This article is from the Misc Bicycles FAQs, by various authors.
One of the people in the class is doing a fillet-brazed bike. I'll
explain a little of the difference in building and cleanup.
Fillet brazing uses no lugs at all. Tubes need to be mitered more
exactly since they will be fitted and brazed together where they meet.
The same process for jigging the frame and aligning the frame are used,
but the jigging is more exacting. I'm not sure where the brazing is
done - free brazing, in the jig, etc. During the brazing process, brass
is used to join the tubes together. With this type of fillet brazing,
lots of brass is used which provides lots to clean off and produces a
smooth curve between tubes. It looks very slick, but also takes a lot
of work to cleanup. (Dave tends to charge for this type of fillet-
brazing because of the amount of work.) Dave also does fillet-brazing
which uses much less brass. During the brazing process, he is more
careful of making sure the brass is near its final state so there is
much less cleanup, but it also doesn't provide the smooth curve between
To cleanup a fillet-brazed bike takes quite a bit of work. The person
doing it will spend 8 to 10 hours cleaning the joint areas. A carbide
bit on a grinder is used to start the process and shave away much of the
excess brass. Once a smooth begins to be established, it is lots of
sandpaper work backed up fingers to create a shape. There is some
filing, but mostly finger work. A white coat of spray paint is applied
over the areas to check for inconsistencies in the surface. The paint
will provide a better indication of what needs to be worked on than the
naked eye will.
In the end, these type of fillet-brazed bikes look really cool!