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Engineers: Cause of frame failure. Vent holes?

nickaziz

Monkey
Aug 4, 2004
261
0
This question is mainly aimed at engineers and frame builders.

The downtube on my frame cracked where it connects to the head tube, and eventually the down tube broke free (I was waiting to crash replace the frame so I didn't stop riding it). I recently just noticed that there are big cracks coming from the "vent holes" that are drilled in the head tube. Two large cracks come from the center of either side of the lower vent hole. Could the fact that the frame broke be a result of vent holes that were too large?

An Easton guide on frame building says: "Also, extra large holes can weaken overall strength of the joint, especially at the connection of the head tube to down tube. Use extra care to center large vent holes with the tube."

:think:
 

buildyourown

Turbo Monkey
Feb 9, 2004
4,832
0
South Seattle
How big is the vent hole? Is it centered? Is it deburred?
On steel bikes, a 1/4" hole is the standard and it should be well deburred. The holes are larger on aluminum frames.

Did the weld crack? Or did a chunk of the HT fall off? I don't think I've ever seen a failure where the headtube cracked and only part of it seperated.
The area around the vent hole is very low stress.
 

nickaziz

Monkey
Aug 4, 2004
261
0
It's a 4130 frame and the hole is about 3/4" in size. It's strange because the down tube cracked all the way around the weld (adjacent to it, not through it). Also, on the outside of the frame you could see very faint cracks perpendicular to the down tube crack/weld. I believe these faint cracks correspond to the major cracks you can see coming from the vent hole.
 

buildyourown

Turbo Monkey
Feb 9, 2004
4,832
0
South Seattle
3/4" seams huge for a steel frame. Completely unnecessary. Is this a highend frame or a cheaper frame? I understand if you don't want to post the brand. You can PM me if you want. Is there any sign of weld undercut? This is common on many steel frames. If the welder doesn't use enough fill, it will create a thin spot in the tube adjacent to the weld bead. Perhaps the crack started on the weld and stopped at the hole.
 

nickaziz

Monkey
Aug 4, 2004
261
0
I'll post a picture here that doesnt reveal the brand or type of bike. I'll PM or email you more detailled pics if you wish.
 

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buildyourown

Turbo Monkey
Feb 9, 2004
4,832
0
South Seattle
That pic is scary. The hole is waaaay too big and the finish on the edge is all jagged. That bad finish means stress risers.

I would venture to say that that hole is too big to give proper argon flow. The point of vent holes is to control the flow of argon while TIG welding. Holes closer to the purge fittings are bigger. ie, headtube, dt, bb. Holes farther away are smaller. ie, chainstays, seatstays. If the holes are too big, the gas flows too fast and you get oxidization on the backside of the weld. However, you'll never know until it fails.
 

Brian HCM#1

MMMMMMMMM BEER!!!!!!!!!!
Sep 7, 2001
32,119
378
Bay Area, California
I don't know why people feel they can't say what manufacture cracked, it could possibly save someone if their's were to crack in the same place. It not directed towards bashing any company its just helpful information.
 

buildyourown

Turbo Monkey
Feb 9, 2004
4,832
0
South Seattle
Brian HCM#1 said:
I don't know why people feel they can't say what manufacture cracked, it could possibly save someone if their's were to crack in the same place. It not directed towards bashing any company its just helpful information.
I understand. Maybe he has a hookup. Maybe he is giving the company a chance to make things right before bad mouthing them on a public forum.
 

nickaziz

Monkey
Aug 4, 2004
261
0
Because this isn't a widespread problem, I don't want to make it look like it is, because that's what the Internet seems to do. I initally believed the frame broke due to fatigue etc, but now I am starting to wonder if there were some design/manufacturing flaws.

buildyourown: did you get the pics?
 
ANY manufacturers bike can break. It's how that company's customer service handles the deal that's important.

From what I can see, that bike looks like an obvious warranty to me. And if the company stands behind it, i see no bashing, maybe even some good PR for a company backng up their product.
 

Brian HCM#1

MMMMMMMMM BEER!!!!!!!!!!
Sep 7, 2001
32,119
378
Bay Area, California
buildyourown said:
I understand. Maybe he has a hookup. Maybe he is giving the company a chance to make things right before bad mouthing them on a public forum.
Thats a crock, who cares, if theres a problem or something fatigue related let people know, its not like you're saying this is a POS and these frames suck. Maybe it is manufacture related and removing a fork may show the similar cracks.
 

Acadian

Born Again Newbie
Sep 5, 2001
714
2
Blah Blah and Blah
Brian HCM#1 said:
Thats a crock, who cares, if theres a problem or something fatigue related let people know, its not like you're saying this is a POS and these frames suck. Maybe it is manufacture related and removing a fork may show the similar cracks.
it's a Karpiel.. :rolleyes:
 

OGRipper

back alley ripper
Feb 3, 2004
10,647
1,116
NORCAL is the hizzle
I respect keeping the brand quiet, there are lots of reasons to do it. If it turns out to be a real issue that affects other people the company should be the one to handle it, issue a recall, etc. If it's that kind of problem and the company fails to address it, THEN let 'em be called out on a public forum. Many of us can tell the difference between something that is not company's fault and something that is, but lots can't, and the negative PR could really hurt, especially if it's a smaller, newer company.

Anyway if the standard is a 1/4" hole that looks pretty sketchy to me.
 

Fulton

Monkey
Nov 9, 2001
825
0
Acadian said:
it's a Karpiel.. :rolleyes:
it may have been a karpiel, but I'm sure the fault lies in the damn risse crowns he's running on his stratos fork. :) just messin with ya brain hehehe
 

OGRipper

back alley ripper
Feb 3, 2004
10,647
1,116
NORCAL is the hizzle
Brian HCM#1 said:
And if thats on every frame, wouldn't you want to know? Its not product bashing, its useful information.
Well like I said, if it's something that affects other people the company should take care of it via recall. If it's on every frame the company should address it. If they don't Nickaziz can re-post what's up. Part of my point is that sadly lots of people who show up here read something negative and immediately start telling all their friends, who tell other people, and suddenly an issue that could be limited to one or a few bad frames (possibly built by a outside supplier) ends up really hurting a solid company.

You'd probably feel differently if it was your company, even if you don't want to admit it. It's not about hiding the truth, it's about managing PR.
 

binary visions

The voice of reason
Jun 13, 2002
22,092
1,132
NC
It's my opinion that the manufacturer should be contacted first, before telling the whole world what happened. That way, the post that tells the whole world what happened can be complete and informative.

There's a huge difference between a passerby reading:

"My Turner's headtube cracked off. See? PICTURES! Dammit."

and

"Last week, my Turner's headtube cracked off. I called Turner and they were very helpful. They indicated that they had not seen the problem before, but a new frame would be sent out the next day for me, if I would send my frame back so they could inspect it. The new frame showed up today. Here's pictures of my cracked headtube, and here's pictures of my beautiful new Turner!"

Doesn't that second paragraph represent what happened better than the first one? There was a problem, and the company was given the opportunity to make it right, and they did.

I agree that people should be informed of problems, and I would hope that nickaziz comes back and informs us what happened with the frame after he discusses it with the manufacturer. That allows people to both be informed, and not spread bad information.
 

Brian HCM#1

MMMMMMMMM BEER!!!!!!!!!!
Sep 7, 2001
32,119
378
Bay Area, California
OGRipper said:
Well like I said, if it's something that affects other people the company should take care of it via recall. If it's on every frame the company should address it. If they don't Nickaziz can re-post what's up. Part of my point is that sadly lots of people who show up here read something negative and immediately start telling all their friends, who tell other people, and suddenly an issue that could be limited to one or a few bad frames (possibly built by a outside supplier) ends up really hurting a solid company.

You'd probably feel differently if it was your company, even if you don't want to admit it. It's not about hiding the truth, it's about managing PR.
The people who know me will tell you the samething, I'm a blunt right to the point type of guy, if I have a problem with something I'm not afraid to speak up and tell it how it is, if people take offense oh well, I don't fret the small things. Some people have no problem bashing a company they've never dealt with so I see no problem with it.
 

OGRipper

back alley ripper
Feb 3, 2004
10,647
1,116
NORCAL is the hizzle
Brian HCM#1 said:
The people who know me will tell you the samething, I'm a blunt right to the point type of guy, if I have a problem with something I'm not afraid to speak up and tell it how it is, if people take offense oh well, I don't fret the small things. Some people have no problem bashing a company they've never dealt with so I see no problem with it.
\


Well, good for you Brian, we can all aspire to your level of honesty. Keep it real brah. :rolleyes:

Personally I DO have a problem with people bashing a company they know nothing about. I'm kind of surprised, is that really what you meant to say? Seems like not too long ago you had a problem with people bashing Karpiel when they didn't really know what they were talking about.
:think:
 

binary visions

The voice of reason
Jun 13, 2002
22,092
1,132
NC
OGRipper said:
Seems like not too long ago you had a problem with people bashing Karpiel when they didn't really know what they were talking about.
:think:
Actually, it went way beyond that... Everyone was instructed to be quiet if they didn't have personal involvement with Jan himself.

Isn't this pretty close to that situation, Brian? He doesn't know what the situation is, really, since he hasn't talked to the company. So he's nicely being quiet until he finds out what happened and what their response is.
 

OGRipper

back alley ripper
Feb 3, 2004
10,647
1,116
NORCAL is the hizzle
Yeah it's a complete reversal of principals but whatever, let's not fret the small things. :D

Anyway, I'm curious what happens with this frame, Nickaziz it would great if you can give us an update at some point.
 

wirly

Monkey
Mar 19, 2002
110
0
San Diego
Brian HCM#1 said:
Some people have no problem bashing a company they've never dealt with so I see no problem with it.
:confused: I don't know what to say...ummm...way to stand up for some other people's lack of judgement and use it to justify yours...?

Stick to your guns if you believe bashing a company without having any real input is lame.
 

dw

Wiffle Ball ninja
Sep 10, 2001
2,943
0
MV
Head tube vent hole size wont have a significant effect on strength within reason. 3/4 of an inch head tube vent hole with a 1.375 or 1.5 inch DT/TT on a steel bike, assuming "normal" loading and "normal" wall thicknesses will not pose a safety problem or increase in possibility of cracking. Poor post machining cleanup of burrs etc can have an effect though.

dw
 

nickaziz

Monkey
Aug 4, 2004
261
0
^ Thanks. I was hoping you would reply. :) Do the cracks coming from the hole look like they could have happened as a result of the down tube breaking free, or does it look like something that was happening at the same time/before the dt weld cracked?
 

nickaziz

Monkey
Aug 4, 2004
261
0
P.S. faint cracks that seem to correspond to the internal vent hole cracks were apparent on the outside of the frame before the down tube broke off. At that point, the crack on the underside of the down tube was only 1mm spread or so.
 

CreeP

Monkey
Mar 8, 2002
695
0
montreal bitch
My guess is it has to d with the welding of the gusset. I can't see too many ways for cracks to occur right there without some accidental difference in temper between the top half of the dt/ht junction and the bottom portion where the gusset was added.
That's my best guess but i'm unsure of it's accuracy, it's a weird looking damage that doesn't correspond with my intuition for the forces in that area.
 

dw

Wiffle Ball ninja
Sep 10, 2001
2,943
0
MV
I have no idea, I mean, it could have been something that happened due to a lot of different things. Steel fatigues just like aluminum and titanium. It also can fail catastrophically too. Could have been a TON of differnt things, a combination of factors, etc... As long as youre safe, thats the most important thing.

Dave
 

dw

Wiffle Ball ninja
Sep 10, 2001
2,943
0
MV
curious, what are the hole diameters in the head tube, head tube wall thickness at the holes, and DT/TT diameters?
 
Yea I agree with not releasing the bike manfactures name until it is all over and done. I had a problem with my frame that needed and whole new frame, and lets say I wasn't impressed with anything about this company after I had the frame in my hands. The frame was great, but cant say for the custmer service, but I think thats getting worked out....well I hope so.
 

nickaziz

Monkey
Aug 4, 2004
261
0
dw said:
curious, what are the hole diameters in the head tube, head tube wall thickness at the holes, and DT/TT diameters?
The holes are 3/4, the TT is 1.5, the DT is basically the same size. The head tube wall is at most 1/16th.