Gouge in 631 steel frame

[David9694]

As we’re all sharing pictures of our dings, here’s mine from last year. I filled it in with Polyfilla. It’s on the underside of the 531 down tube, about the depth of an almond kernel split across lengthways. “Keep any eye on it” seems like the consensus - which seems like a sensible course for the OP.

[bgnukem]

I had a would be thief try and steel my dawes Horizon that has a 531 steel frame , he/she/it then decided to destroy the frame with a supermarket trolly as it found the bike was locked up too well. The pont of all this I was surprised how thin the steel tube was, so I am a bit wary of dents and such like in steel frames.

Well with wall thicknesses around 0.5mm for 531C (not sure about 631, but various gauges available in each tubeset in any case) there's not too much material to play with! For that reason I've always been paranoid about corrosion inside tubes and have tended to fill my frames with waxoyl before using the bike, and immediately touching up any paint chips.

Also I guess the potential for buckling of the tube under load becomes an issue if the basic shape of the tube cross-section has been compromised. I understand some bike tubes are probably close to the buckling limit though right now I cannot find a simple formula for this.

[bgnukem]

23A05DE6-1014-4DFA-A33B-D779FAEAD7E8.jpeg

As we’re all sharing pictures of our dings, here’s mine from last year. I filled it in with Polyfilla. It’s on the underside of the 531 down tube, about the depth of an almond kernel split across lengthways. “Keep any eye on it” seems like the consensus - which seems like a sensible course for the OP.

That looks a lot more serious than the OP's dent! Not sure I'd be happy riding that.

Going to be difficult to detect any incipient cracking if the dent is filled with polyfilla!

[JohnW]

23A05DE6-1014-4DFA-A33B-D779FAEAD7E8.jpeg

As we’re all sharing pictures of our dings, here’s mine from last year. I filled it in with Polyfilla. It’s on the underside of the 531 down tube, about the depth of an almond kernel split across lengthways. “Keep any eye on it” seems like the consensus - which seems like a sensible course for the OP.

Frippin' 'eck David - that would worry me. I suppose that it depends to some extent on where on the down-tube, but it would worry me. Of course, depending on how many miles it's done since it happened. Some may accuse me of being over-cautious. 531 is resilient stuff of course, but it would worry me.

How did it happen?

[Brucey]

any dangers of cracking in a steel frame don't pose the quite same risk as cracks in other frame materials. The reason is that in steel frames, as the crack progresses, the frame almost invariably goes all floppy before it lets go completely.

cheers

[David9694]

It was a second hand purchase - I guess the bike ran into a stone and it looks like it’s been there a while. It rides very nicely, but once you’ve got a known issue, it becomes a focus for worry. I won’t be loading it up heavily.

There does seem to be a lack of any science around this issue - like when and where do frames of the various material fail? My only experiences are (i) a Raleigh Medale being returned to us a couple of weeks after purchase in my Halfords days because the bottom bracket/seat tube joint had failed (ii) from childhood, the joint between the main tube and front tube on my Moulton broke because I bumped it up a kerb once too often (iii) crashing into a parked car quite badly - I remember our neighbour putting a broom handle down the head tube and righting it to some extent - it stayed in the family in that state for some while as I recall. When I crashed a couple of years ago a carbon bike, I stopped using the frame, even though there was no evidence or reason to believe it was damaged - the front wheel bore the brunt.

[Brucey]

a stone did that? No way. I think the suggestion upthread that it was the brake caliper or something similar is more like it. I've seen damage like it before, where the handlebars swing round, and the brake caliper slides under the down tube, scratching the paint on the way through. Numpty then turns the handlebars back the other way and of course the brake won't slide back so easily and that is when the dent is made. The caliper is then moved and forced back. I think this explains the lower, upper(with dent) and middle marks respectively in the picture.

In terms of real 'damage' this is slight. The lever bosses are probably a greater stress concentration and a bigger threat to the integrity of the frame. Go ahead and have the frame refinished, you won't even see a dent just there unless you look for it. Just keep an eye on it from time to time and make sure it doesn't turn into a crack.

cheers

[dim]

email Bob Jackson and ask them for their opinion .... if that tube needs replacing, they can do it (their frame resprays are also quality)

[peetee]

To me it looks very much like the sort of damage that a cassette on a removed back wheel would do when it's all loaded into the back of a car.

[pwa]

I once had a 725 frame with internal cable routing that I didn't like so I got Argos Cycles to fill the holes in the top tube with braze and attach external cable stops. They thought that would be okay and it seems to me that your little dent is less of a breach in the integrity of the tube. So for me it would come down to the best way to address the cosmetic damage. Braze would do it.

[JohnW]

I once had a 725 frame with internal cable routing that I didn't like so I got Argos Cycles to fill the holes in the top tube with braze and attach external cable stops. They thought that would be okay and it seems to me that your little dent is less of a breach in the integrity of the tube. So for me it would come down to the best way to address the cosmetic damage. Braze would do it.

These are just my thoughts - I'm not a metallurgist nor an engineer, and these are just my thoughts.............but in the case of a frame with internal cable routes the aperture in the tube wall is designed, not accidental, and (in theory at least) designed for the situation. The apertures are of a designed shape for stress distribution and are trimmed around the edges (at least, the ones that I've seen are) with steel to also distribute and spread the stresses. Any braze fill is just a filler, not structural.

In the case of damage, where the steel is holed or cracked the stresses set up in the steel by flexing of the frame in use can concentrate on the hole/crack and make the damage worse, increasing the size of the hole and developing the cracks into a hole. Filling a damaged/cracked/holed tube with braze is an attempt at a structural repair and I'm not sure that it would perform as such.

Steel performs better under these circumstances than alu or (I'm given to understand) carbon - dunno about titanium, but everything has it's limits. I think I'd approach the damage under discussion by sandpapering the paint and rust off and get down to the bare, shiny metal and inspect it then. I certainly wouldn't have bought that frame, and in the light of what is visible on the photographs, I'd worry.

[Brucey]

filling dents with braze metal is common practice. Of course it helps with redistributing service stresses (if it didn't, you wouldn't ever have much luck with fillet-brazed frames...) but there is a down-side; the heat does things to the steel including adding a new lot of residual stresses.


Even so a bottle braze-on or a gear boss braze on is much more likely to be the starting point for a fatigue crack than either a braze-filled dent (of almost any size) or a small dent that is left unfilled.

cheers

[JohnW]

filling dents with braze metal is common practice. Of course it helps with redistributing service stresses (if it didn't, you wouldn't ever have much luck with fillet-brazed frames...) but there is a down-side; the heat does things to the steel including adding a new lot of residual stresses.


Even so a bottle braze-on or a gear boss braze on is much more likely to be the starting point for a fatigue crack than either a braze-filled dent (of almost any size) or a small dent that is left unfilled.

cheers

Yes - a dent is one thing, but a crack or a hole is something different - or is/isn't it? Do you say that a braze fill fully restores integrity if the tube-wall is holed or cracked? - a lot also depends upon the bond between the braze and the steel - preparation will be everything, wouldn't it? I'm just interested, not arguing.

[Brucey]

the braze metal helps redistribute the stresses. Very roughly this is pro-rata with thickness, so if a 2mm deep dent in 0.5mm wall thickness tubing is filled, the service stresses are going to be locally reduced by at least 80%, because that area is five times thicker now. I say 'at least' because the stress concentration factor is also reduced in a good repair; cracks become less crack-like and so forth.

Repairs are not an exact science, but then new bike frames aren't either.

cheers

[David9694]

I should have said that my dent is about one quarter of the way up from the b/b. It would be outside of the radius of the chainwheel but not by much. It does seem to have struck or possibly fallen onto something. I wouldn't have infilled it if I thought it was likely to be the source of further problems. It’s too old to have braze on lever bosses,