Cycling UK Forum

I found these pictures here https://yacf.co.uk/forum/index.php?topic=17.2200 whilst trawling the web for something else.





It may be old news to some, but this shows what can happen when you rely upon the lug alone to join two tubes together. The mitring of the tubes wasn't good per se but it wasn't that bad either. However the tubes were not joined except by the lug, and worse still, the lug itself wasn't joined to the head tube along the bottom. The latter fault should have been picked up during inspection and should have been quite visible when the frame had no paint on it.

This part of the frame (in frames with traditionally sized tubes) is amongst the most stressed parts. If you want to inspect frame parts for cracks, this region, the fork (especially the steerer) and the BB region are some of the favourite spots to find cracks in.

BTW had this been my frame, I might well have had it properly repaired. Failing that as a temporary measure I might have fusion welded it back together again (and kept a good eye on it subsequently). This would have a fair chance of success, since there is not much spelter to remove near the fracture line! Any such repair would have allowed the (originally unconnected) lower part of the lug and the head tube to be joined.

It is also often possible to add a gusset on the outside of lug, lap welded to it. This for sure wouldn't be your first choice for original manufacture, but as a repair it would find favour with me.

cheers

Crikey, am I glad I've got a carbon frame.

Hi,
The trouble is..........what inspection......is the modern fashion in even high tech firms today.
QA dept is non existant

QA were the bugbear of my working life back in the day of military stuff.

That's a frightening failure. Hopefully the rider had some warning before the whole lot opened up. My Raleigh Record Ace cracked in a similar area and it took me over a week to find the crack, during a week of gales I felt something just felt wobblier than normal, but put it down to the wind when inspections couldn't find anything until the crack was much bigger by the end of the week.

Didn`t you post a picture some time ago of a similar failure of one of your frames, a Pashley was it?

My only metal failures so far have been alloy seatposts. I have had 2 snap off level with the clamp top on the seat tube. Thankfully both gave way by bending over in a slow motion way, giving me time to react and bring the bike to a halt. I would hope that a steel frame would go in a similar way.

.

Brucey wrote:The latter fault should have been picked up during inspection and should have been quite visible when the frame had no paint on it.

The sad thing about this failure was that it happened shortly after a refurbishment by Mercian. If the fault would have been visable without paint, would you have expected them to pick it up?

hmm we need an X- rated thread page for stories like this - I really not old enough to see such horrors.

Applies to lugless (fillet bronze welded) too, although less likely since the tubes are more likely to be in good contact during the brazing. I had one fail at the head tube/top tube joint. I saw a fine line which left a dirty mark on my finger and knew the joint was beginning to crack. Since I could see it I could monitor its progress and it was about 4000 miles before I got it repaired. The joint had never been properly formed, no flux or brass in the junction of tubes, and the whole thing had been supported by the fillet of brazing material. It took 17 years for the first signs of cracking to appear, so I'm not grumbling.

I have had 2 lugged frames fail at the head tube/down tube joint (as in the OP photo) but mine both showed as a line along the joint of head tube to lug, almost as if the lug was separating from the joint. it is not easy to monitor the progress of a failure like that so both were repaired pretty quickly.

PH wrote:

Brucey wrote:The latter fault should have been picked up during inspection and should have been quite visible when the frame had no paint on it.

The sad thing about this failure was that it happened shortly after a refurbishment by Mercian. If the fault would have been visable without paint, would you have expected them to pick it up?

Maybe. But if you turn it on its head that would then lead you to suppose that Mercian would have some kind of responsibility for the integrity of any frame (regardless of original manufacture) that they repaint, which would be unreasonable I think. I'd argue that the bloke that did the brazing first time round should have looked and seen the lack of braze witness on the lower edge of the head lug, and then the bloke that faced the frame first time round should have spotted it perhaps... but then this frame was made in a factory as one of hundreds or thousands originally. I'm not sure that this method of construction lends itself to factory piece work...

I think this perhaps says a lot about the possible differences between mass produced frames and those that are built in smaller numbers by people who are proud of their craft and stand behind their own work.

cheers

tatanab wrote:Applies to lugless (fillet bronze welded) too, although less likely since the tubes are more likely to be in good contact during the brazing. I had one fail at the head tube/top tube joint..... The joint had never been properly formed, no flux or brass in the junction of tubes, and the whole thing had been supported by the fillet of brazing material. It took 17 years for the first signs of cracking to appear, so I'm not grumbling.

I've never been quite sure exactly what to expect with this method of construction; the spelter is nothing like so fluid as that used in a lugged joint, so perfect mitring may not give a penetrating line of braze metal between the tubes in any event. I have always supposed that, once the fillet radius gets to be so much larger than the tube wall thickness, the root of the joint is more or less shielded from the service stresses. This is pretty much how Klein and Cannondale frames were intended to work in times past.

I have had 2 lugged frames fail at the head tube/down tube joint (as in the OP photo) but mine both showed as a line along the joint of head tube to lug, almost as if the lug was separating from the joint. it is not easy to monitor the progress of a failure like that so both were repaired pretty quickly.

I've seen the same thing and IMHO this can easily happen if the joint is too hot for too long during manufacture; this can give intergranular penetration of the braze metal into the steel which results in weaker base material wherever the braze metal has been.

Mass-produced lugged Raleigh frames (form times past) often fail in this way in service (by fatigue) and the material is often obviously embrittled to some extent; the head tube will often crack in a prang, too. Here some degree of embrittlement is inevitable, since these frames were usually brazed in a molten salt bath, which is usually hotter for longer than hand brazing using a gas torch.

Silver brazing is a better method for joining lugs, but requires better fit and prep of the parts.

cheers

if this frame were put under maximum duress (big rider in the big ring blasting it uphill when out of the saddle?) then approximately how much would this area of the frame deflect from side to side? do certain tubesets also have limits of deflection as well as the standard 'hardness' and weight ratings?

the elastic limit of the frame materials is more or less implicit with the strength, since the stiffness of steel is always the same regardless of its strength.

But having said that the exact section isn't always known (weld fillet radii, tube mitring, lug manufacture etc) and nor is the strength; by the time the tubes are joined the HAZ will have made a whole spectrum of new materials near the joints, all with different strengths....

The lower head lug sees a fair bit of action from a powerful rider but AFAICT a strong rider on smooth roads is most likely to bust a typical steel frame near the BB. The lower head lug failures occur in good part because of other things; road shocks and braking forces are at least as important. The first place a frame designer saves weight is often the top tube; this leaves the down tube to do the lion's share of the work so when you go over bumps or use the brakes hard, the lower head lug sees a very high bending load indeed. Get it right and the frame can be strong enough and ride really well, Get it wrong or use it on the bumpiest roads and it can be a problem.

One route is to beef up the top tube so that it can share the bending loads better.

This means that the same poor tube prep and joining in the down tube suddenly seems to work better if the top tube is made oversized! The frameset might ride like a plank, but it is less likely to break...

cheers

I remember a clubmate's Galaxy breaking in a similar way. The down tube was short, leaving a gap at the top of the mitre that was about as big as it could be and still get covered over by the lug. We splinted it with a U-lock and a lot of cable ties and toe straps, and he rode home (Tetbury to Cheltenham) like that.