Originally Posted by
patmikel
I cracked my seat tube and caught it really early on thankfully. I took it to my local bike shop to get it checked out and they were able to direct me to a local aluminum welder (yay)
The local shop said that it probably cracked from riding my seat too high. I'm hoping that if I lower my seat it won't happen again. I'm curious to hear your thoughts on how aluminum reacts to welds ? Is it going to be weaker or stronger, assuming I have a good welder? This is my first post thanks.
Not sure of aluminum, but I can speak on steel.
I snapped an old road bike conversion on the downtube once. I knew a welder, and they offered to weld it back together using an oxy torch. It actually worked, and the thing rode as is for a few weeks. Later, the frame broke again not at the weld, but very close to it (taking some of the weld with it). So I just decided to buy a new one.
Heat affects metal greatly. The atoms re-arrange themselves when heated making the material either stronger or weaker depending on the temperature and how it is cooled (many metals are heat treated).
So I would take that into consideration when getting it welded. If it costs even 1/4 of the price of a new frame I would re-consider. You're also never going to be able to sell it again, or at least not for a decent price.
It could snap, or it could last and that all depends on how it's welded, what it's welded with, and how it cools. You will be changing the material structure of the frame in an area where it was supposed to be consistent. It will never be good as new again.
However, it's not THAT serious, as people braze/weld things onto their frames all of the time.
Keep in mind that my frame snapped on a very critical part of the bike that receives more stress than other areas (downtube).
If you did indeed put the seat too high, if you get it welded and get a super long seatpost, you're probably not going to put a lot of stress on the area that cracked, and that area (someone correct me if i'm wrong doesn't receive as much stress as other parts of the bike if you have a tube shoved in there well. Most of the rest of the bike will be helping with the distribution of the stress.
You're also going to be putting stress mostly not in the area where it cracked since you will be shoving the seat tube lower (but it will still receive stress).
Luckily, this repair doesn't sound like it's going to change the geometry of your frame much which is another consideration.
As always, YMMV, but I would make the price of the weld the deciding factor here. If it's anything even near $100 (which it most likely will be, as most shops have minimums usually set at 1 hr labor minimum), start looking at new frames.