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  1. #1
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    Not shure where to ask this but...

    Do you think is possible to machine down a 30.9mm adjustable seatpost down to 30mm?

    I just saw a 30.9 mm Joplin adjustable seatpost in ebay, and wondered if it would be possible to machine it down to 30 mm, so they will fit mi old Kona Coiler.

    How thick the seatpost walls are? I think removing 0.45mm all around wouldn't compromise any strenght...

  2. #2
    Moose Member
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    I'm not shure if it will compromise strength, but I'm pretty shure it's spelled "sure" not "shure..."

    I personally wouldn't machine down any bike part, but I have been known to break stuff a lot. If you think you can do it, go for it.

  3. #3
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    My short answer would be no.

    Im sure it could be done by someone, but machinist aren't exactly cheap ($80+ hr) and depending on the wall thickness of the seatpost I dont think machining off .45mm would leave much left. A shop would certainly charge a minum rate of an hour to include setup time and such.

    .45mm doesnt sound like much, but if the wall dia. is 1mm for example machining away .45mm would compromise nearly 50% of the thickness and I shouldn't have to explain further what that would do to the strength and durability of the seatpost.

    Best to pass on that post and get one that will fit properly ...or buy it and save it for a different bike build.

  4. #4
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    I live in Mexico, here a machinist would charge about 20 bucks to do it, The thing is, I don't know how thick the seatpost walls are, but I think the internals in the 30.9 and 31.6 seatposts are the same. The point is, maybe only the outer tube of the 30.9 has an already reduced diameter to fit this measure, It wouldn't hurt to remove a little more (0.45 m is like nothing) and see what happens, haha.

    Or, I can buy the seatpost, measure the outer tube OD and ID, and see if it's feasible.

  5. #5
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    Would it be possible to ream the inside of the seat tube? An adjustable reamer should be able to do it. One problem could be the longitudinal slot on the seat tube to clamp the seatpost. One could use a small file to bevel the inside edge of the slot so the reamer's teeth don't hit it and break.

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