/4/2016 7:12 PM, John B. wrote: On Sun, 04 Dec 2016 08:11:18 -0800, Joerg wrote: On 2016-12-02 16:38, John B. wrote: On Fri, 02 Dec 2016 09:38:30 -0800, Joerg wrote: Folks, In the old days they were available but can't find modern ones for MTB. https://www.youtube.com/watch?v=5EkigpkVXLY Fixing a seat post only at the top (kind of) works for regular bikes that aren't used on harsh turf but not for MTB with heavy loads. Mine started creaking to no end and that's probably not good for the frame. So I am looking for a longer seat post but ideally with quill. Any hints who still carries that? Why is clamping the seat post with a clamp at the top actually different from clamping the seat post at the bottom? It needs to be clamped at the top _and_ the bottom. If you clamp it only in one place there will always be an ever so slight rocking. This produces creaking, wear and most annoyingly a gradual sagging. Theoretically at least the seat post is supposed to be sliding fit in the seat tube with minimal play so clamping at one end is very much the same as clamping at the other. "Minimal" is the key word here. It cannot be zero and even if it was it would wear with use. A minimal gap is required in order to get the seat post in and out and also because of the usual factory tolerances. This causes minimal rocking back and forth. A quill at the bottom in addition to the usual clamp at the top will avoid that. Not a new concept, I had that on an old bike. Aside from the creaking, no matter how hard I adjusted the top clamp the only way I could prevent a gradual sag when riding a lot of washboard turf was to smear toothpaste around the top of the post where it clamps. Not the gel type for electric brushing but the regular stuff with some grit in there. Coincidentally that's also how I prevented the MTB stem from coming loose without exceeding the 5Nm torque limit. As you mention a friend who is a machinist I suggest that the only problem with making a seat post is how to tighten the bottom clamp. A through bolt running from the top of the post to the clamp nut at the bottom is certainly doable just as the old 1 inch quill stems. Added to a conventional "top clamp" that should hold the seat post even if an elephant should sit on it. The problem comes about because the seat covers the top of the seat post and makes tightening the quill bold difficult but given that once the "correct" seat position is determined one doesn't usually re-adjust he seat frequently it should be easy enough. Just install the seat using the normal clamp and adjust to fit. Then remove the seat, tighten the quill bolt and reinstall the seat. Sounds workable to me. You know, there is another solution. Simply drill a series of holes in the seat post, say 1/2" apart. A hole through the seat tube and Bob's your uncle. Use a 1/4" grade 8 bolt, maybe 735 pounds tensile strength, probably in the neighborhood of 440 pounds sheer strength. If it bears weight (your pin), it'll ovalize the holes in the seat tube, and be loose and rattle. It will bear weight because, as Gene pointed out, its flat head can't hold against the round tube. |
#27
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Quill seat posts for MTB?
On Sunday, December 4, 2016 at 10:39:53 PM UTC-8, John B. wrote:
On Sun, 4 Dec 2016 20:32:32 -0500, Frank Krygowski wrote: On 12/4/2016 7:12 PM, John B. wrote: On Sun, 04 Dec 2016 08:11:18 -0800, Joerg wrote: On 2016-12-02 16:38, John B. wrote: On Fri, 02 Dec 2016 09:38:30 -0800, Joerg wrote: Folks, In the old days they were available but can't find modern ones for MTB. https://www.youtube.com/watch?v=5EkigpkVXLY Fixing a seat post only at the top (kind of) works for regular bikes that aren't used on harsh turf but not for MTB with heavy loads. Mine started creaking to no end and that's probably not good for the frame. So I am looking for a longer seat post but ideally with quill. Any hints who still carries that? Why is clamping the seat post with a clamp at the top actually different from clamping the seat post at the bottom? It needs to be clamped at the top _and_ the bottom. If you clamp it only in one place there will always be an ever so slight rocking. This produces creaking, wear and most annoyingly a gradual sagging. Theoretically at least the seat post is supposed to be sliding fit in the seat tube with minimal play so clamping at one end is very much the same as clamping at the other. "Minimal" is the key word here. It cannot be zero and even if it was it would wear with use. A minimal gap is required in order to get the seat post in and out and also because of the usual factory tolerances. This causes minimal rocking back and forth. A quill at the bottom in addition to the usual clamp at the top will avoid that. Not a new concept, I had that on an old bike. Aside from the creaking, no matter how hard I adjusted the top clamp the only way I could prevent a gradual sag when riding a lot of washboard turf was to smear toothpaste around the top of the post where it clamps. Not the gel type for electric brushing but the regular stuff with some grit in there. Coincidentally that's also how I prevented the MTB stem from coming loose without exceeding the 5Nm torque limit. As you mention a friend who is a machinist I suggest that the only problem with making a seat post is how to tighten the bottom clamp. A through bolt running from the top of the post to the clamp nut at the bottom is certainly doable just as the old 1 inch quill stems. Added to a conventional "top clamp" that should hold the seat post even if an elephant should sit on it. The problem comes about because the seat covers the top of the seat post and makes tightening the quill bold difficult but given that once the "correct" seat position is determined one doesn't usually re-adjust he seat frequently it should be easy enough. Just install the seat using the normal clamp and adjust to fit. Then remove the seat, tighten the quill bolt and reinstall the seat. Sounds workable to me. You know, there is another solution. Simply drill a series of holes in the seat post, say 1/2" apart. A hole through the seat tube and Bob's your uncle. Use a 1/4" grade 8 bolt, maybe 735 pounds tensile strength, probably in the neighborhood of 440 pounds sheer strength. If one used a "spring cotter" rather than a nut it could even be field adjustable without tools. -- cheers, John B. 1/4" ?!? Way overkill. The shear strength of a #6 screw is 1500 Lbs |
#28
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Quill seat posts for MTB?
WELL, I have seen this bolt in post n the bolt bends, the hole ovals...no bearing surface area. 'Like' the post comes loose so....? where's one on the floor off the rack.... hole bolt post ?
Now here's a wannabe mountain ear who goes on abt hammering pins with rocks but a dollop of sand into the post lube ? |
#29
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Quill seat posts for MTB?
1/4" ?!? Way overkill. The shear strength of a #6 screw is 1500 Lbs
a .25 inch bolt in grade 5 is not taking 1500 pounds the way ura gonna use it in the field. I doahn have the equation for this but that bolt under 75 pounds over 10 miles/700 miles will fail. more surface area. gotta replace bolt. the old saw is a 6 legged sofa under 4 fat women...calculate pressure under sofa feet vs shinylvinyl/carpet or hardwood flooring. |
#30
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Quill seat posts for MTB?
On Mon, 05 Dec 2016 07:29:09 -0800, Joerg
wrote: On 2016-12-04 22:39, John B. wrote: On Sun, 4 Dec 2016 20:32:32 -0500, Frank Krygowski wrote: On 12/4/2016 7:12 PM, John B. wrote: On Sun, 04 Dec 2016 08:11:18 -0800, Joerg wrote: On 2016-12-02 16:38, John B. wrote: On Fri, 02 Dec 2016 09:38:30 -0800, Joerg wrote: Folks, In the old days they were available but can't find modern ones for MTB. https://www.youtube.com/watch?v=5EkigpkVXLY Fixing a seat post only at the top (kind of) works for regular bikes that aren't used on harsh turf but not for MTB with heavy loads. Mine started creaking to no end and that's probably not good for the frame. So I am looking for a longer seat post but ideally with quill. Any hints who still carries that? Why is clamping the seat post with a clamp at the top actually different from clamping the seat post at the bottom? It needs to be clamped at the top _and_ the bottom. If you clamp it only in one place there will always be an ever so slight rocking. This produces creaking, wear and most annoyingly a gradual sagging. Theoretically at least the seat post is supposed to be sliding fit in the seat tube with minimal play so clamping at one end is very much the same as clamping at the other. "Minimal" is the key word here. It cannot be zero and even if it was it would wear with use. A minimal gap is required in order to get the seat post in and out and also because of the usual factory tolerances. This causes minimal rocking back and forth. A quill at the bottom in addition to the usual clamp at the top will avoid that. Not a new concept, I had that on an old bike. Aside from the creaking, no matter how hard I adjusted the top clamp the only way I could prevent a gradual sag when riding a lot of washboard turf was to smear toothpaste around the top of the post where it clamps. Not the gel type for electric brushing but the regular stuff with some grit in there. Coincidentally that's also how I prevented the MTB stem from coming loose without exceeding the 5Nm torque limit. As you mention a friend who is a machinist I suggest that the only problem with making a seat post is how to tighten the bottom clamp. A through bolt running from the top of the post to the clamp nut at the bottom is certainly doable just as the old 1 inch quill stems. Added to a conventional "top clamp" that should hold the seat post even if an elephant should sit on it. That is exactly what I was planning to do if I can't find an off-the-shelf quill post. The problem comes about because the seat covers the top of the seat post and makes tightening the quill bold difficult but given that once the "correct" seat position is determined one doesn't usually re-adjust he seat frequently it should be easy enough. Just install the seat using the normal clamp and adjust to fit. Then remove the seat, tighten the quill bolt and reinstall the seat. Sounds workable to me. I'll see if there would be a spot in the top plate that can be drilled without compromising its integrity. The cone that spreads apart the newly slit section of the post bottom does not need much force if shallow-angled and greased. So a 4mm or similar all-thread should suffice. I would really suggest something larger. Most quill" stems use about a 6 mm bolt so perhaps there is a reason :-) Another point, you seem to be talking about a hollow seat post, split, with a cone shaped wedge to spread the bottom of the post. This is going to take a hammer to drive out if you ever try to move the seat post and I doubt that a 4mm bolt the length of the seat post is going to suffice. The MTB is only ridden by me and due to electrical wiring and such the seat height can't easily be adjusted anyhow. So I'd just mount it like usual, mark the post and then do the mods. That way the all-thread pulling in the cone can be tightened and shortened while the seat is off. If can still be adjusted up and down a bit but the seat would always have to come off in order to access the tightening nut on the all-thread. You know, there is another solution. Simply drill a series of holes in the seat post, say 1/2" apart. A hole through the seat tube and Bob's your uncle. Use a 1/4" grade 8 bolt, maybe 735 pounds tensile strength, probably in the neighborhood of 440 pounds sheer strength. I am not going to drill the frame :-) Voids the warranty and who knows what else it could do. If one used a "spring cotter" rather than a nut it could even be field adjustable without tools. A spring latch like on walkers or market umbrellas would prevent the post from sliding down but not from rocking. Rocking is the key problem I have, resulting in nasty creaking and probably wear in the frame. -- cheers, John B. |
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