I start this thread as a spin off from a Bike Mechanics interaction where I was questioned about my description of bike alignment by another poster. This was a tangent to the OP thread. So I have copied and pasted my questioned post here for more experienced builders to comment on. Below is my first post. I will leave the questioning poster's name out for now.
Posted earlier 10/2/16 -
There are a few aspects of frame alignment that we could talk about.
The "tracking" alignment is when both wheels are placed in the same plane with each other (when going straight ahead). "Steering" alignment is when the frt tire contact patch, with the road, is in line with the steering axis and said axis is also coplanar with the ft wheel's plane. These two are usually grouped together for most discussions.
"Component" alignment usually refers to the BB shell, the head tube and fork steerer being coaxial, perpendicular and parallel WRT their axis and faces. This is what a set of frame finishing tools do (as in chase and face the shell, ream and mill the headtube and crown race). But also things like brake mounting holes being parallel to the wheels' planes, rear der mounts being perpendicular to the rear wheel (or whatever it takes to have the cage parallel to the cog set's plane), ft der braze on mounts properly located and even seat tube ID being round and straight cylindrically.
Then there's the "Bio" alignment. This is usually thought of as the BB shell being perpendicular to the frame's plane and centered WRT this plane. But the seat tube and head tube being planar to the frame's plane also is a part of the fit alignment. The seat and bars are centered and straight here too.
It doesn't take much imagination to see that these different alignment aspects overlap with each other to certain degrees. Also that some can be off with others spot on and that some people will claim the frame is straight or it's not so. I've made a frame where the tracking and steering alignment was very good yet the shell was twisted so badly that my knees felt it.
It's the goal of a builder to work all these alignments to a state where they fall within the human's ability to assemble the bike with the speced components in a good adjustment/function condition, to have the rider's body fit the bike so that they can ride efficiently without any more discomfort then tolerated and have the bike (which is more then just the frame/fork) track/steer/handle in a consistent and safe manor. But the rider, the builder AND the bike's parts (including tubes, lugs, shells, crowns) are never completely perfect. There will always be some deviation from the ideal. Tubing usually has some bow or non straightness when rolled on a flat surface prior to mitering as example and this bowing isn't always only in one plane (as in one butt transition can make the thick end bow up when the other butt causes it's end to go right).
Which brings me to a story about the perfect frame. When I attended the last east coast Eisentraut building class (1979 in Rutland VT) many of the students brought their work to Al and asked "is this right". After a few days one could see the frustration in his eyes as he repeated his advice/instructions over and over. Finally he stopped and brought us all together to say that there is a "good enough" point after which any more "improvement" makes no difference. He pointed to a student and said that he (the student) had one leg longer then the other, another had shoulders of different widths that most of our feet were slightly different in sizes. He then offered "find me a perfect person and I'll build a perfect frame". Which by then we understood was never going to happen and we went back to out work benches to try to find that "good enough" point in our work. Andy.
