Re: What has happened here?
Heat in the wrong place and metal tore away as you tried to remove the dropout. Nothing wrong with the tube, remember we are talking about a wall thickness of about one mm so we need to be a bit delicate when manipulating.
Re: What has happened here?
Looks like liquid metal embrittlement to me.
Re: What has happened here?
For a tabbed and slotted dropout…
If you’re doing a repair, replacement, or simply undoing a brazing task, always have the forged part in the air with the blade held at vertical. Only heat the dropout (only - remember this) until the filler material is in a liquid state. Then commit to pulling the part straight up without wiggling right, left, or sideways. Your blade broke because it was too hot, maybe under load owing to a tight slot, and your bending pattern during the pull.
It’s simple but not always easy.
Re: What has happened here?
@brewery: your post implies that the damage occured before you began to pull the dropout. Can you confirm this?
Re: What has happened here?
Using heat to bend the blade isn't odd or taboo, and didn't contribute to this situation.
Re: What has happened here?
Quote:
Originally Posted by
Mark Kelly
@
brewery: your post implies that the damage occured before you began to pull the dropout. Can you confirm this?
There was no sign of any damage to the blade before I started brazing and certainly no sign of the cracks (that I noticed) before I started to pull the dropout. I was just hypothesising as to what could possibly have caused this and thought that maybe some sort of hairline crack had formed when I slotted the blade but it sounds like it was just me making amateur mistakes while brazing.
When I pulled the dropout I was just generally heating the whole area, not just the dropout, so it sounds like I got everything a bit hot and stuffed up.
Re: What has happened here?
Quote:
Originally Posted by
brewery
There was no sign of any damage to the blade before I started brazing and certainly no sign of the cracks (that I noticed) before I started to pull the dropout. I was just hypothesising as to what could possibly have caused this and thought that maybe some sort of hairline crack had formed when I slotted the blade but it sounds like it was just me making amateur mistakes while brazing.
When I pulled the dropout I was just generally heating the whole area, not just the dropout, so it sounds like I got everything a bit hot and stuffed up.
Never (ever) heat the blade. Heat the forged or cast part and it will bring the blade up to temp.