Tandem frame fracture?

[321up]

We no longer trust our Orbit frame for long rides, there are subtle signs that it's deteriorating further but nothing conclusive that I can use to convince JD Tandems to give us a another warranty replacement.  They told us to keep an eye on it but checking it between rides might give sufficient warning for up to 300km rides but I don't have any confidence beyond that.  It's causing us too much stress and anxiety.  We can't afford to be stranded hundreds of miles from home or to fail our 600km PBP qualifier.  We have just ordered a Dolan tandem frameset as it's the only solution we can get in time. 

[rafletcher]

My attempt to scrape off an area of cracked paint on the weld between the chainstay and bottom bracket mauled the malleable metal masking any possible metal fracture. 

It may not be visible to the naked eye, but dye-pen will still show if a crack is present - it's highly unlikely that you've successfully cold welded to material together seamlessly.

[Aunt Maud]

Looks like poor quality welding to me.

It's full of bubbles and there are actually two cracks in that weld. The obvious one on the right of the stay and another fine crack (centre picture) to the left which arcs to the right around the top of the prominent vertical crack.

Any weld with bubbles in it is a bad weld.

[Ningishzidda]

Looks like poor quality welding to me.

It's full of bubbles and there are actually two cracks in that weld. The obvious one on the right of the stay and another fine crack (centre picture) to the left which arcs to the right around the top of the prominent vertical crack.

Any weld with bubbles in it is a bad weld.

[Aunt Maud]

That's nice TIG welding. It's got a regular wave pattern and no holes.

[Ningishzidda]

Is that hand or CNC?

You wouldn't believe the number of pieces that go in the skip to the Al recycling centre when they are setting up the TIG welder.

I went to Jaguar at Castle Bromwich and Land Rover at Solihull to see the Aluminium Body-in-white assembly process. Its robotic. There's a mobile crushing machine outside to reduce the size of all the 'test pieces' scrapped off during process refinement.

The guy who built OP's frame had a box of tubes and only had one shot at it.

[Aunt Maud]

To be honest, I'm not sure if it's a hand weld or not. I was using it as a comparison to the welding on the tandem, which is uneven, probably has poor penetration and is full of bubbles.

It's not unusual to see welding like that on bikes, unfortunately.  I do appreciate that it's not an easy place to weld, but he's probably paid a lot of money for a frame that has poor quality joints.

Having only one set of tubes and only one stab at it isn't a good enough reason to try and pass it off as safe, as the loads on the frame are trying to pull the weld apart at that point, it's under tension with a bit of shear thrown in for fun. It's just like a small asymmetric roof truss with a point load on it.

<thumbsdown>Bubbles</thumbsdown> 

[Ningishzidda]

IIRC, 'bubbles' in a weld pool is called 'porosity'.

The welds, although fugly, are probably safe for the loads to be encountered. They are extensive enough.

I have three Alum CNC welded frames, all nice and neat. They have much smaller beads.

Ah,, but give me brazed lugs anyday  . Even I can do them.

[Aunt Maud]

Yes, for the extra bit of weight a spigot and socket joint imight be better at that point.

I've got a couple of Cannondales that have very smooth joints and I believe the early one 1990 is hand welded, I may be wrong on that though.

That weld on the stay has failed though and 123up 321up ( even ) is right to be cheesed off.

[mrcharly-YHT]

He's brazing, not welding.

[Ningishzidda]

Maybe after some intense meditation, the braze will become a weld.

[Veloman]

IIRC, 'bubbles' in a weld pool is called 'porosity'.

The welds, although fugly, are probably safe for the loads to be encountered. They are extensive enough.

I have three Alum CNC welded frames, all nice and neat. They have much smaller beads.

Ah,, but give me brazed lugs anyday  . Even I can do them.

Porosity in a weld 'pool' is unacceptable and a source of weakness.  The 'fugly' welds are a sign of poor workmanship and any frame weld with a varying cross section of weld indicates the hand of someone who is not as skilled as they may think they are.  I would be very surprised if the weld posted by AM is anything other than automated/robotic.

And if the weld has cracked, then it is clearly not fit for purpose or safe!

[Aunt Maud]

I've seen lead welding that looks as good as that though VM. The guy who did it was a master and made it look so easy.

He did beautiful work.