By James Morikawa
This is an old picture. That frame I'm welding have "Expanding Heat Sink Sleeves" inserted into the Head-tube, and Seat-tube. Can't be seen, but there's one inserted into the Bottom-bracket.
During brazing, or welding; I use these "Heat Sinks" to keep Seat-tube, Head-tube, and Bottom-bracket distortion to a minimum. They also help prevent backside weld oxidation, and takes the place of an argon gas purge where used. Example: When tig-welding the Seat-tube/Top-tube joint (on steel frames), I only argon purge the Top-tube. The Heat Sink Sleeve protects the Seat-tube's internal surface from oxidation; no purge required there..
Below are pictures I took last night. I hope they give you an idea of how the Heat Sinks expand, and function.
The sleeve halves are fabricated from chromoly tubing, and their O.D.s' are "turned down" (lathe machined) to slightly less than the I.D. of the frame tubes they're to be used on. Internal tapers are machined on both ends. The chromoly tube is then spilt laterally (two halves).
The sleeve halves are expanded in a frame tube by a threaded pull rod, nut, and tapered collets.
On the left is how the Heat Sinks looks when the halves are mated. On the right, they're expanded in sample Headtube, and Seattube. A light expansion tension is enough, just enough to hold the sleeve in place. Torquing down too hard may distort the tool's sleeve halves.
I also have one sized for the Bottom Bracket . . . not pictured.
That's it for tonight, so "Good Night, and Good Rest" to you.