Prototyping Bike Dropouts

I want to build a custom bamboo bike frame. The essential pieces for the frame besides the bamboo includes a metal head tube, a metal seat post insert, a metal bottom bracket tube, and the metal rear tire dropouts. To keep things simple, I will make a track bike which has different styled dropouts than a road or mountain bike. Since my bike frame geometry may be unique for a track bike, and since the dropouts have to be longer than average in order to attach them securely to the bamboo seat and chain stay tubes, I decided to make my own dropouts. They will first be prototyped in plastic from the MakerSpace 3D printer, then CNC routed by a friend's personal metal CNC router. 

This process required me to design and sketch out the bike frame geometry onto blueprints, use that as an underlay in Adobe Illustrator (AI), create the 2D design, convert that to a 3D file, print out in plastic, check for size, and reiterate as necessary until the 3D file is ready for metal routing. 

I hand drew the bike frame geometry onto butcher paper, copied from an old bike frame we had laying around. I used an angle gauge, calipers, and a ruler. This resulted in a to-scale design of the bike I will make. 

I downloaded a camera level on my phone to ensure that the photo I took of the blueprint was straight on from a 90 degree angle, so that when I was using it as a drawing guide in AI the angle would be correct. The angle from the seat stay to the chain stay was about 70 degrees. 

I made a few designs in AI. The basic requirements of the dropout were a 10mm diameter slot to fit the average rear wheel axle, and a 70 degree angle with notched arms that extended about 2 inches. I exported the SVG file into 123D Design, and extruded the 2D piece an eighth of an inch into the 3rd dimension (or along the Z-axis). I exported the file as an STL and loaded it onto our 3D printer's computer. 

After printing it out and trying to fit it to a bike axle, I realized it was a bit small. I checked the slot width in 123D Design and saw it was only about 9.5mm! I needed it to be 10mm. I realized the line I drew in AI had a certain thickness which resulted in the addition of a few extra millimeters along the perimeter of my piece. So I offset the line to be on the inside of the line path, until I got the 10mm diameter I needed. 

The next step will be seeing how the CNC metal router handles the digital file, and learning AutoCAD so I can more easily edit my digital design, create more complex 3D objects, and not worry about formatting issues between programs.