It can be difficult to judge just how well a lugged steel frame is built. The average cyclist probably has a hard time seeing the difference in quality between a top custom frame and a good production frame. There are those who think that a production frame from Toyo, Colnogo, Waterford, or Maxway is virtually as well made, if not as well painted, as hand built frame by Peter Weigle, Johnny Coast, Richard Sachs, or any number of top custom builders. But if we look below the paint we'll soon find a lot that distinguishes good custom frames from even the best off-the-shelf frames.
Among the things that distinguish the best frames is preparation of the lugs, careful selection and mitering of the tubes, good brazing techniques, and near perfect alignment. Let's take a look at some of the details of a top quality frame:
One of the things that's easy to spot and that distinguishes a production frame from a fine custom frame is the way the lugs are finished. As one of our regular readers put it when I asked about one of his American production frame, "It's never been in the same room as a file."
A good custom builder files, shapes, and thins the lugs. Of course this is done not only for aesthetic reasons. The edges of lugs form stress risers. These are areas where a tube is most likely to fail do to the sudden transition from a stiff area to a flexible one. From Wikipedia:
"Geometric discontinuities cause an object to experience a local increase in the intensity of a stress field. The examples of shapes that cause these concentrations are: cracks, sharp corners, holes and, changes in the cross-sectional area of the object. High local stresses can cause the object to fail more quickly than if it wasn't there. Engineers must design the geometry to minimize stress concentrations."
By thinning a lugs points the builders is able to make a more gradual transition and lessen the stress riser. But filing lugs is done by hand and takes a great deal of time. This is time the production builder can't afford. Besides, the frame probably won't crack if you don't file the lugs.
Likewise you'll notice that some points under the tubes of custom frames are, in fact, not pointed. Rather the builder has rounded them to minimize what is sometimes called the "can opener effect". The frame probably won't fail if those points are not rounded, but then again, why take the chance.
Thinning lugs also saves a little weight. It may not be much, but little details do add up. And finally, thinned lugs look a lot better. They show that the builder really cared. So next time someone tells you their production frame is as good as a custom, look at the lugs.
In future posts I'll write about tube selection, mitering, alignment, and brazing.
30 January, 2007
Posted by Velo Orange at 4:27:00 PM