Good & easy way to add a seatpost clamp to a frame without one?? (quill style post)
05-07-21, 10:03 AM
#26
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Adding a binder bolt
I have a 1985? Puegeot Triathlon made with Vitus 980 that uses a quill seat post. I am considering the above modification. The front mounted clamp that Nate does is not new I saw it on a bikes in the late 70's a except there was no horizontal slots just a vertical slot with stress releif holes top and bottom. There isn't alot of clamping movement in the mid tube clamp design. The seatpost has to fit correctly (snug) for this to work. to reduce the tube diameter by 0.1mm you need to reduce the cicumfrence by PI . So you will see 0.31 mm of slot narrowing for each 0.1mm of seat tube diameter reduction.
My bike also came with a 26.4 seat post that is a sloppy fit. I measured the seat tube ID at 26.9mm with a cheap caliper. I thnk the correct size seatpost is 26.6 or 26.8mm. It is not 26.4. i will need to do test fits amd determine the best fit before i start. The top of my seat tube and lug was oval because of the original undersized seat post. I rounded the seat tube/lug by gently expanding the quill at the top of the seat tube which seemed to work well.
My bike also came with a 26.4 seat post that is a sloppy fit. I measured the seat tube ID at 26.9mm with a cheap caliper. I thnk the correct size seatpost is 26.6 or 26.8mm. It is not 26.4. i will need to do test fits amd determine the best fit before i start. The top of my seat tube and lug was oval because of the original undersized seat post. I rounded the seat tube/lug by gently expanding the quill at the top of the seat tube which seemed to work well.
04-18-22, 05:32 PM
#27
Peugeot PSV10 or somethin
Thread Starter
Sorry, I forgot to post back. I got a reply from the frame builder of the orange frame. He said the tubing with those builds was really thick, and he didn't advise cutting up my frame, so I didn't. I'm glad I didn't do it! What I ended up doing was using a 26.6 which was a much more snug fit, but not too tight, and a very long steel post, and it clamps up fine without cutting a slot at all. probably introducing some more stress and potential points of failure by doing this, but with the steel post I'm not so worried. This shaft collar clamp is also chamfered on the edges. Sorry I don't have better pics.
What did you end up doing Lars? If your project has been on the backburner, I hope my post helps 
I have a 1985? Puegeot Triathlon made with Vitus 980 that uses a quill seat post. I am considering the above modification. The front mounted clamp that Nate does is not new I saw it on a bikes in the late 70's a except there was no horizontal slots just a vertical slot with stress releif holes top and bottom. There isn't alot of clamping movement in the mid tube clamp design. The seatpost has to fit correctly (snug) for this to work. to reduce the tube diameter by 0.1mm you need to reduce the cicumfrence by PI . So you will see 0.31 mm of slot narrowing for each 0.1mm of seat tube diameter reduction.
My bike also came with a 26.4 seat post that is a sloppy fit. I measured the seat tube ID at 26.9mm with a cheap caliper. I thnk the correct size seatpost is 26.6 or 26.8mm. It is not 26.4. i will need to do test fits amd determine the best fit before i start. The top of my seat tube and lug was oval because of the original undersized seat post. I rounded the seat tube/lug by gently expanding the quill at the top of the seat tube which seemed to work well.
My bike also came with a 26.4 seat post that is a sloppy fit. I measured the seat tube ID at 26.9mm with a cheap caliper. I thnk the correct size seatpost is 26.6 or 26.8mm. It is not 26.4. i will need to do test fits amd determine the best fit before i start. The top of my seat tube and lug was oval because of the original undersized seat post. I rounded the seat tube/lug by gently expanding the quill at the top of the seat tube which seemed to work well.
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04-18-22, 05:35 PM
#28
Peugeot PSV10 or somethin
Thread Starter
I also want to mention I don't actually understand how it clamps up OK like this, I am using normal grease I think, and it's really not too snug - seems about right. Any metallurgist/frame builder want to comment on how this is working and how it affects the steel?
