Next project, looking for pointers ahead of time

[mcdanida]

Aluminum frames are built stiffer because aluminum has no stress tolerance before cyclic fatigue occurs. So by making the frame stiffer, the less its affected by alternating stress.

Steel is going to absorb the bumps better due to its higher elasticity (ability to spring back). Aluminum under stress either causes fatigue (stress over time eventually ending in breaking, cracking) or plastic deformation (being permanantly mis-shapen).

That's why you see larger diameter aluminum tubes because its stiffer. Some bike frames are put together under tension as well to increase rigidity. Frame geometry is important too for comfort.

But for the average rider/hobbyist I'd say you could only go wrong by pairing an aluminum frame with aluminum mag wheels and having no suspension and while riding on rough roads.

Just pick whatever frame looks cool .

In my case as rookies, whatever is cheap.

 

[LewieBike]

Cheaper aluminum frames. I've seen so many that had cracks on the head tubes from trail riding. Once the bearing area of the head tube starts a crack that frame is dead. Steel has less chance of cyclic fatigue like other poster's have mentioned.

 

[Sidewinder Jerry]

In my case as rookies, whatever is cheap.

Though the Schwinn Sidewinder cost around $200+, its worth the investment. Still a work in progress but here's my Sidewinder featuring a triple chainring shift kit. Had to cover up the white wheel reflectors.

 

[darwin]

If I have a crack in an aluminum frame I'll s**t can it. Nothing is worth a tumble at 30mph. It's really an alloy and not just beer cans. I don't know how strong a heliarc weld would hold up using just aluminum as a filler or if it should be done.

 

[Sidewinder Jerry]

If I have a crack in an aluminum frame I'll sh*t can it. Nothing is worth a tumble at 30mph. It's really an alloy and not just beer cans. I don't know how strong a heliarc weld would hold up using just aluminum as a filler or if it should be done.

I've always heard aluminum should be tig weld if a strong weld is required

 

[LewieBike]

If I have a crack in an aluminum frame I'll sh*t can it. Nothing is worth a tumble at 30mph. It's really an alloy and not just beer cans. I don't know how strong a heliarc weld would hold up using just aluminum as a filler or if it should be done.

There's a thing about the material and whether it will need a heat treatment after the repair, Something, something about 6000 grade versus 7000 grade aluminum.

When I was at Burly we had a few weeks while the old tandem line was idled while the Bike Friday's weld jigs and tooling were being prototyped and we had one of the owners build (overnight no less..) a folding 20" wheel SWB recumbent based on the Bike Friday tooling, that needed a frame for the mesh fabric seat. And they welded up an aluminum tubing seat frame and didn't heat treat it, and it cracked after about 5 days of use.

 

[LewieBike]

I've always heard aluminum should be tig weld if a strong weld is required

Gary Hale's recumbent seat frames were made from aluminum tubes fitted with reinforcement aluminum plugs placed at the cross pieces locations, glued in with green shaft-locker LocTite.

 

[Wrench]

Yea, that's the thing about welding a crack on an aluminum bike frame. The aluminum next to the weld becomes weak unlike steel

Properly Welding a crack on an aluminum bike frame is more involved than one might think.
Their are different methods for different areas of the bike frame and annealing is important
A sleeve or tag can be welded over the crack or a pipe insert is used in the tubing, Rarely is the crack just welded up solo with no reinforcement.

These same methods are used to repair Steel bike frames.

 

[LewieBike]

Yea, that's the thing about welding a crack on an aluminum bike frame. The aluminum next to the weld becomes weak unlike steel

Properly Welding a crack on an aluminum bike frame is more involved than one might think.
Their are different methods for different areas of the bike frame and annealing is important
A sleeve or tag can be welded over the crack or a pipe insert is used in the tubing, Rarely is the crack just welded up solo with no reinforcement.

These same methods are used to repair Steel bike frames.

Depends on the alloy of steel, certain Chrome Manganese Molybdenum bike frame tubes like Reynolds are alloyed so the heat of brazing strengthens the heat affected area. That's why Reynolds was popular with hand built fillet brazed MTB builders like Moots, Mountain Goat and Ritchey.

 

[Wrench]

Yes welding techniques of different metals is very important