Grigg,
I have a question about your technique. Why doesn't the bolt fuse or weld to the surrounding material when you tack weld on to it? Does that ever happen?
The trick is to avoid that, which isn't hard. If the heat is concentrated on the screw or bolt that is what melts and what you add your filler metal to it. If the arc wanders off to the larger part then yes, you can weld the two together.
Large bolts you can do this with a stick welder or MIG. Some
Specialty Rods for Stick welding
Smaller you can try MIG in short pulses. Place a washer over the end to use as a shield to avoid welding the surrounding metal.
All sizes, and particularly tiny screws, TIG welding gives the control and accuracy necessary, both the adjustable amps on the fly, and pin point precision.
TIG also allows you to reach down in a hole, even bolts broken off well below the surface can be extracted.
Sometimes I keep the arc on the part well after I've built up the metal I need to grab, further heating the screw/bolt.
Sounds counter intuitive, hot bolt expands so wouldn't it be harder to remove?? except I think expanding crushes the rust or otherwise makes room and brakes free, right away it shrinks back some making a little room to move.
The concentrated heat on the screw also brakes free Loctite without having to heat the entire part, if that's a factor.
If it doesn't work on the first try, try again, and again after that, the more heat cycles help.
Grigg
