Track Bicycle Frame 001
For my senior thesis project at MassArt, I built a steel track bicycle all the way from design to welding.
Geometry & Design
The geometry for the bike was a combination of numbers from several track bikes I had ridden, primarily a Cinelli Supercorsa Pista, All-City Big Block, and a Cannondale Track.
I used Solidworks to mock the bike up, but switched to BikeCAD when it came time to nail down the final geometry and print my working shop drawings.
It was at this time that I selected the specifications for the tubing I’d be using. Diameter, shape, wall thickness, and butting can all make a huge difference in the weight, look, and character of a completed frame. I settled on Columbus Zona tubes, with a .9mm wall thickness which thins out to .6mm in the center of the tube.
With milling and filing completed, the frame fit up nicely in the jig with no gaps.
Each process builds on the one before it, so to get a frame that is straight and strong the frame has to be mitered well with minimal gaps. This was by far the most time consuming part of the project, and required hours of “conversational” hand filing — place the tube in the jig, note any high spots on the miter, file a few strokes off, and repeat.
Milling and Fitup
Before making any cuts I set my framebuilding jig (right) to exactly the right measurements. To begin construction, I notched the tubes using a Bridgeport milling machine to fit together within a half a milimeter of tolerance. Once notched, I fit them one by one into the jig and hand filed any remaining cuts.
I used several 3D printed jigs to aid in the more complicated cuts such as the chainstays (pictured below), which I cut in tandem.
By beginning my weld at the downtube, I’m able to keep an eye on the alignment of the seat tube and head tube, which are the most important parts of the bike to keep straight. If they are welded crooked, the bike will pull to one side while riding.
Finally, by tacking in my top tube and seatstays, I locked in the alignment of the bike.
Welding and Alignment
Effectively TIG welding a bicycle frame is tricky. While it may seem that the jig would hold everything steady, when the intense heat is applied the steel actually wants to warp and move. Because of this, the order in which the tubes are welded in place and the alignment in between welds is extremely important.
Between each tack and weld, I took the frame to the alignment table and gently bent it back into alignment. I used a frame alignment gauge and a dummy axle to ensure alignment of the rear traingle, where the wheel sits. By paying attention to my alignment, I was able to use the heat distortion of the welding to “pull” the frame into perfect alignment.
All that was left to do was fully weld up the frame, checking alignment as I went.
While a brake bridge is not strictly necessary given that there are no brakes to mount, I shaped and welded one in anyway.
Similarly, I tapped and faced the bottom bracket threads to ensure easy and straight threading of the bottom bracket.
Final Shop Tasks
Drilling vent holes ensures that the interior of the entire bike is one envelope, with easy exit points for moisture to prevent rust.
The intense heat of welding warps the headtube in tiny imperceptable ways that can cause issues with the headset bearings, so I reamed and faced the headtube in order to ensure that every surface was perfectly square.
The completed frame leaving massart, ready for powder coat.
Frame and fork before baking. Just like glazing, the color of the powder does not come out until heat has been applied.
Finishing
Pike Powder Coating did an excellent job on the finish of the frame and fork. Powder coating is a process not dissimilar to glazing in ceramics, where a powder is attached to a metal surface, then baked into a durable and uniform surface.
