Adding gusset to Ali bike frame

[Mid Wales welder]

Hello all!

I have a mountain bike frame that has a crack in it (at the toe of the weld where the pen is pointing) which I'm going to weld up. Then Im going to add a gusset on each side to strengthen it a bit. The frame is 6061 T6 Ali, the gusset will be out of the same material and I will use 5356 filler, using a Lincoln V205t AC/DC inverter. I'll post picks when I'm done.
Just wondering if anyone can invisage any problems with this?

 

[Richard.]

Well although the 5356 filler is a stronger weld I'd probably do the job with 4043. As it's a bit more ductile and less crack sensitive. I don't really see any issues. Though unless there is a reason why a gusset shouldn't be there (obstruction for example) but I'm sure you've already checked that.

 

[Rocketman]

You will loose the T6 heat treatment and hence make the ali weaker, on the other hand you are adding extra strength. Will the two equal each other out is anyone's guess.

 

[Mid Wales welder]

Not sure if I have any 4043 but if I do I will use that, thanks for the tip.
Yeh I thought about loosing the T6 but there's not much I can do about that as I have to weld the crack otherwise the frame may as well go in the skip, hoping the gussets will help with that though! Thanks for the comments!

 

[Richard.]

Not sure if I have any 4043 but if I do I will use that, thanks for the tip.
Yeh I thought about loosing the T6 but there's not much I can do about that as I have to weld the crack otherwise the frame may as well go in the skip, hoping the gussets will help with that though! Thanks for the comments!

I think you'll be ok. Those gussets will more than replace any strength lost by adding heat to the material. Just keep the heat to a minimum. There is no need to fully weld them in, a couple small stitches top and bottom of the gusset will be plenty.

 

[Rocketman]

Not sure if I have any 4043 but if I do I will use that, thanks for the tip.
Yeh I thought about loosing the T6 but there's not much I can do about that as I have to weld the crack otherwise the frame may as well go in the skip, hoping the gussets will help with that though! Thanks for the comments!

You can get t6 redone but I would guess it isn't worth the cost hassle to the point of getting a second-hand frame that doesn't need repairing would be easier and cheaper.

 

[Leetig]

First week after I got my tig rig I got asked to do the very same repair. I turned it down as I wasn't confident in doing it. Anyway a few days after he got repair done it had been migged and looked like a pigeon had **** all over it!!!
Point is that it hasn't cracked since after nearly a year of abuse without any gussets so I think you will be fine.

MOD: language edit

 

[outofthefire]

Why did it crack in the first place? if its due to flex in the frame you'll probably find that if you strengthen it there it'll crack somewhere else.

 

[Mid Wales welder]

First week after I got my tig rig I got asked to do the very same repair. I turned it down as I wasn't confident in doing it. Anyway a few days after he got repair done it had been migged and looked like a pigeon had **** all over it!!!
Point is that it hasn't cracked since after nearly a year of abuse without any gussets so I think you will be fine.

MOD: language edit

That sounds promising then, thanks!

 

[Mid Wales welder]

Why did it crack in the first place? if its due to flex in the frame you'll probably find that if you strengthen it there it'll crack somewhere else.

I'm not sure how it has cracked as it's not my frame, it's defin had some abuse as it's been ridden in downhill races! This is just a prototype frame apparently and the production model frame has the gusset in now as standard.

 

[Mid Wales welder]

I think you'll be ok. Those gussets will more than replace any strength lost by adding heat to the material. Just keep the heat to a minimum. There is no need to fully weld them in, a couple small stitches top and bottom of the gusset will be plenty.

The gussets are only going to be 2inchs max on each side of the triangle as it were so would it be ok to fully weld but just do one side then let it cool and then do the other?

MOD? sorry for three posts, don't know how to put three quotes in one reply lol

 

[Leetig]

Why did it crack in the first place? if its due to flex in the frame you'll probably find that if you strengthen it there it'll crack somewhere else.

I've been told that the ally framed bikes are renowned for cracking. So a lot go for a carbon frame.

 

[Mid Wales welder]

I've been told that the ally framed bikes are renowned for cracking. So a lot go for a carbon frame.

Why is that do you think? If it goes again then he will get a new frame, I'll mention to him about a carbon one, something like 4140 chromoly maybe?

 

[Mid Wales welder]

I'll be using a foot pedal, squarewave, about 65 EN on the balance and about 200 on the frequency.

 

[HMB]

I've been told that the ally framed bikes are renowned for cracking. So a lot go for a carbon frame.

My orange sub zero is Ali. That ain't cracked

 

[Leetig]

I know nothing about them but my mate is cycling mad and competes at a high level. Don't want to start a debate lol

 

[antonio costa]

Mid wales welder, like sugested above if you're really decided to weld it keep the heat imput low and like Richard said just do a few stitches around the reinforcement gusset.
Anyway the t6 heat treatment will be gone on that area and what worries me most is that the crack is in what looks like an high stress area and downhill bikes take an hell of a beating.
If it was a road or cross country bike I would have no problems welding it but a freeride or downhill bike I probably would refuse the work

 

[Rocketman]

Well..................... All ali bikes will crack eventually regardless of what you use it for - ali by it's very nature will always fail were as steel used within it's limits with no corrosion could last literally forever. BUT and it's a big BUT a correctly design aluminium frame will last a hell of a long time.

And further to the point if you have been into cycling for a long period you will know just how steel frames are prone to failure. Had it on several steel frame bikes over the years myself.

As far as carbon fibre bike go they are probably even more prone to failure than aluminium.


Looking at this as Antonio says if that's a true down hill racer which is being used seriously I wouldn't dare weld it up.

 

[Mid Wales welder]

Well, I told the lad about the risks of welding it and he was happy to just go ahead with it as the frame will just go in the bin otherwise anyway so may as well give it a go, he also wanted it fully welded. I used 4043 filler, foot pedal, 65EN on the balance and 150 on frequency, wire brushed and then wiped with acetone. Welded ok, just a little awkward to get in a few places and didn't come out quite as neat as I wanted but hopefully it will do the job! I don't often do much tig welding and very rarely do Ali! This frame was a prototype, the new production frame has the guesses in as standard.

 

[Richard.]

That's a really nice job.