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  1. #1
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    El Rebeco - short ass 29er hardtail

    Hi guys.
    This is my first real MTB project. The last one was some kind of monstercross / full rigid dropbar 29er hybrid whatever - which made me fall in love with offroad cycling.

    I love my Monstercross bike, but I want something to ride more relaxed when it comes to technical and descending terrain.

    This is the geometry (some kind of allmountain or whatever, I guess)




    Itīs designed for a tapered Epicon (15mm through axle), setup with 5" travel. The rear will get the 2SoulsCycles X12 dropouts.

    Because these are my first X12 dropouts, I decided to build a chainstay-mitering jig.
    Welded the dropouts to the chainstays (bent from round 4130 tubing 19x0.9mm = 3/4"x0.035)




    Put them in the jig and let the mill do the job.


    Worked out well (Iīll add a cross-bracing after the seattube is welded)




    This is a Conti Mountain King 29x2.4


    Then I made myself a rollbender with 31.8mm dies.



    curved seattube from 31.8x0.9mm = 1.25x0.035 straight gauge 4130. The radius is smaller than the rearwheel to get a long straight section at the end - so I can run (and drop when needed) a rigid seatpost. Just in case I donīt like the dropper-post I just ordered.


    Thatīs it so far. Next steps will be mitering the main-triangle.

    Cheers, Michael
    Last edited by MiWi; 08-18-2013 at 11:51 PM.

  2. #2
    pvd
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    Great job on the prints. It shows that you really get it, at least on paper. #2 is supurbe other than referencing drop instead of bb height.

    You may be digging a hole with the bent tube. It's really not that important to have 'super duper' short stays on a bike. It's nice, but the bent seat tube creates far more major problems. Since your print doesn't show the bent tube, you won't be getting the seat into the right position. You should update the prints to check.

    I don't like bent seat tubes as they don't allow for quality fine adjustement of saddle height without really screwing up riding position. You have to nail it or it sucks.

    Your detail and craftsmanship look great.

  3. #3
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    Thanks for your reply Peter.

    I didnīt go for super short. 425 was the way my wheight distribution might be well o.k. Would have been enough space to go for 415mm or something like that but didnīt want that. To short for a 191cm guy imho.

    Concerning the seattube angle (the effective (!) seattube angle).
    The first 2 sketches only show the geometry for the jig / for straight tubes.
    RattleCAD canīt do curved tubes. That is way I implement my curved tubes via CAD. See the green line for effective angle as shown in the sketches.

    El Rebeco - short ass 29er hardtail-effseattubeangle.jpg
    (this sketch shows 120mm sag / end of travel to also check the space between frontwheel and downtube)

    Made a Dummy-Seatpost / Seattube extension to the length of my exact seat-position.
    The jig-cone connected the seattube/the dummy where my saddle will be. So the jig is setup to the effective seattube angle.
    In this picture you can see that my jig got an extra long rail for the seattube. This way a can grab/hold a seattube far up high, where my sattle will be lateron.


    The longitudinal shift of the saddle-position when lowering is no issue for me. I got a fix riding position which is fixed in a range of +- 2mm on all of my bikes.
    I donīt care for the dropped position when descending. Itīs even better that the saddle moves more forward because of the curved seattube. This way it is easyer to work my center of gravity behind the saddle / where I need it.

  4. #4
    Randomhead
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    is that a homemade radius toolpost I see? Any more pictures of it?

  5. #5
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    Yes its homemade. (All my tools are homemade.)
    I have 2 radius tools. For large radius and for small radius / immersion.
    I can make another picture of the immersion radius tool used for the roller dies this evening.
    This is the other one / big one, the small one is quite the same but with a continious shaft.


    Itīs simply just a stainless steel rod running in tight bronze bushings.
    Both use 8mm HSS cutting steels or old 8mm drill ground to a "turning tool".

  6. #6
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    Made a better picture of the radius turning tool.
    El Rebeco - short ass 29er hardtail-cimg8319.jpg

  7. #7
    Randomhead
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    I love it, thanks for the pics.

  8. #8
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    Most important: The handhold is carbon and the clamp is titan. Everything else doesnīt work.

    (in fact those are relics from when my father broke his pelvis and most of his leg-bones in a motorcycle crash)

  9. #9
    pvd
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    Very good work. It's nice to see so much quality thought going into the bike well before metal starts getting cut. Looking forward to seeing more.

  10. #10
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    Interesting, eh?

    As I learned, and as it occurred to me somewhere early in that journey, it was the process itself that consumed most of the energy and creativity. The bike itself was almost a fait accompli.

    Quite creative and accomplished you are, Sir. Obviously, possessing a lot of parallel/tangential knowledge. The bike will be marvelous, no doubt!
    Most people ply the Well Trodden Path. A few seek a different way, and leave a Trail behind.
    - John Hajny, a.k.a. TrailMaker

  11. #11
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    Pretty amazing stuff so far.

    Personally, with stays that short, I'd prefer a slacker head angle (~68), but that is me, not you. Looking forward to seeing the completed bike!

  12. #12
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    Thanks guys.

    it was the process itself that consumed most of the energy and creativity.
    Indeed. Better think twice than cut twice.

    Personally, with stays that short, I'd prefer a slacker head angle (~68), but that is me, not you.
    I know, the chainstays and bike is quite short and quite on the steep side.
    There are 2 reasons:
    -Love the quaterhorse from 2Souls-Cycles, which has a similar in geometry.
    - I spend a lot of time on my other (non offroad) bikes, which are all are very short and very steep. I am used to it and I love it. My Polobikes have 75° hta, 360mm chainstays, 940mm wheelbase. I know this is not offroad and not comparable. But till now my formula was: Look at the common standard and make it a little steeper and a little shorter and it will work out for you.

    Time will tell. First time I cycled offroad is just 2 month ago and Iīm gettin deeper into it every day. The terrain I ride is gettin heavier also. Wonīt be long till I built the next and different MTB for sure.
    (started framebuilding 22 month ago and this is number 8, so the forecast is, itīs less than 3 month till I start number 9 )

  13. #13
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    I'm liking the plate to the chainstay for chainring and tire clearance. How thick is it? Looks about 1"/25.4mm wide. It came out with good clearance for a 2x10, if that's the first time you tried it, you nailed it!
    cheers
    andy walker

  14. #14
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    Keep in mind that using plate for chainstay sections often results in a VERY flexy rear end. Depending on your taste, this can be totally fine or totally unacceptable, it just depends on the preferences of the rider.

    In this case there's enough space that the OP could probably have just used a conventional chainstay.

    But all that aside, this is the most impressive DIY tooling post I have seen in a while! Kickass!

    -Walt
    Waltworks Custom Bicycles
    Park City, UT USA
    www.waltworks.com
    waltworks.blogspot.com

  15. #15
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    Thanks for your comments.

    Andy: The plate is 1" x 1/4". I printed a pattern from the chainstay-sketch. Worked out better than I expected.
    This is an older template i made, changed it a bit before I made the chainstays.



    Keep in mind that using plate for chainstay sections often results in a VERY flexy rear end.
    Not necessary, when build proberly imho. As I said: This will be reinforced with a brazed box-girder for transverse rigidity. There will be only very little plate left unsupported. Made an FEM model and with the X12 and with the reinforcement there is absolutely no differnce in transverse rigidity.
    It will look similar to this lateron, but Iīll plan to make a hollow box-girder connecting the plate and the BBS:




    In this case there's enough space that the OP could probably have just used a conventional chainstay.
    No, not with plenty clearance for mud and 2.4 tires. At least not without crimping the hell out of the stays (see those chainstys from Christopher Henry - love his work but those stays scare me). Massive crimping might lead to fatigue problems in 5 or 10 years.


    It may seem Iīm a wisenheimer, sorry (indeed, I sometimes am ).
    I plan details of my projects a lot, often it keeps my from sleeping, which is a pain.
    Iīm a civil engeneer, designing, calculating and doing manufacturing control of huge steel- and composite bridges. So Iīm not that ingenuous concerning those stuff.
    Last edited by MiWi; 08-18-2013 at 11:56 PM. Reason: addendum chainstay plate

  16. #16
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    Not much work done today.
    Swapped the 29er wheels into my monstercrosser this morning and spend most of the day out in the woods. Quite funny to ride around on 29x2.4 tires on the cross bike. (tight as hell, only 2mm around each tire, just for fun today)




    The rest of the day I focussed on that 44mm headtube. Man, whe you are used to that 1.1/8 stuff, 44mm is really HUGE.

    Made a set of tapers for the jig.


    And purging heatsinks for that headtube.
    Last edited by MiWi; 08-20-2013 at 09:47 PM. Reason: wrong picture link of heatsink edited

  17. #17
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    Great stuff!

    My comment regarding flex comes from personal experience building a lot of bikes of both styles. I have never done an FEA of any of them, so we're coming at it from opposite directions. And as I said, that's pretty subjective so for most people it's not going to matter. Plate type stays are on all kinds of bikes and are working just fine, obviously. Just not my style when IMO it's easier to just use an oval chainstay.

    I regularly do 41cm chainstay 29ers with conventional stays and decent (65-70mm) tire clearance and not *too* much crimping. You could fit your tire with no crimps at all at 42.5 with most drivetrains, though 2x is typically the tightest.

    -Walt
    Waltworks Custom Bicycles
    Park City, UT USA
    www.waltworks.com
    waltworks.blogspot.com

  18. #18
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    It's funny, I thought the 44mm head tubes looked huge a few years ago but now they are on every bike I make, practically - 1 1/8 now looks weird to me!

    -Walt
    Waltworks Custom Bicycles
    Park City, UT USA
    www.waltworks.com
    waltworks.blogspot.com

  19. #19
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    I regularly do 41cm chainstay 29ers with conventional stays and decent (65-70mm) tire clearance and not *too* much crimping. You could fit your tire with no crimps at all at 42.5 with most drivetrains, though 2x is typically the tightest.
    Thanks for the information ! I think Iīll try that on one of the next bikes.
    (Though 65-70mm would be to tight for those 2.4 allmountain tires and the mud we got here for most of the year.)
    In fact it looked much tighter in the drawings, than it did now in real life. I was surprised how much clearance there is in the end.
    And with building the chainstay subassembly first, there ist no real risk. Tack it and put a wheel in it. If it doesnīt fit, do it over... Iīll try that. Thanks

    It's funny, I thought the 44mm head tubes looked huge a few years ago but now they are on every bike I make, practically - 1 1/8 now looks weird to me!
    Yes, is all about what you are used to I guess.
    I like the massive look of that short and thick headtube. Will be building more bikes with 44mm.

  20. #20
    will rant for food
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    That is good news for me Walt and MiWi, I find I can't make a suitably stiff bamboo frame without a massive 2 inch down tube, which makes a 1-1/8 fork look goofy. More of a marketing thing that I'm going to have to deal with in the future.
    Latitude: 44.93 N

  21. #21
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    Main triangle mitering pretty muc done.


    Next stop-> internal cable routing

    My plan so far:
    All four cables (both derailleurs, rearbrake and dropperpost) will be routed via the toptube.
    2 of them will be routed internally (still have to decide which two), the other two will be routed externally.

    Maybe brake and dropperpost internally. The two derailleurs externally with stops (not full length housing).
    Or I route the external lines for full length housing (no stoppers) so I got all the options which 2 to choose for the external routes.

    Any suggestions ?

  22. #22
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    Hey;

    If you are running two outside, I'd make it derailleur cables, since they need the most servicing. If you use full length housing, you even eliminate a lot of that.
    Most people ply the Well Trodden Path. A few seek a different way, and leave a Trail behind.
    - John Hajny, a.k.a. TrailMaker

  23. #23
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    If you are running two outside, I'd make it derailleur cables, since they need the most servicing.
    Good tip ! Thanks.

    If you use full length housing, you even eliminate a lot of that.
    Chose that way with my Monstercrosser and in fact they need very little service.
    My only disconcern is the look. Telling from pictures Iīd say thin inner wirer (with stops) under the toptube is more unobtrusive than thicker full length housing.
    Hmm, less servicing or better look....got some time left to think about that.

  24. #24
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    I'm not sure why you would bother running 2 cables internally and 2 externally. Do you think there's not enough room? If you ran the derailluer cables externally on the downtube it would make sense to me, since having the top tube clean for shouldering the bike occasionally can be nice. But I don't understand your motivation. I wouldn't mention this except you solicited input (though realize I'm not quite answering your question).

    Also, while I do agree with Trailmaker's suggestion given the circumstances--and if everything is mechanical-- I'd reconsider if your brake and/or dropper is going to be hydraulic. Just seems like a PITA to rebleed (though not undoable).

  25. #25
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    Thanks for the input.
    Shouldering is a thing to consider. Maybe not as much as with my cyclocross, but you never know....

    Brake is hydraulic, dropperpost mechanic.
    Bleeding is no problem for me. Did that on all my motorcycles regularly. The one-way bleeding from shimano makes it supereasy. Did that on my polobikes and had no problems.

    Reason for all 4 routings via toptube:
    Donīt want anything under my BBS (touchown on rocks, dirt/mud etc.).
    Beside that: Brake is upon seatstay, so routing with a slope down chainstay looks weird. Rear derailleur cable is also heading into the seatstay direction.

    Telling from ggogle picture search 80-90% of all allmountain-like hardtails route all cables on the toptube.

    Reason for 2 internally, 2 externally:
    4 externally on one tube looks way to chaotic for me. 3 would be okay, but 4 is to much for me.
    Its a 35mm toptube. 2 internally fits good, 3 is a pita, at least for me. Furthermore Iīm not feeling good weakening the tube to much. For me 2 internally is a good compromise (internal reinfocement of the holes will be added).

    2 Examples, want it just like that but a little cleaner looking.




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