calstar 

What's the result of over heating cast crowns, lugs and dropouts? Does it degrade the cast properties as overheating does to steel tubes?

thanks, Brian

unterhausen

My feeling is that you really can't overheat these parts without immediate failure, and that would only happen if they were under stress. Steel dropouts fail in use on occasion, but I dont' think that is due to being overheated.

I'm not really sure about overheating steel tubes either, for that matter. Usually overheating goes along with poor technique. But if you watch process videos of people that have a long record of successfully building frames, you should get an idea that it's not that easy to overheat a steel tube. But they use even heat and don't cook the tube like a beginner can.

calstar 

Thanks for the cast parts opinion. Yeah, after watching process vids it does seem those guys aren't too concerned about high temps, of course they've build 1000s of frames, so they know whats what!

Brian

Andrew R Stewart 

The biggest issue with overheating lugs and such, IMO, has little to do with resulting strength of the part but more to do with the actual brazing. Flux burn and filler separation/boil off come to mind as more frequent issues when the heat is high. Since the tubes have far less wall/mass then the junctions do I would expect overheating a crown/shell/lug/drop out will likely also see potential tubing overheating. Andy

calstar 

I'm inquiring about the cast material itself, not in relation to the inserted tubes, I should have made that clear in my original post. Primarily I'm thinking of brass brazing(would be tough to overheat much other than the flux with silver) crowns to steerers, lots of mass in the crown.

thanks, Brian

Andrew R Stewart 

Brian- Yes I thought that you were focused on the joint parts, not the tubes. Just added extra info.


I use bronze (Gasflux C-04) with their type B flux pretty much for nearly all tube to tube (with or without a socketed junction piece) these days. I do agree that one needs to get the heat up there for the filler to flow all the way in. Somewhere recently, in a forum, a poster referenced the color level, SMEX - Steel Temperature Chart , for what he saw in brass brazing. I thought his comment in another thread, https://www.bikeforums.net/framebuil...y-propane.html , about brazing temps and the color of the steel. Orange is about 1700*F and C-04 id liquid at 1620*. So expect to get the work pieces above 1620*, pretty much orange.


For those of us who started with various silver fillers this higher heat level can be daunting. Let me reassure you that many frames (as in A LOT) have seen higher temps then this during their production, without the following many failures that "should" occur if this temp level was a really bad thing. Nor does this make sense with welding, where the temps are far higher.


When I took Eisentraut's building course (1979) Al suggested that it was the differential of temps that drove many of the distortion and failures more then a small temp level above the ideal world one (for brass brazing). Si I suggest practice in maintaining a consistent and joint wide temp level that's high enough to let the brass flow in fully. Andy

calstar 

Nice concise temp chart Andy, thanks for posting it. Brian