The Concept
Having done a little research I've come to the conclusion that feeling as if you're not prepared is OK when embarking on a project such as building your first bicycle frame and fork. I suspect the best way to get started is by taking a one or two week course from an established frame builder but for me that is not an option right now so I got started by reading up on the subject. "The Paterek Manual" and "Designing and Building Your Own Frameset" are great resources.I've been "tooling-up" over the last couple months and at the same time I've decided that the bicycle should be suitable for commuting, light touring, and rough or unpaved roads. I want the option of running 35mm tires, fenders, and racks. Also, I hope to re-purpose any old bits I can from the bicycle parts boxes in my basement. They go back thirty years and I need to make room for some new stuff.
The Drawing
I wasn't in a big rush to get this done as I figured if I mess this up badly it's going to cost me a lot of time and resources later. The concept was clear so now I needed to gather the data needed for proper fitment. I know the ratio of my torso to leg length, and the ratio of my femur length to leg length is not "average". This genetic predisposition appears to be favorable to cycling but it also means an off-the-rack frame may not be optimal. An online search of methods for fitting bicycles to people left me with the impression that this craft was part science, part art, and part personal philosophy, but I suspect the foundations for most methods came from the CONI manual. I decided to start the drawing using the instructions from The Paterek Manual. I took some measurements and came up with a seat tube of 41 cm and top tube of 49 cm and I confirmed by measuring several bicycles I'm comfortable riding that somehow I had messed up already.
A different approach was required. I reviewed what had worked for me in the past and what needed to be different for this bike based on my experience and bio mechanics. It would have 700c wheels and 170 mm cranks. Compared to my road race bike (seat all the way back with 130 mm stem on a 51 cm frame) the top tube would be slightly longer, and the seat tube and head tube angles somewhat more slack. The new dimensions would be ST=50 cm and TT=55 cm. Based on this the drawing was progressing nicely until I got to penciling in the down tube at which point my head tube disappeared as the down tube and top tube came together. Oooops, for a lugged frame that's a showstopper.
After a little more research which involved checking up on the geometry of other touring frames such as the Dawes and others I settled on some compromises which would allow me to still use my lugs. I gave up stand over clearance and tire clearance while retaining the ability to run a 35 mm tire with fenders. I sloped the top tube 2 degrees raising my bars a bit, this actually seemed more desirable for touring. The drawing was updated and voila; the head tube reappeared and at 13 cm was just long enough to acommodate my lugs.
This is what I ended up with.....
BOTTOM BRACKET DROP 7 cm RECOMMENDED RANGE 5-8 cm
SEAT TUBE ANGLE 73 RECOMMENDED RANGE 72-76
SEAT TUBE LENGTH 52 cm
TOP TUBE LENGTH 55 cm
HEAD TUBE ANGLE 72.5 RECOMMENDED RANGE 70-75
FORK RAKE 4.8 cm
TRAIL 6 cm RECOMMENDED RANGE 5-6.5 cm
FRONT CENTER 59 cm RECOMMENDED 58 cm
A different approach was required. I reviewed what had worked for me in the past and what needed to be different for this bike based on my experience and bio mechanics. It would have 700c wheels and 170 mm cranks. Compared to my road race bike (seat all the way back with 130 mm stem on a 51 cm frame) the top tube would be slightly longer, and the seat tube and head tube angles somewhat more slack. The new dimensions would be ST=50 cm and TT=55 cm. Based on this the drawing was progressing nicely until I got to penciling in the down tube at which point my head tube disappeared as the down tube and top tube came together. Oooops, for a lugged frame that's a showstopper.
After a little more research which involved checking up on the geometry of other touring frames such as the Dawes and others I settled on some compromises which would allow me to still use my lugs. I gave up stand over clearance and tire clearance while retaining the ability to run a 35 mm tire with fenders. I sloped the top tube 2 degrees raising my bars a bit, this actually seemed more desirable for touring. The drawing was updated and voila; the head tube reappeared and at 13 cm was just long enough to acommodate my lugs.
This is what I ended up with.....
BOTTOM BRACKET DROP 7 cm RECOMMENDED RANGE 5-8 cm
SEAT TUBE ANGLE 73 RECOMMENDED RANGE 72-76
SEAT TUBE LENGTH 52 cm
TOP TUBE LENGTH 55 cm
HEAD TUBE ANGLE 72.5 RECOMMENDED RANGE 70-75
FORK RAKE 4.8 cm
TRAIL 6 cm RECOMMENDED RANGE 5-6.5 cm
FRONT CENTER 59 cm RECOMMENDED 58 cm
The Jigs
I once read that real cyclists build their own frames. A good philosophy to aspire to, but a big challenge in practice. How do you keep tolerances to a within a fraction of a millimeter when joining frame materials? At my skill level I would not even attempt to join the frame materials without some way of fixing them in place because a series of a few small errors in alignment could easily make the bike unrideable. However, a beautiful Henry James' Universal Jig is simply not in the cards so I went back to Richard Talbot's book for inspiration.
With some 3/4" plywood and an old gear puller reconstructed to serve as a blade clamp I came up with a fork blade mandrel prototype. Not sure how long it will last but it worked fine for raking these forks. With a similar approach, a little ingenuity, and some old front hub parts I built the fork jig. I'll keep a fire extinguisher handy for the brazing. The main triangle jig cost me $35 in C-clamps which I modified to clamp the tubes without dimpling them. If any of my tube lengths or angles change during this process I will have to modify or possibly rebuild or create new jigs but this is good enough for the first frame.
With some 3/4" plywood and an old gear puller reconstructed to serve as a blade clamp I came up with a fork blade mandrel prototype. Not sure how long it will last but it worked fine for raking these forks. With a similar approach, a little ingenuity, and some old front hub parts I built the fork jig. I'll keep a fire extinguisher handy for the brazing. The main triangle jig cost me $35 in C-clamps which I modified to clamp the tubes without dimpling them. If any of my tube lengths or angles change during this process I will have to modify or possibly rebuild or create new jigs but this is good enough for the first frame.
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Fork Blade Mandrel |
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Fork Jig |
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Main Triangle Jig |
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