Bent seat tubes, draw style bender, tube roller, or pre bent?- Mtbr.com
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  1. #1
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    Bent seat tubes, draw style bender, tube roller, or pre bent?

    I need to do some bent seat tube bikes (i.e. short stays and 29er+).

    In any case, I have a Pro Tools 105 bender but don't yet have a die for 1.25" tubes.

    Thinking through my options....

    Option #1 -- Pro tools 105 bender and a custom 7" CLR die so I can bend 0.049 wall straight gauge (or may push things and do 0.035 wall). Anyone doing this?

    Option #2 -- Tube roller (need to buy one). Still thinking about which one to get.

    Option #3 -- Pre bent tubes; are there any available?

    What are your thoughts? What are you using and how is it working?

  2. #2
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    Mark,

    I can see this thread expanding as it is very topical.

    I will offer my experiences of option 3, Pre-bent.

    Nova supply a Pre-bent Down tube in 35mm, with a 15* bend. It is 9/6/9, and the butt tapers through the bend and exits at .6mm. I fit a reducer that I have made up. The Seat post size can be made up to any size as it is a custom made fitted reducer. I have used it right down to 385mm chain stay. The 35mm gives a very solid feel to the frame - no sway in the pedal stroke. Only use in hard-tail designs, as I feel .6mm is too light for suspension attachment stresses.

    Eric
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    If I don't make an attempt, how will I know if it will work?

  3. #3
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    Quote Originally Posted by Eric Malcolm View Post
    Only use in hard-tail designs, as I feel .6mm is too light for suspension attachment stresses.
    My primary personal focus is hardtail 29ers and soon to be 29+. With the stuff that I ride and the market that I really want to serve I think .6mm is too light. I wish there were some good seat tube specific options with nice bends.

    With enough interest from others we might be able to convince True Temper, Reynolds, or NOVA to create good tubes with 9/6/1.0 butting. Really on the seat cluster of a 29er that sees serious trail I would like to have a thick butt.

    With the lack of pre-bent tubes I am thinking about a tube roller or getting a 7" CLR die made up for my Pro Tools 105 bender. Part of me feels like the 7" CLR die would produce better bend shape although Pro Tools tells me they don't feel like it could handle 0.035" wall tubing. It should be possible to do the bend with 0.049" wall tubing and using a 1.25" diameter tube where it is segmented with 0.049" at the bend and 0.035" with the upper part plus a nice thick top section for the seat tube should provide robust strength without too much weight.

    The advantage for the tube roller is that it would facilitate making a slightly lighter frame because I could use 0.035" wall tubing and roll a bend that would have a very large effective CLR to avoid the potential for tube damage in the bending process. My concern is that in small size 29ers it may be hard to have a straight section that is long enough for good seat post insertion for dropper posts.

    There is a lot to consider; it could be that I will eventually end up with a tube roller but in the near term I am leaning towards getting the custom 7" CLR die made up for my existing bender. I think the quote was something like $400 for the custom die.

  4. #4
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    The Nova 35mm DT with Paragon's 30.9 sleeve seems like a pretty great option. Haven't tried it myself, but Carl Strong is down the road from me and he's been doing it. If it's good enough for him... Still doesn't give you a ton of extra clearance though.

    I'm making a form bender for 35mm ST's that will go in a 12 ton press. I'm in school and have free CNC usage so that makes it more there.

    I haven't heard great things about the pro tools bender. I've used my roller on the last several bikes, but I have to weld on an extension to roll it and I just don't think that's worth it.

    Also are you sure you want to invest in 1.25 dies? if you're building MTB's why not a 1.375, opens up a lot more dropper post options and dropper posts are the bomb.

  5. #5
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    Quote Originally Posted by adarn View Post
    Also are you sure you want to invest in 1.25 dies? if you're building MTB's why not a 1.375, opens up a lot more dropper post options and dropper posts are the bomb.
    I will eventually do both styles but wanted to start with bikes built around 27.2mm posts.

    I like the 1.25" and 1.375" formats as options. I figure that I would do the smaller seat tube style bikes first and then later do the larger seat tube style. The 1.25" format saves a little bit of weight on the bikes so unless someone really wants the internal or already has a dropper I think 27.2mm posts make sense.

  6. #6
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    Making curved seat tubes is easy with any number of techniques. I'd just get the HF roller and some Swag dies if I were you. Cheap, reliable, and can be used for other projects. Not great for super small radius/tight bends, though.

    -Walt

  7. #7
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    There are no cheap options for tube rollers in the UK, so I currently use a plywood former to match a 29er wheel radius (laminated then cut a semi-circular profile around the circumference using a holesaw). Use an aluminium slipper with a ballrace running along the back. It is OK ish - still tends to leave a few small ripples in the back of the tube. I'm using household plumbing compression fittings to keep the tube filled with sand.

    It needs a massive amount of force with just basic cro-mo tubing - I usually put an even bigger bar in the lever where my kid is having a go - and no, he didn't manage to bend it :-) Second photo shows where we managed to kink it by trying a bend too far....

    Bent seat tubes, draw style bender, tube roller, or pre bent?-p1020591.jpg

    Bent seat tubes, draw style bender, tube roller, or pre bent?-p1020594.jpg

  8. #8
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    Long time lurker- newbie builder alert

    I work in a shop, and I was told a while back that one trick to bending without deformations is to fill the tube with sand. The idea makes sense, it will help keep its original diameter because there is something inside the tube. Never tried it through . . .

  9. #9
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    I've never found the sand makes a big difference bending cold. I'm using fine kiln dried sand, but the real stuff if you can get it is foundry / green sand.

    The (now retired) coppersmith at work once bent me a shower curtain rail out of 1" stainless tube. That was packed with foundry sand and hot bent freehand through a lovely big sweeping curve. But cooking tubes like that isn't much use for bikes....

  10. #10
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    Search 44bikes instagram he set up a bending back in December for seat tubes.

  11. #11
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    Walt sells bent single-butted STs for 27.2 seatposts
    I was surprised he didn't mention it above

  12. #12
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    FYI, Mick - you will have better luck with larger radius. There is actually no need to match the radius of the wheel unless you are doing something really, really weird. A much larger radius bend (even over a very short distance) is plenty for tire clearance purposes even on super short stay frames.

    And FYI, yes, I do sell curved tubes in most common sizes for a variety of purposes. I prefer not to discuss that here, though, to avoid any appearance of impropriety - if you are curious, shoot me an email.

    -Walt

  13. #13
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    Protip: do 2 at once.

    -Walt

    Quote Originally Posted by adarn View Post
    I've used my roller on the last several bikes, but I have to weld on an extension to roll it and I just don't think that's worth it.

  14. #14
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    Quote Originally Posted by Walt View Post
    Protip: do 2 at once.

    -Walt
    ...How did I not think of that! my life is changed. Haha. Thanks Walt.

  15. #15
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    What about the 28.6 pre-bent Columbus tube?

  16. #16
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    When you are old enough to buy beer I will collect for all my "help".

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    Quote Originally Posted by adarn View Post
    ...How did I not think of that! my life is changed. Haha. Thanks Walt.

  17. #17
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    Quote Originally Posted by Walt View Post
    When you are old enough to buy beer I will collect for all my "help".

    -Walt
    Hey! I'm old enough to do that... But maybe I shouldn't tell you that... I owe you lots of help.

  18. #18
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    Thanks for the advice Walt. A tube roller is on my list of nice things to get one day....

    Hello Mr Shand

    I didn't know there was a pre-bent Columbus tube - presumably you get it from Ceeway? Do you know what the part number is? Is it plain gauge cro-mo (Gara etc, which is all I've been using) or something fancier?

  19. #19
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    Quote Originally Posted by mickuk View Post
    I didn't know there was a pre-bent Columbus tube - presumably you get it from Ceeway? Do you know what the part number is? Is it plain gauge cro-mo (Gara etc, which is all I've been using) or something fancier?
    It's ZON113550110F.

    28.6 and externally butted for 27.2 post, 0.8/0/6/1.2 550L, Zona material.

    It's a nice smooth bend too :

    Bent seat tubes, draw style bender, tube roller, or pre bent?-bent_seattube.jpg

    Don't know if Peter carries it or not. Assuming he can get it if he doesn't.

    Steven

  20. #20
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    Sweet! Saving that for later use...

  21. #21
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    Quote Originally Posted by shandcycles View Post
    It's ZON113550110F.

    28.6 and externally butted for 27.2 post, 0.8/0/6/1.2 550L, Zona material.

    It's a nice smooth bend too :

    Click image for larger version. 

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    Don't know if Peter carries it or not. Assuming he can get it if he doesn't.

    Steven
    This looks good. The Zona tube it is based on (external butt) has a nice long butt length off the BB end of 245 x .8mm, this would make it good for most non-drop seat post applications. Columbus also make a larger Dia seat tube that they need to consider bending as well for the dropper crowd.

    Eric
    If I don't make an attempt, how will I know if it will work?

  22. #22
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    I'm thinking more along the lines of tucking the rear wheel in for TT builds (I'm not so much a MTB guy).

  23. #23
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    Quote Originally Posted by Eric Malcolm View Post
    Columbus also make a larger Dia seat tube that they need to consider bending as well for the dropper crowd.
    This.^^ (and they know it)

  24. #24
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    Is there anyone in US selling this Columbus bent st?

  25. #25
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    I do 2 nova ex-butt seat tubes welded together in a HF roller with Swag dies.
    Usually just do sand, but when I worry about a really tight bend, or when the first 2 tried have crinkled, then I've had good success with Resin WS8. It's a non-toxic cerrabend like wax, melts at 150 deg F, so I can use my wife's oven when she's out shopping Aluminum foil in a pan usually leaves no trace. It's from the UK.Bent seat tubes, draw style bender, tube roller, or pre bent?-14360504597_915b90df61_c.jpg
    Big help on fat seat stays.
    I have several benders but the rollers work well for seat tubes.
    andy walker
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