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  1. #1
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    Frame numéro deux - fat for her

    So frame numéro un was put aside, to be completed later. With winter coming, frame numéro 2 as taken shape in December with most of the work happening during the last 2 weeks. It is a fat bike, size small, for my girlfriend.

    Geometry is as followed:
    Frame numéro deux - fat for her-numero-deux-geometry.jpg

    Design specs were:
    135mm rear spacing, 17.5mm offset on drive side
    Built around Surly Pugsley fork with 100mm front spacing
    Designed with clearance for Nates on 80mm rims
    2x10 drive train with e-type front derailleur
    100mm BB

    Tube set is:
    NOVA 29er CrMo Tubeset with 35 mm x 858 Downtube
    HT: 36mm 1.1
    DT: 35mm .8/.5/.8
    TT: 31.8mm .8/.5/.8
    ST: 28.6mm .9/.6/1.2^
    CS: 30x18mm tapered and pre bent (but I add to rebend them)
    SS: 16mm tapered straight (I add to bend them)

    This built was a LOT more challenging then my first project. Fat bikes have the extra challenge of squeezing the fat tires, CS and crank together. I had to make myself some bending apparatus for massaging the tubes into shape. I used an exhaust pipe bending press and made some wood forms with a router and supports with scrap metal I had laying around.

    Frame numéro deux - fat for her-pc090012.jpg

    Frame numéro deux - fat for her-pc090013.jpg

    All in all, the bending went *OK*. 16mm Nova SS are VERY easy to bend with no wrinkling at all. I started with straight SS and filled them with water and let is freeze to prevent kinks but I think it was unnecessary (for the SS). The most pronounced bent was 55° on the non drive side.

    The CS were another beast... I did the filled with ice thing and was able to get part of the way with no kinks/wrinkles while keeping the width of the original CS (i.e. no dimpling). I did ruin a CS as it developed a kink. I was able to get a 30° bent in them (from the original ~12°). More than 30° would required some local dimpling to prevent kinks. YMMV.

    Cutting, filling, mitering and brazing went OK. I used paper templates for the miters and I also printed 1:1 scale views from the 3D CAD model to ensure that all components were where they needed to be (especially in the BB, CS, crank, tire area). I had the rear wheel and crank at hand also which was also very helpful to double check clearances before laying the final fillet.

    Oh I did run into a problem with the seat tube! I choose the shortest available seat tube with the kit. When I cut the tube to length, I looked at the wall thickness and it looked pretty thin...

    Frame numéro deux - fat for her-pb240007.jpg

    I was past the .9 section and event the transition. Maybe I could have brazed it as is and it would have been fine but I did not feel too confident about it. So I fished a piece of tube from my Air Spruce practice box that was 31.8mm OD with 0.065" wall. I filed the ID until it fitted the 28.6mm OD seat tube, brazed that short tube to the BB and called that a lug for my seat tube! Time will tell if it lasts!

    Frame numéro deux - fat for her-pb240009.jpg

    Frame numéro deux - fat for her-pb240011.jpg

    Finishing/filing/sanding fillet is not a step to underestimate time wise! Granted, my fillets are far from perfect and require more work to get them to look nice.

    I'm satisfied with the final result! As so is my girlfriend with her Xmas gift. Now I need to sent it to the LBS for some finish cleaning, reaming and tapping. It will probably stay raw for the winter as she wants to ride it ASAP!

    Frame numéro deux - fat for her-pc290034.jpg

    Frame numéro deux - fat for her-pc290035.jpg

    Frame numéro deux - fat for her-pc290037.jpg

    Any comments or questions, feel free! More pics when I assemble it.

  2. #2
    Harrumph
    Reputation: G-reg's Avatar
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    Very nice for a #2. That's a good call on the sleeve for the ST. The brazing masters wouldn't braze .6 into a thick BB shell and a 1mm-ish DT and expect it to be long lived. If you use an externally butted ST and use the thick butted end at the BB you can cut the top to nearly any length if you use a sleeve on the top.

    I was nearly going to do a similar build for the same guy I built #7 to replace his Pug. The idea was to replicate the fit from #7 with 2x10/Pug offset 135 rear/100 Pug fork/DM FD/Dynohub/Marge Lites/Unstudded-Dillingers. He decided to RUN the AH135 this year so it's postponed but could/will be a very nice bike. Just using nice steel with no other changes would make a big difference.

    Are you going to get away with 2x10 and Nates/RDs? And why use an E-type on a clean sheet build? No offense, I just personally hate those things, and the 2x10 direct mount FDs work so well.
    I like those 100mm Pug forks, it's a battle to get the wheel in and out past the brake caliper with 80mm rims.
    Slowly slipping to retrogrouchyness

  3. #3
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    Ditto G-reg,

    Good clever thinking on that ST/BB sleeve.

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

  4. #4
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    Quote Originally Posted by G-reg View Post
    If you use an externally butted ST and use the thick butted end at the BB you can cut the top to nearly any length if you use a sleeve on the top.
    Great suggestion! Hadn't tough of that. And I like how a ST sleeve create a truly "custom/hand built" signature.

    Quote Originally Posted by G-reg View Post
    Are you going to get away with 2x10 and Nates/RDs? And why use an E-type on a clean sheet build? No offense, I just personally hate those things, and the 2x10 direct mount FDs work so well.
    I like those 100mm Pug forks, it's a battle to get the wheel in and out past the brake caliper with 80mm rims.
    Good point, I'm not sure exactly if a full 2x10 drivetrain will fit with Nate/80mm rim (flattops) - probably not. This bike will initially ride on Endo/Larry so no problems. The idea was to be able to FIT Nate in the frame and deal with any drivetrain issues if necessary (shim cassette outboard and remove a cog or 2).

    E-type; simply because I have the derailleur handy! This bike will inherit the components of my current 2009 907 fat bike (which is e-type, 135 offset). Wheel set, drivetrain, fork, etc. will be transfered so I designed accordingly to keep the build cost down.

    Personnally, I like the look of the e-type. The derailer seems to "float" beside the chainrings. I don't like how the problem solver adaptor brings the housing out from "behind the ST". And I find a welded/brazed direct mount creates a discontinuity in the ST line. IMHO. But these are preferences, they are all functionnal.

    So this brings the question, "Which fat bike will you ride if you take apart your current 907"?... Stay tuned for the "frame numéro trois" thread!

  5. #5
    J_K
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    Nice work!
    I'm not a fan of the offset rear ends, but have done it nicely.

  6. #6
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    Some more pics of frame numéro deux. I hope to have it assembled in "proto mode" (i.e. unpainted) by next week end to test ride it.

    Frame numéro deux - fat for her-dsc_0017.jpg

    Frame numéro deux - fat for her-dsc_0004.jpg

    Frame numéro deux - fat for her-dsc_0014.jpg

    Frame numéro deux - fat for her-dsc_0006.jpg

    Frame numéro deux - fat for her-dsc_0007.jpg

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