Jan, My guess for the inner sleeve in the clamp section of the stem is that the sleeve creates the appropriate ID. Perhaps the clamp is bored to an oversize hole because of the lack of appropriate machinery to create a consistant, smooth and round hole. The sleeve becomes a shim. This is the only logical explanation that I can think of. My guess as to how the sleeve stays put is some sort of glue. That would be the easiest, given that the sleeve isn't under a large load. Of course, all of this is a guess.
Curt Goodrich Bicycles
607 NE 22nd Ave.
Minneapolis, MN 55418
612.788.6812
> Looking through New Cycling's Rene Herse book, and contemplating the
> Herse tandem at Il Vecchio's in Seattle, I wonder how the stems are
> made.
>
> On page 105 of the Herse book, the photos show a long bar of aluminum
> with holes drilled in strategic places. It is obvious how they will
> be cut into stems and then filed until the final shape is achieved.
>
> What puzzles me is the alloy tube inserted where the handlebars will
> go. Clearly, the aluminum bar has been filed smooth in these places,
> and an alloy tube has been inserted. This tube forms the little
> raised lip that surrounds the handlebars on every Herse stem I have
> seen (compare photo on p. 104).
>
> What puzzles me is the purpose of the tube. There is extremely little
> material above and below the tube. And since the tube will be slotted
> for the clamp, it doesn't do anything other than being a spacer - as
> if the stem was made for an oversize bar.
>
> Why not simply drill a smaller hole for the bars and do away with the
> raised lip? Also, since the inserted tube does not move, how is it
> attached? (Pressing in wouldn't work, because the perimeter is
> slotted for the clamp.) Welded in place? Bonded?
>
> Considering that Herse stems don't break, and that Herse knew what he
> was doing, and did these the same way for about 50 years, it must
> make sense. I just don't understand.
>
> Any ideas?
>
> Jan Heine, Seattle
> _______________________________________________
>
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