Color us impressed. Reddit user ‘bcmanucd‘ has just shared his process on the trending /r/DIY subreddit of creating a time trial bike for his wife using his university’s engineering shop. While it’s unclear what his design or engineering background is, one thing is for certain: the dude can build a pretty impressive bike!
Here he shares his process:
In 2009, my wife (girlfriend at the time) was racing on our college’s cycling team, and needed a time trial bike to compete at the national championships. I was finishing my master’s thesis, and neither of us had a lot of money, but I had a lot of free time and access to the college of engineering’s machine shop.
I wasn’t satisfied with the half-assed budget TT bikes of the day, so I offered to design and build her a bike. It turned out to be a very lengthy, involved process, but I learned a whole lot from it, and it helped her win the women’s team time trial national championship that year.
The geometry was based on a fit assessment from her coach. The position is very aggressive, and necessitated a head tube length of 85 mm including headset. I drew up a sketch of the frame in Autodesk Inventor, and then attached an assembly of modeled tubes to the sketch.
The model in Inventor was crucial to the development of the design, as it allowed me to analyze clearance issues (i.e., crank and chainring clearance with the chainstays). I was also able to use the tubing profiles to create NC programs for tube mitering and milling of the dropouts and head tube, for example.
I chose to use 7005 aluminum alloy, as it would not require solution heat treatment. My suppliers were Nova Cycles of Rocklin, CA and Fairing Industrial of Chino, CA. Each tube had a unique cross section, so I used a Mitutoyo coordinate measuring machine (CMM) to measure tube shapes. This is the down tube. The CMM recorded x and y coordinates for the surface at every millimeter, and I was able to import this data into Inventor.
I wanted the head tube to be both short (for the fit) and narrow (to reduce frontal area). I designed the head tube to accept an integrated headset and a 1″ steer tube. This got the diameter down to 42 mm on the ends. with some intricate surface milling I reduced the width to 35 mm in the middle.
I couldn’t find a head tube reamer for a 1″ integrated headset, so I made this reaming insert for a VAR headset reamer & facer. I used 4140 steel and had to resort to hand filing for the reliefs to get good cutting surfaces.
The dropouts with set screws installed. This allows a convenient way to adjust the spacing of the rear wheel behind the seat tube. Note the knurling impressions on the right dropout – I clamped the dropouts in a rear wheel to do a frame mockup to check clearance on the rear brake and cable routing.
Mitering the top tube. I used FeatureCAM to write NC programs for the tube miters based on imported Inventor parts files. The clamps holding the thin-wall tubes were also cut from FeatureCAM programs based on the tube profiles from the CMM.
The bottom bracket joint, coming together. I had to do a mockup of the rear wheel, frame, and rear brake to determine the optimum shape for the opening in the down tube for cables to exit. This required several iterative cuts of the down tube’s bottom joint.
This chainstay bridge plate also served as the mounting point for the rear brake. I replaced the mounting stud on the Oval Concepts aero brake with a bolt, and threaded the hole in the plate. I rotated the seat tube out of the way for this photo to illustrate the upper side of the plate – note the rib reinforcing the bolt hole.
The head tube junction. I filed off the contour lines on the head tube later, which helped with the fit. Notice the hole in the top tube near the trailing edge of the down tube. I cut holes in the top tube to route the cables through the frame, entering behind the stem. I inserted an unused portion of the seatstay in the top tube to reinforce these holes.
After completion of the welding (and the day in the oven), I started a lengthy process of sanding down the joints and building them up with Bondo body filler. It was meant as an aero bike, not a light bike, but the total frame weight before paint was 2.75 lb. Not too shabby.
Here’s a shot of the bottom bracket area. you can see the placement of the rear brake a bit better. Adjustment of the pads isn’t easy with the cranks installed, but this was never a bike of convenience.
Back to painting. I resumed with several layers of high-fill primer (with delicate sanding in between), a white top coat, a blue fade done with an airbrush, and a few layers of clear coat to get things glossy. We then cut masks from Contac paper (a lovely wood-grain pattern).
The final step was a few layers of flat black enamel for a durable finish. I used Dupli-Color automotive paints throughout, as I’ve been dissatisfied with common hardware store rattle cans in the long run.
As he mentioned in the introduction,”…it helped her win the women’s team time trial national championship that year“……If this isn’t true love, then I don’t know what is.