Re: [CR]Bikini Lugs Cracking at the Head Tube

(Example: Production Builders:Tonard)

Date: Sun, 03 Dec 2006 14:20:15 -0500
To: <classicrendezvous@bikelist.org>
From: "John Betmanis" <johnb@oxford.net>
Subject: Re: [CR]Bikini Lugs Cracking at the Head Tube
In-Reply-To: <000d01c716fd$65d0ace0$4c7df059@049306920171>


I agree with everything Norris said.

At 05:06 PM 12/3/06 -0000, Norris Lockley wrote:
>I think Brian (apologies if it wasn't Brian) was making the point that a
>correctly and accurately mitred frame, the tubes are joined firmly by
>the brazing material at those junctures, thereby holding the tubes
>together..ie its not the lugs that hold the joints in place any more.

That may be correct. However, since the tensile strength of the braze material is half or less than that of the steel tubes, the area at the joints needs to be quite a bit greater than that available in a mitre. A bronze fillet weld does this nicely and provides stress distribution as well. Some of those "bikini lugs" just barely have the area and have a stress raiser at the edge of the lug as well. Oh, sure, they look "elegant", but the Nervex Pro style lugs with their points and scallops provide better stress distribution as well as braze area. This was explained to me by experienced cyclists over 50 years ago and is still true today.

John Betmanis
Woodstock, Ontario
Canada