The first hint to a bunch of tubes becoming a bicycle frame is when all of the tubes are cut and assembled in the jig. One of our first investments was in a top of the line framebuilding jig. We chose the new 2011 Sputnik Frame Fixture for a few reasons…
One big reason we chose this jig was that it was built by our friend Jeff Buchholz, the founder and sole maker behind Sputnik tools. Both Jamie and I worked alongside Jeff many years ago at Independent Fabrication. Jeff was one of the original founders of I.F. and found his love making tooling there. He made most of the tooling for them and through the years Jamie and I became quite comfortable working with his various framebuilding inventions. Another reason we chose this jig is that we’ve found that Jeff’s tools hold up well over time and remain true and accurate throughout many years of heavy use.
The jig didn’t come with a stand so we had to build one. A sturdy stand, with wheels. So we made one out of 3 inch steel tubing and mounted it to locking casters on the bottom. The tripod design was a good solution for our rolling jig, especially given the slightly uneven floor in our workspace. We learned this trick from using another great American made frame jig, the Anvil Supermaster. That jig came with an “assemble yourself” steel stand that had a very similar tripod style base to the one we made here. It worked so great, we applied the same principle to mounting this jig. Now the jig is sturdily mounted and mobile, perfect for our space.
Just like our alignment table, the Sputnik frame jig bases the alignment of the frame off of the drive side of the bottom bracket. Everywhere the tubes of the frame are secured to the jig there is a purge line that allows argon to flow into the frame, displacing the ambient air that could contaminate the frame when we actually tack weld the tubing together. Seeing that all we are making are stainless steel and titanium frames, this feature is a requirement, it’s not a bad idea for regular steel frames either.
The seat tube angle is easily set with the degrees scribed directly to the jig, making setup a breeze.
On the top of the seat tube pillar is the adjustable securing device that holds any length seat tube precisely on center, while also purging the frame.
Through a few calculations that we worked into our frame formulas we can set the head tube height and top tube length based on the numbers on the jig. The result of this calculation sets the bottom of the head tube at the proper height. The Cliff Notes version of how this works is: The bottom bracket position is fixed on the jig and the distance that your rear dropouts are above the bottom bracket (drop) varies per bike. So that means that you have to adjust the bottom of the head tube accordingly in order to get the front wheel’s axle in the right place.
The head tube angle is then set the same way as the seat tube angle.
This tower adjusts the dropout height in relation to the bottom bracket. It also slides back and forth to adjust chainstay length.
This is the first of many steps that ensures that the assembled frames we make are straight and the geometry is accurate.
More to come, stay tuned…