What an ugly crack

[techguy]

OK thats cool, but I have seen frames crack becuase the headset cups have been hammered in between two planks of wood and nowhere near a weld...

[dirtrider]

The External crack happened first allowing the cup to flex and hence crack' date=' Normally this will happen when the cups are not?pressed in straight and it ovalises the frame createing a stress riser...[/quote']

 

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Once a cup is all the way in it is straight.

 

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I can't see how ovalisation causes a stress riser. You need a sharp point, not a gentle curve for that.

 

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Frame ovalisation at the headset is a different issue not associated with cracks.

 

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Think weld...think manufacturing steps.

 

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Is it a fact that once the cup is in "all" the way that it is seated properly ? I think not . BTW it is not that difficult to get the wrong size in there either .

[Tieffels]

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JB, seems you have it figured out?

I'm guessing the external crack propagated along the heat affected zone (HAZ) adjacent to the weld.. This might indicate that the frame was not heat treated properly. My money is also on the cup having cracked first, not sure why thought, forcing the tear in the head tube as stated above along the HAZ.. 

 

So my question to you is what does the (most) correct guess win? 

[Guest Big H]

You didn't do to well in trying to hide the brand there.

 

ok' date=' i give up?what brand is it?

[/quote']

 

..... most likely a Raleigh!!!!!!

[Johan Bornman]

Is it a fact that once the cup is in "all" the way that it is seated properly ? I think not . BTW it is not that difficult to get the wrong size in there either .

 

Well, maybe you and I have a different interpretationof "seated properly."

 

My version looks like this.

 

1) Cup is right size and needs to be press-fit into the flared flange.

2) Flared flange is perfectly perpendicular to the axis of the head tube. In other words, the outer rim is reamed so that we don't have a 91-degree angle somewhere.

2) Cup is perfectly proportioned and not higher on one side than the other.

3) The cup's seating depth is significant - i.e. not 0.5mm or something like that. It has a depth that will prevent it from turning sideways in the right-sized recess.

4) The recess is perfectly round and square to the axis of the head tube.

5) The fitted cup is exactly flush with all edges of the flange.

6) The cup cannot move any deeper and is dead flush with the inner stop in the flange.

 

That is "seated properly".  Under those conditions I cannot see how it can be in skew.

 

Wrong size? I don't think so. These things go up in large increments and moering one in there that is 2mm bigger in dia is impossible unless you are a blacksmith and your forge is hot.

 

 

Johan Bornman2010-02-17 07:10:18

[Pappa Bear]

My Guess......

 

When the flanges was welded to the head tube it was done incorrectly (at that spot - wheer the crack started).  I guess to much heat - due to "over welding" or the weld not done completely.  The excess weld was then machined of / lack of weld was then covered under the paint.  The crack then started at the poor welding spot due to forward and aft vibrations.......  The frame cracked and then the headset cup...

 

Or the headset cup cracked first due to poor quality / manufacturing / was the fork perhaps jammed and then force to turn - thus "opening" the cups and then cracking the frame at the above mentioned bad spot?

[Johan Bornman]

<?: prefix = o ns = "urn:schemas-microsoft-com:office:office" />

JB, seems you have it figured out?

I'm guessing the external crack propagated along the heat affected zone (HAZ) adjacent to the weld.. This might indicate that the frame was not heat treated properly. My money is also on the cup having cracked first, not sure why thought, forcing the tear in the head tube as stated above along the HAZ.. 

 

So my question to you is what does the (most) correct guess win? 

[/quote']

 

No, I don't have it figured out. I have an idea but it is only guesswork at this stage.

 

I agree with the heat affected zone thing. The crack is definitely along that line. My guess was also a heat treatment problem but my engineering prof friend phoned me (he's too shy to post, he just lurks) and recons the frame was TIG-welded instead of flame-welded.

 

He says the TIG-welding process creates a large temperature difference between the two items to be welded (in this case a small flange on a large heat-sapping tube) and creates stresses that cannot be removed by mere heat treatment afterwards. I think thats an accurate (60% or so) rendition of what he said.

 

Where's Lefty, GreatWhite, Edman and the gang?

[dirtrider]

ok Johan You have made your point !!! Now that we have found out the the cup was installed by a qualified rocket scientist we can eliminate a faulty installation as being the problem .

 

 

 

I know you most probably do above steps to install all your bearings , was just wondering how many other people follow the correct procedure ?

 

Would you like me to show you how to get an oversize bearing into ANY frame with my hydrolic press ?

[Johan Bornman]

ok Johan You have made your point !!! Now that we have found out the the cup was installed by a qualified rocket scientist we can eliminate a faulty installation as being the problem .

I know you most probably do above steps to install all your bearings ' date=' was just wondering how many other people follow the correct procedure ?
Would you like me to show you how to get an oversize bearing into ANY frame with my hydrolic press ?[/quote']

 

Yup, I follow the correct steps as above. Yet I still use two planks from time to time. I see that method is dissed here somewhere. I better keep quiet.

 

I don't believe installation was the problem but I still don't know if the inner race thing broke first or the frame broke first. Both scenarios could lead to the other also cracking.

 

The question I haven't asked yet: Is this a gaurantee replacement candidate?

 

 

[Minion]

Why would the headset cup crack? Aren't they normally in compression from the press fit and normal loading?

[Pappa Bear]

what about a loose headset.....resulting in excessive movment - vibration with large amplitudes........ resulting in the crack forming in he weakest point of the headtube?.........  Still think the cup went before the frame. 

[HeartCoppi]

JB, help me out, because I'm not clear regarding the construction of the head tube.

 

I assume you've taken out the cup to study the construction of the head tube.

 

The second picture shows the inside of the aluminium tube with some relatively clean grease. But I cant see a weld root or discoloration that would be evident from a properly penetrated weld. This could have been removed by post weld machining though(or reaming or grinding).

 

From a manufacturing perspective it seems really complex. to weld. Mainly because it involves so much preparation and post weld production steps including inspection and testing (eg ultrasound or Xray). Exceptional material cleanliness is one key to success and requires discipline and process. This is all extra cost to a manufacturer. Think of all the possibilities and the steps required; and the capital investment required before you even strike an arc on the first tube.

 

Three options you haven't clarified pertaining to how it is welded:

 

(1) cup flange is slid over the tube. TIG PULSE AC/DC overlap weld. Geometrically difficult to smooth the radius in to one; with or without filler.

 

(2) tube is undercut, cup flange is slid over undercut section and butts against shoulder. TIG Pulse AC/DC butt weld with filler is easy to locate and machine the radius flow.

 

(3) straight butt TIG pulse AC/DC with filler would be most jig intensive with through form root.

 

 

 

But why?

 

Aluminium is such a malleable material. It can be easily spun out or bellowed by press forming. Then an additional tube can be inserted through the tube. This can be fixed in several ways and adds some addition strength. Its cut to critical length to serve as stopper for the head set cup. Simpler and more economical assembly line.

 

In theory.

 

Sorry if I've missed something but I need a personal visual. What do you think?

 

 

 

 

 

cont'd

[HeartCoppi]

I assume that this is how the frame was assembled.

 

I ask this because I cant see any degassing apertures for the weld attachment of the down tube and top tube to the head tube. They may now be covered by the reinforcing tube.

 

cont'd

 

 

 

The horizontal crack is then answered by your answer as to the assembly.

 

If the cup flanges were welded on, then chickenrun4me and pappa bear and pal prof have some sound contributions. But not entirely. Its clearly related to the HAZ and the quality of post weld HT.

 

But generally: (a) the material is very thin; depending on the weld prep as I detailed above, there may be no wall thickness variation; (b) weld filler metal diameter cools the weld pool; © and my bet that such an esteemed company would be semi if not fully automated to ensure optimal repeatability and quality. (d)As for heat sinking I am not sure as to the jig construction and its influence on heat flow, but it may well balance the equation.

 

 

 

It the head tube flange is formed and stiffened then the horizontal crack simply follows a forming line or the last section of single walling before strengthened by double tubing.

 

 

 

What do you think?

 

 

 

 

 

cont'd

 

 

 

 

 

 

 

In my opinion this crack originated from the head set cup and specifically from the inside diameter of the headset cup.

 

Why?

 

Simple maths: the ID is the smaller circumference. and the OD the larger circumference.

 

The race material has a yield strength and elongation value indicative of the point of gross failure. The race is hardened material and is inherently stressed in comparison to ferritic material.

 

Express this as a percentage of the circumference and the smaller ID has the least units required in expansion to express a failure. The crack then exists and simply propagates outward along the stress vector. Eventually the head tube flange will also fail. This is the vertical tear. The aluminium fails because of 'fatigue'(constant expansion and contraction) and then the compressive relationship is lost.

 

 

 

It will displace horizontally on the next weakest point on the material which is circumferential. I've covered this discussion.

 

In all though the circumferential crack is consequential and not causative, therefore not the focus.

 

 

 

My assumption: A significant outward force was exerted to the inside of the headset cup, presumably by a very strong upward force of the fork into the head tube due to play. (very much like driving a taper into the bearing ring).

 

The broken headset cup then sheared the frame.

 

Difficult one. Good luck with the claim.

 

I think its a tough one.

 

The Frame manufacturer will consult the Head set manufacturer/supplier . The headset manufacturer will have the steel and heat treatment analysed in an independent laboratory. The likelihood of a non-conformance is low to zero.

 

I think you had play across (up and down) the steerer.   

 

 

 

 

 

HeartCoppi2010-02-17 15:57:49

[HeartCoppi]

or maybe not...cos weird stuff is known to happen

[100Tours]

not the first time I've see a cracked head tube on a bike of this colour. (maybe it's that celeste paint job.. hmm).

 

The other crack started as a vertical crack on the head tube, then turned as it hit less worked/welded metal. Local agents said something about phoning Rome.

 

[Johan Bornman]

Coppi, thanks for a very interesting perspective.

I get what you're saying but not the weld gas aperture part. The head tube would not require weld apertures since the gas would be free to escape as there is no closed tubes involved.

 

I didn't get to remove the headset race and look inside, that would explain the construction method better since they would have done less machining there to hide the welding.

 

Unfortunately I don't have the frame anymore, it has gone back to Dullstroom and I just had a brief look at it and took some photos for interest sake. However, someone else saw the frame and said he has a similar one at home with a similar crack. I'll ask if I could have a closer look at that one. The chap has gone to SA's for the week and will be back next week I think.

 

The agents didn't even mutter anything about phoning Rome. They just said it is too old to be their problem. Fair enough, these lightweight things are basically consumables.