Thread on buckled head tube?
04-02-16 | 10:28 AM
#1
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From: Southern Ontario
Thread on buckled head tube?
I can't remember if it was here or bicycle mechanics or framebuilding but there was some discussion about a couple of bikes with buckled head tubes but not from a crash. It was a ring like the headtube was compressing.
I just ran across this blog where a guy fixed a frame like this.
cyclops: Heat tube repair
He says:
The construction was weird. The HT part of the lugs were brazed with Copper, the other sections with Nickel-Silver. From what I gathered online, Copper filler is used in factories; the lugs are first brazed on the HT as a sub-assembly in a furnace or hearth and the rest is brazed later. Probably in a hearth or furnace again, since Copper melts at a considerably higher temperature than brass or Nickel-Silver.
And then it got weirder. The head tube was made of some weird alloy... It didn't feel particularly soft under the saw, but under the torch it felt nothing like cromoly steel. It heated up quickly, and it started melting on me!!
Who knows what that thing was made of... some sort of machinable iron?? Or maybe the high heat of the Copper brazing furnace messed up the steel. At any rate, the poor material is likely the reason the tube buckled.
I just ran across this blog where a guy fixed a frame like this.
cyclops: Heat tube repair
He says:
The construction was weird. The HT part of the lugs were brazed with Copper, the other sections with Nickel-Silver. From what I gathered online, Copper filler is used in factories; the lugs are first brazed on the HT as a sub-assembly in a furnace or hearth and the rest is brazed later. Probably in a hearth or furnace again, since Copper melts at a considerably higher temperature than brass or Nickel-Silver.
And then it got weirder. The head tube was made of some weird alloy... It didn't feel particularly soft under the saw, but under the torch it felt nothing like cromoly steel. It heated up quickly, and it started melting on me!!
Who knows what that thing was made of... some sort of machinable iron?? Or maybe the high heat of the Copper brazing furnace messed up the steel. At any rate, the poor material is likely the reason the tube buckled.
04-02-16 | 12:00 PM
#2
Senior Member
Joined: Jul 2009
Posts: 11,128
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Bikes: 1986 Alan Record Carbonio, 1985 Vitus Plus Carbone 7, 1984 Peugeot PSV, 1972 Line Seeker, 1986(est.) Medici Aerodynamic (Project), 1985(est.) Peugeot PY10FC
The bump on his head tube looked exactly like the one that appeared on my defective Peugeot PSV that I returned to the dealer after only a couple of weeks owning it.....
I think it's either a heat treating or brazing overheating caused defect....
Only proper fix is replacement as was done on that video......
I think it's either a heat treating or brazing overheating caused defect....
Only proper fix is replacement as was done on that video......
