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.

Quote:

And you did in a most verbosemanner. I can't decipher your ramble butit appears you have made a very simple engineering concept intogobble-de-gook.

As I was introduced to the simple view of frame alignment40ish years ago too. But you know, we learn and can understand the greatersubtly as we go forward and listen to others who are smarter then we are. As Ihave. It was a few handfuls of years ago that I first heard of the separationof the steering/tracking alignment from the bio aspect. It made a lot of sense,some of which I had experienced with the frame I built just before theEisentraut class (this was the one I referred to with a badly twisted shell but"perfect" handling).

Initially in my frame working (before I actually brazed thefirst one) I did all my aligning WRT the BB shell. My really bad shelled framedrilled the point home in an uncomfortable manor. That both a steering/trackingalignment and a bio one were needed for a complete frame/fork. I just didn'thave all the needed foundation yet to truly understand how it all ties intogether and at the same time is separate.

I used the campy straight edge in the beginning (did youknow that the straight edge was just so wide as when placed against a 70mmshell face it's other edge would graze the inside of the 120mm spaced rear dropout?). next up was clamping the shell's face to a flat surface, back then thiswas a piece of Mic6 AL plate. Now I could start to control the main frame tubesincluding the top tube. But a 3/4" thick plate large enough to allow theframe to be checked is both heavy and subject to gravity in not well supported.Around this time the NECA alignment system came onto the market. Somehow I feltthat running the alignment through a bearing (with little aligning support init's self) wasn't a very repeatable process. (And my discussions in later yearsconfirmed this as far more experienced builders told me of their frustrationwith this system).

In the early 1990s my late wife gave me a really cool gift,a proper cast and hand scraped precision flat surface. Now my measuringreference would be far more consistent. A dial indicator later and I could seethousandths of an inch. So what did I learn? That reclamping a frame on thesame side of the shell resulted in different readouts and that flipping theframe had even larger differences. (This is after facing with campy BB tools ofcourse). I went on to measuring a lot of frames over the next few years. I sawthe measurements of shell to tube alignments changed with each reclamping. Isaw frames with no known handling issues having easily measured Bb twist. I sawtubes that were not straight on bikes with wheels in proper plane and shellspretty well aligned WRT the ends of said tubes. I learned that because youcould see thousandths of an inch didn't mean that much sometimes.

A Bb stand off post (sometimes called a "whipping post)that was both hardened then surface ground aided my handling the frame aligningstuff. Machinist's jacks, steel leverage bars, head tube centering cones allmade the checking and bending of a frame far easier and more controlled. And Ibecame happy, feeling I had at last found my method and understanding. By now Iwas separating the shell's alignment from the frame's steering/tracking one.(Although I had yet to put this into words, it was a conception/a theory I wasworking not having to talk about it to others).

I was measuring the seat tube's slant WRT the flat surfaceover a known distance then comparing this to the headtube's slant over the samedistance. I knew that since the clamping of the shell was a variable I neededto get past that and instead create my virtual plane of reference. I still usethis method during my actual bending of a frame into alignment.

Then along came Keth Bontrager, Jamie Swan, Kirk Pacinti(and a few others) who posted the idea of fixturing the head tube to the flatsurface via a through rod/cones and single point supporting the seat tube. Wow!years of my understanding and evolving practices came into focus. I soon hadsuch a tool (thanks Alex Meade). Now i found that my repeated reinstalling aframe had far less drift from each measuring session.

They (and I apologize if I have the names wrong) separated the shell's alignment from the restof the frame. This is not discounting the need for either shell based aligningor headtube fixed alignment being properly done. This doesn't make one better ormore important then the other. But it offers a tool, a view, an understandingto how what at face value seems to be a simple goal is really a more complexsystem.

But there is more then two ways to skin the alignment cat.Some builders (and one who is known for his frequently red bikes) chose to workoff the shell face. But they use but one side during the building process. Theymight even only face once after the shell is fully brazed. They allow for otherrealities to exist if they were to check for them (and I hope I have described their method properly). I prefer to explore and findmy method and understandings.

I will end with the claim that shell based alignments do thesame thing that my methods aim to do. All aspects of alignments are in order,all components, the rider are centered/planar/symmetrical (unless designs callout otherwise and it does happen), the handling is consistent, the fit isagreeable. The guy who does my painting, and who has taught hundreds ofbuilding students for decades, uses the methods I do but with a slightdifference to check for frame straightness. He places a frame's seat tube andhead tube on parallels on the flat surface to find rock. No shell clamping. Yethe uses the shell clamping during his building process.

This long winded post started as a rebuttal to XXX’s reply to my earlier post defining the aspectsof alignment and how they are different from each other yet do interact. I hopehe and others now have a fuller understanding to my views. Andy.