Fat Bike Fabrication at Metal Guru, Part 2

Arriving at Metalguruschool on July 1, 2013 – www.metalguruschool.com

Tube Selection

After going through the safety procedures, geometry, CAD and types of steel alloys, we moved on the tube selection for the main triangle.  The following front triangle tubes were selected for my Fat Bike fabrication:

  • Top Tube (TT) – Dedacciai DT tapered 31.7mm – 28.6mm
  • Down Tube (DT) – Nova Cycles bended tube, CroMo 38.1mm
  • Seat Tube (ST) – Columbus Cyber Mtb 28.6mm, 1.2/0.6/0.9
  • Heat Tube (HT) – Paragon 44mm
  • Bottom Bracket Shell (BB) – 100mm

We decided to go with the bended DT primarily due to configuration of the White Brothers’ Snowpack Fork to achieve the clearance between the fork and DT as shown on the bike CAD:

                CADTubes Inspection 

What I learned was that tubes are not perfectly straight.  This could be determined with the dial indicator or by rolling tube on a flat surface such as granite or steel plate.

Mitering Front Triangle

To determine the hole saw diameter, you need to measure outside diameter of the following tubes.  In my case I had the following measurements:

  • ST – 1 3/16”
  • HT – 1 7/8”
  • BB – 1 1/2”

Determine the miter angle between two tubes and the stop length, which could be obtained from the bike CAD.

TT Mitering

ST Mitering

DT Mitering

Seat Tube Compression Slot

  • ST slot could be machined on a vertical mill with 1/8” end mill
  • Determine slot distance from the top of ST to the center of the hole.  I used 3/4”
  • Slot width and hole diameter, 1/8” and 3/6”, respectively

Stay Slotting for Dropouts

Slotting Chainstays

Slotting Seatstays

Dirlling H2O Boss Holes & Vent Holes

H2O Boss Holes Drilling

Drilling Vent Holes

Delicious Lunch at Hokkaido with Carl after hard work

Lunch at Hokkaido after hard work!

Tack Welding the Frame

Tack Welding 1

Tack Welding 2

Tack Welded Frame in the Jig


Welding the Frame

Welding 1

Welding 2

Welding 3

Welding 4

Welding 5

Welding 6

Frame Alignment

Frame alignment is checked few times during the welding process as following:

  • after tack welding
  • after HT is welded
  • after ST and BB shell are welded
  • after Bridges are welded
  • after dropouts are welded

Brazing H2O Bosses and Cable Guides

Brazing H2O Bosses

Brazing Cable Guides 1

Brazing Cable Guides 2

Brazing Cabel Guides 3

Finished Welded Frame

Troika Finished Frame

I decided to have Vicious Cycles to paint the Fat Bike frame, which will be discussed in more details in the next blog post.

– Vlad