Cracked head tube

[Chris Jeggo]

...
I made a living that exceeded my paper round brazing up the broken chain stays on Raleigh choppers, admittedly, I didnt pass on my secret of slugging the tube together and running a line of braze round it, as any one could do that, rather than give me 2 pounds

I don't understand "slugging the tube together". What exactly do you mean?
Chris

[jo' bo]

...
I made a living that exceeded my paper round brazing up the broken chain stays on Raleigh choppers, admittedly, I didnt pass on my secret of slugging the tube together and running a line of braze round it, as any one could do that, rather than give me 2 pounds

I don't understand "slugging the tube together". What exactly do you mean?
Chris

Stick a "slug" of steel bar as an interference fit in to the broken tubes ,hammer them back together so they meet, then run a line of braze round them

I got into a heated debate with my friends dad over it

Youl never braze that so it holds he said

Yes I will I replied, returned the next day looking smug for my money

He pulled it, kicked then stamped on it repeatedly till he had to accept I had indeed "brazed "it so it held

Dont know how you've,done that he said, before reluctantly handing over my money, he was still knocking at it with a hammer as I left

[Chris Jeggo]

Thanks, jo' bo, for explaining that.

Chris

[KTHSullivan]

Here’s a curious case - how do you get a crack like this? It’s a mid ‘80s Record Ace. Running into something solid is the usual explanation...

https://www.ebay.co.uk/itm/373580999210

F85933E0-59A6-45EC-91C5-03082AFF9E90.jpeg

Looking at the photo it appears that there is some "grain" visible on the section of the crack ( I have zoomed in and that's my perception). If so I would hazard a guess that during the initial braze up of the joint it was cooled too rapidly. 531 tubing has a Carbon content of 0.35% and effectively the same heat treatment characteristics of the old EN16 grade steels. As a consequence it would lend itself quite readily to hardening, be it accidently or on purpose. The caveat obviously being that the head tube is indeed BS970 and not a drain pipe offcut the builder may have had to hand. A carburizing flame may have also induced a degree of local surface hardening, or there may have been an inclusion within the metal that may have acted as a seed for crack propagation. Perhaps the frame in question was brazed by an apprentice. But more likely I tend to agree with the OP; it's probably been run into something immovable.

[531colin]

Steel forks traditionally are curved, and framebuilders have traditionally bent this curve round a former to give different fork offsets.
Yet this head tube is supposed to have cracked due to a front impact.
Tell me how this works please?
The fork blades are malleable enough to be formed, but the head tube (same material) is brittle and cracks when overloaded.

[rogerzilla]

It's dead, Jim.

[scottg]

It's dead, Jim.

I've render the horse down to the fats, made & sold enough soap, to buy something new
at Spa in the time this thread has been running.

[markjohnobrien]

Here’s a curious case - how do you get a crack like this? It’s a mid ‘80s Record Ace. Running into something solid is the usual explanation...

https://www.ebay.co.uk/itm/373580999210

F85933E0-59A6-45EC-91C5-03082AFF9E90.jpeg

Looks to me like it’s run into something - as is normally the case.

[KTHSullivan]

Steel forks traditionally are curved, and framebuilders have traditionally bent this curve round a former to give different fork offsets.
Yet this head tube is supposed to have cracked due to a front impact.
Tell me how this works please?
The fork blades are malleable enough to be formed, but the head tube (same material) is brittle and cracks when overloaded.

Colin might be endeavouring to teach Granny to suck eggs but here goes.

A reasonable analogy would be an engineers file. Before heat treatment the crystalline structure is uniform throughout the entire artefact, after heat treatment the tang is soft enough to be bent with the judicious use of a hammer; but try it on the business end and it would shatter. So we have the same initial material that demonstrates different characteristics dependent upon what heating/cooling regime it has been subject to.

Getting back to the problem at hand I see the following as a possible explanation of the above scenario. The head tube assembly may have been subject to inadvertent heat treatment that hardened it reducing it's toughness and subsequent ability to withstand shock loading. The fork assembly has been manufactured correctly and subsequently is operating within the design "region of proportionality" (elastic limit) of the material. The forks are obviously attached to the head tube on a loading basis. The forks are subject to load during use, some of which in turn is transmitted to the headtube assembly. This applied force is now impinging on a component that is no longer operating within it's material design parameters and fails.

Best I can come up with.

K

[KTHSullivan]

Steel forks traditionally are curved, and framebuilders have traditionally bent this curve round a former to give different fork offsets.
Yet this head tube is supposed to have cracked due to a front impact.
Tell me how this works please?
The fork blades are malleable enough to be formed, but the head tube (same material) is brittle and cracks when overloaded.

Double post.

[alexnharvey]

It's dead, Jim.

Was that ever questioned?

What was originally asked is how does such a crack occur. If you're not interested in discussing it just walk on by.

I'm so sorry, I hadn't realised you were the forum police and that jokes weren't allowed.

Well, now you know. or maybe you just need to work on better jokes?

A few times recently we have had some posters try to make posts and queries of technical interest that some have taken as purely practical questions of can and should it be fixed rather than how did it happen and what does it mean. I think that is an unfortunate change in the culture.

[alexnharvey]

Steel forks traditionally are curved, and framebuilders have traditionally bent this curve round a former to give different fork offsets.
Yet this head tube is supposed to have cracked due to a front impact.
Tell me how this works please?
The fork blades are malleable enough to be formed, but the head tube (same material) is brittle and cracks when overloaded.

Colin might be endeavouring to teach Granny to suck eggs but here goes.

A reasonable analogy would be an engineers file. Before heat treatment the crystalline structure is uniform throughout the entire artefact, after heat treatment the tang is soft enough to be bent with the judicious use of a hammer; but try it on the business end and it would shatter. So we have the same initial material that demonstrates different characteristics dependent upon what heating/cooling regime it has been subject to.

Getting back to the problem at hand I see the following as a possible explanation of the above scenario. The head tube assembly may have been subject to inadvertent heat treatment that hardened it reducing it's toughness and subsequent ability to withstand shock loading. The fork assembly has been manufactured correctly and subsequently is operating within the design "region of proportionality" (elastic limit) of the material. The forks are obviously attached to the head tube on a loading basis. The forks are subject to load during use, some of which in turn is transmitted to the headtube assembly. This applied force is now impinging on a component that is no longer operating within it's material design parameters and fails.

Best I can come up with.

K

It's a good effort but that is a fatigue crack all day long.

[531colin]

Occam's razor says something like "if there are 2 competing explanations for an observation, then the explanation which requires the fewest assumptions is likely to be right."
So if this crack is due to a front shunt, we have to assume that the apprentice over-heated the tube and made it brittle; 531 wasn't known for this, but 753 was. We have to further assume that there was sufficient force to crack the tube, but insufficient force to bend the un-cracked bit of the tube, because the cracked tube is hardly out of alignment at all.
On the other hand, the crack follows an obvious stress-raiser (the lug) for most of its length, before branching off, and you don't expect fatigue cracks to be displaced until the tube is almost completely failed.

[David9694]

Not worth worrying about.
The frame itself is pretty average; just the 3 main tubes 531, plain gauge.
Head tube is un-specified (ie cheap) tubing; an artisan framebuilder would have filed the lugs thinner at the ends to reduce the stress-raiser, and probably used a better lugset in the first place.
On the other hand, if you were looking for excitement, you could probably sleeve it internally and silver solder it up; the crack only goes part way round. As above, though, the head tube needs to be straight(ish) when finished.

Whilst I would agree that it's probably not worth repairing I'm pretty sure that those Record Aces were built with a full 531C tube set. I had the opportunity to buy a lot of them from Raleigh at a good price when they cleared them out, selling them on at £200 if I remember correctly.

1982-85 models in Forest green or Ice Green were 531 throughout. This one, that followed, is forks and main tubes only.

[iandusud]

Not worth worrying about.
The frame itself is pretty average; just the 3 main tubes 531, plain gauge.
Head tube is un-specified (ie cheap) tubing; an artisan framebuilder would have filed the lugs thinner at the ends to reduce the stress-raiser, and probably used a better lugset in the first place.
On the other hand, if you were looking for excitement, you could probably sleeve it internally and silver solder it up; the crack only goes part way round. As above, though, the head tube needs to be straight(ish) when finished.

Whilst I would agree that it's probably not worth repairing I'm pretty sure that those Record Aces were built with a full 531C tube set. I had the opportunity to buy a lot of them from Raleigh at a good price when they cleared them out, selling them on at £200 if I remember correctly.

1982-85 models in Forest green or Ice Green were 531 throughout. This one, that followed, is forks and main tubes only.

Thank you for the clarification. It was a long time ago!