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5.14 Frame Building Part 4


This article is from the Misc Bicycles FAQs, by various authors.

5.14 Frame Building Part 4

From: terryz@microsoft.com (Terry Zmrhal)

This fourth class would keep everyone busy with various aspects of
finishing up the bike. We would begin with cleanup on the seatstays,
similar to what was done with the chainstays, and cleanup around the
bottom bracket and top of the seatstays. A little more cleanup around
the areas where braze-ons would go, the brazing of the braze-ons,
filling the vent holes, and cleanup of the braze-ons.

Rear Triangle Cleanup
One of the last things that was done during the third class was brazing
the rear triangle together. Three areas needed to be cleaned up - the
chainstay/bottom bracket junction, seatstay/dropout junction, and
seatstay/seat tube junction. The cleanup around the chainstay/bottom
bracket junction was similar to clean up around any other lug - use
file-backed sandpaper to clean the tubes, small files to finish the lug
edges, and then file or thumb backed sandpaper on the lug itself. This
actually took longer than it sounds because of the tight and small
spaces around the bottom bracket. It took some maneuvering of various
files to get every place that needed to be cleaned.

At the seatstay/dropout junction, it was necessary to cleanup the ends
of the seatstays similar to what was done with the chainstays. This was
to provide a half-round smooth curve between the stay and dropout and
then to provide smooth lines on the top and bottom of the dropout where
the tabs would stick out. The outside of the stay would have a
pronounced curve, while the inside would have a very small curve since
most of the stay sits outside of the dropout to allow for more clearance
of chain and cogs. To create this curve we used the hand-held air-
powered belt sander as before just down to the point where the metal of
the dropout was showing. The curve here was cut parallel to the
chainstay on the outside, versus perpendicular to the seatstay itself.
The only difference is aesthetics. On the inside it was cut
perpendicular to the seatstay because there wasn't much to curve. It
was suggested that the inside and outside curves be done first so that
the curves or edges of the tabs could be defined according to how these
curves looked. The bottom had just a small portion of the dropout tab
showing so that was smoothed out using files and sandpaper. On the top,
there was a definite edge on the outside, less on the inside, so I
defined an edge on the outside.

Cleaning the seatstay/seat tube junction was again fairly easy other
than getting into tight spots. Dave had done a very good job of using
only as much silver as necessary which meant very little cleanup. The
tops were easy to sand with file-backed sandpaper. The underside
required some small round files.


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