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:
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
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.
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...
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!
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!
Any comments or questions, feel free! More pics when I assemble it.
Mtbr's 2016 Winter Biking GearReviews and Roundups
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Thread: Frame numéro deux - fat for her