I appreciate Kurt's comments and expertise but sometimes a low tech approach is adequite or necessary.
The issue of the tubes being out of alignment themselves is exactly what I meant when I said "and is an ESTIMATE (about three steps removed) of alignment to the plane formed by the centers of those tubes" [emphasis added], the steps being the alignment of the tubes relative to each other, the concentricity of the tubes and the straightness of the tubes.
I would disagree about the "the string test only being effective if ...". In fact, the string test will give a pretty good average even if the tubes are skew since the measurement is in the middle. From a practical sense it is very valuable. Many framebuilders never had access to an alignment table and some not even to a jig. Yet they built well aligned frames with simple tooling and methods. Repairs can be done with the same simple methods.
I would agree that "the best results come from using an alignment table and a competant frame builder". I used to bring forks up to Matt Assenmacher at least twice a year because I couldn't begin to approach his tooling or experience at increasing rake etc.
As to e-richies comment- it is an ugly process at best. Just start regularly sighting down seat stays, even on supposedly unspread bikes, for some real surprises.
Joe B-Z
GNNJ
<classicrendezvous@bikelist.org> Sent: Monday, October 14, 2002 5:57 PM Subject: Re: [CR]Cold setting alignment
> The string method will only tell you if something is askew with the
> alignment. It won't tell you what is out of alignment. The string method
> is only effective if one can confirm that the head and seat tubes are in
the
> proper plane. Then measuring the string's gap from the seat tube will
> accurately define the stays symmetry or lack thereof. A rear end can be
> spread any old way you want but the best results come from using an
> alignment table and a competant frame builder.
>
> Curt Goodrich
> Minneapolis, MN
> ----- Original Message -----
> From: Joe Bender-Zanoni <velo531@hotmail.com>
> To: <classicrendezvous@bikelist.org>
> Sent: Monday, October 14, 2002 2:29 PM
> Subject: [CR]Cold setting alignment
>
>
> >
> > Dale said:
> >
> > You do have to be very careful to set it correctly so the frame remains
> > symmetric. That is the same amount of change on each side.
> >
> > A Campy straight edge tool is very useful here. ...
> >
> > ______________________
> >
> > A string can also be used, tied to each rear fork end and looped around
> the
> > head tube. Make sure the string leave the fork ends symetrically. Then
> > measure the gap between the string and seat tube on each side. I use a
> > caliper to measure. It is surprisingly accurate. It is also shocking how
> > poor the alignment is on many frames.
> >
> > These two methods have slightly different datums for alignment. The
> straight
> > edge method aligns to the BB shell and should optimize the chainline.
The
> > string method aligns to the head and set tube and is an estimate(about
> three
> > steps removed) of alignment to the plane formed by the centers of those
> > tubes. If both methods don't agree you've got some bigger problems. Some
> of
> > the most cronically baffling shifting problems turn out to be BB shells
> that
> > are askew.
> >
> > Joe Bender-Zanoni
> > Great Notch, NJ
> >
> >
> > _________________________________________________________________
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> >
> >
>
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