the parts together; they were too massive for
the Spot Welder
and too heavily mechanically loaded for soft
soldering.
A two-pronged kitchen fork broke in the joint of the handle and the fork. The thing was in use for few decades and the weld turned out to be insufficient for such long service life.
It was decided to braze the parts together; they were too massive for
the Spot Welder and too heavily mechanically loaded for soft
soldering.
The surfaces of the joint were cleaned by an abrasive wheel on a Dremel tool. The two parts were fixed together using a rig improvised from a vise, another (broken, scheduled for repairs) vise, and a clamp.
Sodium fluoroborate flux was liberally applied between and around the parts.
The sides of the joint were covered with high temperature insulation wool,
to minimize heat losses by radiation and convection.
The joint was heated with a Dremel Versaflame butane torch until visibly reddish. A silver-based filler metal (L-Ag45Sn: 45% Ag, 27% Cu, 3% Sn, 25% Zn, sol./liq. 640/680 °C, work temp. 670 °C) was then applied onto the joint from both sides and heating continued until the metal soaked well into the joint.
After cooling, the joint was thoroughly washed in hot water to remove remains of the flux, mechanically cleaned with a steel brush, then finished with an abrasive wheel.
The utensil now has a few more decades of service in its future. Eat this, capitalism!
The material took a while to heat up. Not catastrophically long, just noticeably. The filler metal wets the substrate a bit less willingly than if it'd be copper. That may be caused by not being used to the new torch (the old one bought the farm), and contaminating the flux with carbon from the flame.
There was a little too much filler metal on one side of the joint, as visible from the uneven fillet.
There is a thin groove on the back side where the two parts meet. Dirt will tend to accumulate there and will be difficult to wash out. A little drop of filler metal would take care of this, however it was not judged important enough to warrant redoing the joint. A lead-free solder could be used for filling the space without having to heat the joint to the braze melting point.
 Broken fork, detail of cleaned mating surfaces |  Holder for the fork |  Joint with flux |  Joint with flux and heat insulation |
 Joint and flame |  Joint and flame |  Fresh joint, with remains of the flux |  Repaired fork |
 Joint detail, bottom |  Joint detail, cleaned |  Joint detail, cleaned |  Joint detail, cleaned |