Heat Sink for Fillet Brazing

[Will Neide]

Just wondering what the general consensus is on using a heat sink when doing fillet brazing, especialy for the bottom bracket. I noticed in a few pics and videos that some people were using them and some were not using them.

[Eric Estlund]

Heat sinks are the enemy of fillet brazing heat control*.

On most bikes the BB shell is thicker and heavier then the thin tubes hitting it, and both need to be at the same temp to get good wet out for a fillet. The last thing you need is to dump more heat and for a longer duration to get the heat sink hot enough to allow the shell to get hot enough.

If one is getting a lot of distortion, or if one is having issues with temp imbalance between the tubes, the issue is in hand/ fire/ heating control, not in the need to sink it out.




*As with all things, I am sure others will disagree on the point. Yesterday I brazed up a light BB shell to a standard ish seat tube and very light stays/ DT- I could roll in the BB with no reaming needed, all sans heat sink.

[Will Neide]

Sounds good. Thanks!

[timto]

I should have read this thread before I did this very thing - HT/DT fillet with heat sink just yesterday aft. Things were wonky and I was dumping heat into the joint and not getting the results I was used to. Pulled the heat sink and all was well with the universe once more. :)

[arregui]

totally agree with Eric and been in the same situation as timto.
It seems all my distortion issues came with internal tensions in the frame (bad method of putting the front triangle together) and then releasing the beast with too much heat.

[steve garro]

NO.
- Garro.