Dropout Brazing

Time for fire.

The plate-style dropouts must be brazed with brass; silver solder does not have the gap-filling capabilities that brass does and will not provide a strong bond.  On the other hand, socket dropouts are designed for silver solder; in fact, many styles have small posts that you wrap the solder wire around, which then melts and flows in to the joint when heated.  Pretty simple, but I decided I needed more stress in my life.

First step - bring everything outside.  The basement does not have nearly enough ventilation for any sort of torch work, and it makes me a little nervous having an open flame near lots of natural gas appliances.  In addition, there's a smoke detector directly above my work space.

I brought the vise out with the workbench and used two 6" C-clamps to hold it down.  I opted to swap out the ratchet clamps since I did not want to melt them if I got careless.

The procedure for brass brazing has one important difference from silver soldering - flux is not added before the joint is heated.  As the torch heats the joint, the filler rod is used to wipe flux on to the joint, where it seeps in and does all the normal flux activities.  There are two different options for flux application; filler rod is often sold pre-coated with flux, or you can purchase unfluxed rod and a separate can of flux powder.  I chose the plain rod with canned powder.

To apply the flux, lightly heat the filler rod as the joint is being heated, and then dip it into the can of flux.  Once the joint starts to show a color change to dull red, literally wipe the end of the filler rod against the joint to transfer the flux.  It will then melt and take on a glassy sheen.  After the joint reaches the proper temperature, add the rod the same way you join parts with silver.

Beginning to heat the joint (the little flecks on the torch are bits of flux from the first fork blade):

The metal starts to change color and show a rainbow pattern:

Flux has been applied and the metal is turning red:

Brazing begins!  I don't have any action shots of the braze itself - a third hand would be useful to control the camera as well as the torch and the rod.  The rod is somewhat difficult to control - unused, it's about three feet long, and to prevent burning myself I need to hold it about 8-10 inches from the "hot" end.  My hands aren't incredibly steady, so it tends to wander a little as I try to apply flux or push it into the joint.  The blue on the above photo is flux that I accidentally got where I didn't want it.

One side of the dropout has been joined - the brass has flowed wherever the flux went:

Not a very pretty joint, but it gets the job done.  All of the extra material will require a lot of cleanup.  Continuing on to the other side of the dropout:

And a closeup of the finished product, in all its messy glory:

The hand torch is just barely hot enough to perform this joint, which is why there are lots of little brass blobs on the dropout; the very end of the rod would heat up enough to break off and stick to the joint, but not melt any further.  I'm pretty confident that the joint is sound, but if/when I need to rebuild the fork I'm going to go with the socket style.  This method is quite a lot of work for questionable amounts of gain.

As with the silver joints, grab a bucket of water and a stiff wire brush and clean off the excess flux.  I found the brass flux to be more difficult to remove, and ended up taking most of it off with sandpaper and the small diamond files.  It's very brittle, so you may have some success lightly tapping on it with a hammer.

Back in the shop, it's time to do the cleanup work:

I removed the excess brass with a combination of flat files, small diamond files, course emery paper, and lots of sweat.  After the joint was cleaned up, the whole thing got a thorough working over with finer grades of emery paper to clean up the roughness and present a relatively polished face for future painting.

And finally, the two completed blades side-by-side:

There are only a couple more minor operations before the whole fork is jigged up and brazed together.