"Gusset" under downtube

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pwa
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Re: "Gusset" under downtube

Postby pwa » 5 Oct 2019, 11:24am

I don't like those gussets. They look like a cheap afterthought for a frame that wasn't up to the job as it was. But taking one off seems drastic. I'd definitely look for a way of living with it and halting any rust. It is a small area to manage, it has a natural pocket for whatever substance you use, and the opening can be plugged with something like solidified wax. I'd go down that road. It is safe and it is bound to be effective.

jimlews
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Re: "Gusset" under downtube

Postby jimlews » 5 Oct 2019, 12:21pm

slowster wrote:
jimlews wrote:I can't see that it contributes much that is useful on a frame whose purpose is general touring and one that is made from one of Reynolds posher tubesets. Touring bikes have successfully done without such addenda for generations.

1. For generations touring bikes were overwhelmingly lugged, not welded.

2. I think you'll find that there is a gusset on most - possibly even all - 725 touring frames, e.g. Genesis, Dawes, Ridgeback etc. That suggests to me that it is needed and that Reynolds themselves probably specify that a gusset is fitted. I suspect that Reynolds may have had a choice between making the 725 down tube a lot thicker and heavier to allow it to be used without a gusset, or designing the tube to be used with a gusset which would allow it to be lighter and yet just as strong or even stronger.

3. Given the location I would not have worried about water ingress (I take it you are keeping the mudguards on the bike), but spraying Waxoyl into the gap sounds like a good option.

4. If you want an answer from the horse's mouth, ask 531Colin, since he designed the frame.



Re: 1. Lugs serve a rather different function to that of the "gusset"which is a reinforcement. Lugs are just a convenient way of joining the tubes. It is the accurate mitering of the tube ends that is the important thing. That and complete penetration of the brazing material. Lugs were routinely filed to reduce the step ratio between the tube and the lug and thus reduce the risk of introducing a stress riser.

Re: 2. 'a gusset on most - possibly even all'... suggests that it is needed...
It could equally suggest that either all those frames are made in the same Taiwanese factory or it is merely the current fashion accessory.

Re: 3. Picture the scene. It is raining. I have mudguards fitted. Consequently, I am less wet than I would have been. But the rain is landing on the bike frame; perhaps only on the top, but then it then runs around the sides of the tubes to the underside where it is drawn beneath the gusset by osmosis.

Re: 4 How could you possibly know that? I haven't put a name to the frame.

simonhill
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Re: "Gusset" under downtube

Postby simonhill » 5 Oct 2019, 12:42pm

David9694 wrote:A picture would be good.

I’ve never seen this before. I note people seem to recognise it, but are you sure it’s not a repair to a front end shunt?


I'm with David.

We get lots of pictures of the bl**din obvious on the forum, how about one of the relatively obscure.

Please.

pwa
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Re: "Gusset" under downtube

Postby pwa » 5 Oct 2019, 12:48pm

Is it just me, or is there something a bit dodgy about requesting folk send in pictures of their gussets? :D

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horizon
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Re: "Gusset" under downtube

Postby horizon » 5 Oct 2019, 1:02pm

David9694 wrote:A picture would be good.

I’ve never seen this before. I note people seem to recognise it, but are you sure it’s not a repair to a front end shunt?


From Chris Juden's review of the Spa Tourer:

I can’t fault the geometry or tubing choice and was pleased to see a
reinforcing plate under the down-tube/head-tube joint. I think lugless frames
often need a bit of stiffening there (the Spa Ti frame now also has this).

Let's just get Brexit done so that we can get on with the important job of re-joining the EU!

jimlews
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Re: "Gusset" under downtube

Postby jimlews » 5 Oct 2019, 1:56pm

horizon wrote:
David9694 wrote:A picture would be good.

I’ve never seen this before. I note people seem to recognise it, but are you sure it’s not a repair to a front end shunt?


From Chris Juden's review of the Spa Tourer:

I can’t fault the geometry or tubing choice and was pleased to see a
reinforcing plate under the down-tube/head-tube joint. I think lugless frames
often need a bit of stiffening there (the Spa Ti frame now also has this).



Yes, I was surprised to read that.

Perhaps it indicates that even the most sagacious are not always right? :wink:

pwa
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Re: "Gusset" under downtube

Postby pwa » 5 Oct 2019, 2:00pm

But Thorn don't see a need for them on their Club Tours, of which I have one, and you don't hear a lot of stories of those falling apart.

https://www.sjscycles.co.uk/frames/550l ... tal-imron/

Brucey
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Re: "Gusset" under downtube

Postby Brucey » 5 Oct 2019, 2:34pm

Image

this gusset is on a BMX frame, but is similar in principle to those found on other frames such as those under discussion.

The bottom of the down tube to head tube weld is one of the most stressed on a bike. Cracks of this sort

Image

are not unusual on framesets that are not strong enough /reinforced enough at this point.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

jimlews
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Re: "Gusset" under downtube

Postby jimlews » 5 Oct 2019, 3:32pm

Thanks for posting the pics, Brucey. You've saved the blushes of an incompetent photographer.

The welding on the BMX frame is BEAUTIFUL. I could sit and admire it all day!

That in the second picture is, I think less good. Somewhat uneven. Is it mere coincidence that the crack propagates from where the weld starts/finishes - under that blob?

Brucey
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Re: "Gusset" under downtube

Postby Brucey » 5 Oct 2019, 3:50pm

the second photo is (for my convenience) of an aluminium frame; it was the first photo I found which showed the right kind of things. It is indeed no coincidence that the cracks have started at the weld overlap. For various reasons these welds won't look as nice as typical TIG welds in steel.

Most people can get their heads around the idea that nasty notch-like features (eg at the edge of the weld) can act as crack starters. However there are (literally) unseen forces and effects at work. These include;

- residual stresses and
- changes in the material due to the thermal cycle.


The latter varies with the material concerned, but let's put it this way; it is almost invariably the case that the material isn't improved by seeing the thermal cycle from welding/brazing. If it were, the tubing would see that thermal cycle during manufacture, instead of being deliberately made less well than it could be.….

Residual stresses are a bit easier; you can take it as read that the stresses in a weld (without stress-relief (heat) treatment) are yield magnitude. How local residual stresses interact with applied service stresses is not simple, not simple at all, and yet can affect the fatigue life of the structure.

The net effect of all this is that the (fatigue) life of nearly all welded structures is limited by the welded joints themselves, but the service stresses that the structure sees can also make the fatigue life expectancy vary somewhat.

cheers
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Vantage
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Re: "Gusset" under downtube

Postby Vantage » 5 Oct 2019, 4:11pm

The lug requested...

IMG_20191005_160645.jpg

I personally wouldn't remove it.
As suggested up-thread, I'd fill it with silicon or some other gooey stuff that dries hard.
If it all went pear-shaped during its removal then you'll have bollo**d up a perfectly good frame.
Bill


“Ride as much or as little, or as long or as short as you feel. But ride.” ~ Eddy Merckx
It's a rich man whos children run to him when his pockets are empty.

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Vantage
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Re: "Gusset" under downtube

Postby Vantage » 5 Oct 2019, 4:15pm

simonhill wrote:
David9694 wrote:A picture would be good.

I’ve never seen this before. I note people seem to recognise it, but are you sure it’s not a repair to a front end shunt?


I'm with David.

We get lots of pictures of the bl**din obvious on the forum, how about one of the relatively obscure.

Please.


Not a repair from a shunt. It was there when I bought it new from Spa.
Bill


“Ride as much or as little, or as long or as short as you feel. But ride.” ~ Eddy Merckx
It's a rich man whos children run to him when his pockets are empty.

reohn2
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Re: "Gusset" under downtube

Postby reohn2 » 5 Oct 2019, 4:58pm

jimlews wrote:I am thinking that if I remove it carefully, there should be no reduction in the strength of the frame. I understand that 725 steel becomes harder due to the welding process (hopefully, not embrittled), so the aprox 38mm of heat affected area down each side of the downtube should be at least as strong as it was when it left the tube factory.

There is already evidence of rust grinning through at the 'lip'. This can be wiped away, but it is obvious that something untoward is happening within.

In my version of cycle-touring, I am regularly following muddy, empuddled tracks and fording streams, so moisture IS going to find its way into the gap, mudguards notwithstanding.

In my experience in a past life, of restoring old motor cars, Waxoyl makes any subsequent painting problematic,to say the least.

And finally, what better way is there of spending those long winter evenings than by 'whittling' ones bicycle?

Never had a problem with Waxoyl spoiling the paint any of the frames I've used it on.
I can't think why I'd want to deliberately weaken a frame,especially in one of the areas where it's stressed most.I've two frames(Genesis) with similar gussets never had a problem with them after a Waxoyl treatment.
You asked for advise mine is don't do it,but it's entirely upto you.
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alexnharvey
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Re: "Gusset" under downtube

Postby alexnharvey » 5 Oct 2019, 5:13pm

I whittle my bikes in the middle of the tubes, not at the ends where they see the highest stresses.

PH
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Re: "Gusset" under downtube

Postby PH » 5 Oct 2019, 5:38pm

No gusset on my 725 Hewitt tourer.
But if the designer thinks it’s better with one and you disagree, you’ve bought the wrong bike.