Originally Posted by
unterhausen
if it really is brass, good luck. If you can cut the tube and peel it off the lugs then it's a lot easier. Otherwise you have to reflow the brass and separate. Cut away the tube fairly close to the lugs but with enough material that you can still grab it with a pair of pliers. Emphasize heating the tube over heating the lug. You don't really need to get everything hot like you do when brazing -- your main goal is to get the filler to reflow. If you can get the tube slotted to the end, then it will curl away from the lug fairly easily and you can do it in stages. I have used a dremel with a cutoff saw to do that, you have to be careful not to cut the lug, but it's not the end of the world if you do.
Note that the tube may be pinned or even spot welded to the lug. You have to determine if this is the case or you'll never get it loose.
Cut the middle section out of the tube so you can look inside the joint for pins. If you see one, you can drill it out. Spot welds would be trickier to spot; you'd need to remove the paint and look for evidence of welding. Again, drill it out if you find it. The resulting holes will be filled with brass and filed smooth when you replace the tube.
Once you've determined that the tubes are free of pins or welds, drill transverse holes in the tube stubs. Arrange the frame so the tube stump is vertical, lug end up. Put a steel rod through the holes you've drilled so you can suspend a small weight from the rod. This will provide a smooth, even pull on the tube once the braze is molten. Use a large heating tip on your torch to evenly heat the lug until the braze melts. I put a pan of water underneath to catch the hot part when it comes out. A solder wick can pull out much of the braze left inside the lug while its still molten.
N.B. you will
need a fuel/oxygen setup for this; fuel/air will never get hot enough.