"Gusset" under downtube

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slowster
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Re: "Gusset" under downtube

Postby slowster » 5 Oct 2019, 6:48pm

jimlews wrote: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.

The point remains that they are quite different methods of joining tubes, and are likely to have different failure modes, as illustrated by the posts above. Inferring that the gusset is not necessary because for generations frames had no such reinforcement, when those frames were overwhelmingly lugged, is specious logic.
jimlews wrote: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.

Contract frame manufacturers will make whatever someone pays them to. They will not be concerned if a brand orders a batch of frames with an inherently weaker design that they suspect - or know - will result in an unacceptable number of breakages and returns, because it is not their reputation that will be damaged and they will not have to pay for replacement frames. They might query the order in the interests of maintaining a good customer relationship, to give the brand the opportunity to change the design, but that would probably be the most they would do. Similarly they will not do anything that the brand has not requested - the order could be rejected, and adding a gusset will increase the cost of a frame.
jimlews wrote:Re: 4 How could you possibly know that? I haven't put a name to the frame.

I'm psychic.
Last edited by slowster on 5 Oct 2019, 6:56pm, edited 1 time in total.

fastpedaller
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Re: "Gusset" under downtube

Postby fastpedaller » 5 Oct 2019, 6:56pm

I squirted waxoyl (well, ok the Lidl equivalent :D ) into that area 5 years ago on my Spa tourer and it's caused no problem. I have to say I think waxoxl is a superb product (and the Lidl one seems as good)…….. Many years ago on one of my kit cars I noticed a chassis member was receiving drips of water through the bonnet join above and was rusty after only a few months. Without even cleaning off the rust or applying more paint, I splashed some Waxoyl on it with a brush and it shrugged off any water in the following 2 years until I sold the car. Apparently it (Waxoyl) can cause an adverse reaction with GRP (Glass reinforced plastic or Fibreglass) so keeping it away from any plastic parts is probably a good idea. I would leave well alone (apart from adding some waxoyl or similar)

fastpedaller
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Re: "Gusset" under downtube

Postby fastpedaller » 5 Oct 2019, 7:01pm

slowster wrote:Contract frame manufacturers will make whatever someone pays them to. They will not be concerned if a brand orders a batch of frames with an inherently weaker design that they suspect - or know - will result in an unacceptable number of breakages and returns, because it is not their reputation that will be damaged and they will not have to pay for replacement frames. They might query the order in the interests of maintaining a good customer relationship, to give the brand the opportunity to change the design, but that would probably be the most they would do. Similarly they will not do anything that the brand has not requested - the order could be rejected, and adding a gusset will increase the cost of a frame.


Is that an accurate statement? The youtube video of Maxway cycle production is worth a look, and shows some of the frame testing they do (I can't imagine they've made a test rig just for the video :lol: ). They may or may not be typical of far east production?

PH
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Re: "Gusset" under downtube

Postby PH » 5 Oct 2019, 9:44pm

slowster wrote:Contract frame manufacturers will make whatever someone pays them to. They will not be concerned if a brand orders a batch of frames with an inherently weaker design that they suspect - or know - will result in an unacceptable number of breakages and returns, .

Do you have any evidence that’s the case? Do you not think if the 725 un-gusseted frames from the likes of Thorn and Hewitt, which have been around for decades, were failing they would have done something about it? And the contractor doing the manufacturing will have an input in the way it’s built, they will prefer to stick with stuff they’re already successful with and they very much have a reputation to maintain.
I see it as simple- if you don’t trust the brand, don’t buy from them. If you do trust them you accept their choices.

Brucey
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Re: "Gusset" under downtube

Postby Brucey » 5 Oct 2019, 10:13pm

worth mentioning that before comparing frames with and without gussets, it is worth looking at the tube gauges/materials used, and the intended service.

Colin hasn't said as much, but I'd imagine that extended rough-stuffing/hard use of spa prototypes may have revealed an advantage to having a gusset (even if it is only to give a safety margin), whereas there might be no appreciable benefit in deleting it.

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

David9694
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Re: "Gusset" under downtube

Postby David9694 » 6 Oct 2019, 9:10am

My Genesis Equilibrium 853 is fillet brazed. I’m not an engineer but I do marvel at the strength of this type of joint, given how they’re done (the other guy on the 2015 Downland Cycles course went lugless and we both did practice joints).

No gusset on my Spa Ti Audax - should I be worried??

We sure have drifted from the OP’s question “how do I prevent getting a rusty gusset?”!

PH
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Re: "Gusset" under downtube

Postby PH » 6 Oct 2019, 11:11am

David9694 wrote:We sure have drifted from the OP’s question “how do I prevent getting a rusty gusset?”!

The original question was about it’s removal. We haven’t drifted that far, though such is the nature of discussion.

reohn2
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Re: "Gusset" under downtube

Postby reohn2 » 6 Oct 2019, 12:10pm

What puzzles me mostly about the suggestion of removing the gusset is how does it improve anything.
Remove the gusset and there's a)a chance the frame will be weakend,b) the area where it's been will need smoothing off,treating and painting,c)there's also a fair bit of work needed to do the job properly.
All for what,when a squirt of Waxoyl or even aerosol waterproof grease would stop any internal rusting or ingress of water and muck.
I'm truly surprised and amazed anyone would contemplate such a modification.
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slowster
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Re: "Gusset" under downtube

Postby slowster » 6 Oct 2019, 12:21pm

PH wrote:Do you not think if the 725 un-gusseted frames from the likes of Thorn and Hewitt, which have been around for decades, were failing they would have done something about it?

Whilst they are all 725 we do not know that the Thorn and Hewitt frames use fundamentally the same down tube and head tube design. The tubes might be a different profile and there might be differences in the manufacturing methodology, e.g. some steel frames are heat treated to increase their strength. Surly's Long Haul Trucker is (generic?) cro-mo and does not have a gusset, and given its reputation as a very tough frame which is often chosen for heavy duty touring, I presume that Surly have used relatively thicker/heavier tubing.

Ultimately all frames will fail, and what matters is whether the rate of failures is acceptable to the brand that orders the frames. I think the last 20+ years have seen an increase in customers who will accept a frame cracking after what many others would consider an unacceptably short lifespan, something which I think reflects the widespread use of lightweight aluminium frames and customers who are/have been MTBers who destroy/change/replace frames and bikes every few years.

Brands will factor in a percentage of frame failures and refunds/replacement frames into their pricing. If the frames have a high profit margin, they can afford more frame failures, and conversely the more competitive the price, the more important to the brand that frame failures are as low as possible. I think Spa and its value for money focused customers will be far less tolerant of frame failures than some other UK frame brands and many of their customers.

PH wrote:And the contractor doing the manufacturing will have an input in the way it’s built, they will prefer to stick with stuff they’re already successful with and they very much have a reputation to maintain. I see it as simple- if you don’t trust the brand, don’t buy from them. If you do trust them you accept their choices.

I agree, with one important caveat: the manufacturer only has a reputation to maintain with its customers. It does not have a reputation to maintain with you or me, because we do not know who the manufacturer is. 531Colin has commented in passing on the forum that he did not ask the factory that makes Spa's frames to use 725 stays, because he considered it better for them to use and work with the cro-mo stays which they usually used and were already very familiar with. I'm sure there was a good bit of two way discussion between Spa and the factory in the course of going from a design and making prototypes, before manufacturing the first batch of a new frame. I have bought a Spa frame in part precisely because of Spa's/531Colin's conservative approach to designing the frames, and that includes things like having a gusset.

Brucey
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Re: "Gusset" under downtube

Postby Brucey » 6 Oct 2019, 1:03pm

reohn2 wrote:What puzzles me mostly about the suggestion of removing the gusset is how does it improve anything.
Remove the gusset and there's a)a chance the frame will be weakend,b) the area where it's been will need smoothing off,treating and painting,c)there's also a fair bit of work needed to do the job properly.
All for what,when a squirt of Waxoyl or even aerosol waterproof grease would stop any internal rusting or ingress of water and muck.
I'm truly surprised and amazed anyone would contemplate such a modification.


Me too.

It is not as if you will end up with a frame that is 'just like it would have been without a gusset'. It won't be like that at all;

a) the weld overlap on the down tube weld may have been done differently to how it should have been done without
b) the weld beads from the gusset can only be smoothed externally; some geometric features (stress raisers) may remain
c) there is a HAZ (heat affected zone) from the gusset welds (with worse properties) whether there is a gusset there any more or not.

Makes no sense to me at all.

cheers
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David9694
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Re: "Gusset" under downtube

Postby David9694 » 6 Oct 2019, 5:28pm

Is there a good reason why the - ahem - “reinforcement plate” was left open at one end?

I'd leave it Where it is.

pwa
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Re: "Gusset" under downtube

Postby pwa » 6 Oct 2019, 5:52pm

The fact that Thorn, who I associate mostly with overbuilt rock solid frames, does not seem to use gussets on any of its frames makes me think gussets are taking the "belt and braces" approach a bit too far when used with 725 tubes. But if I had a 725 frame with a gusset I would not let it bother me. It is aesthetically a bit rubbish but I have more important things to worry about.

jimlews
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Re: "Gusset" under downtube

Postby jimlews » 6 Oct 2019, 9:59pm

OK, probably time to put this one to bed.

I've just got back from an 'excursion' and happen'd to get talking to a chap who turned out to be a metallurgist/mechanical engineer (not the same thing, apparently).I ran this question past him. The gist was that the frame didn't need a gusset in the first place but, now its got one, it certainly does. So broadly in line with Brucey's last post and also what the 'don't do it' folk (about 100% of them) here are saying.

Needless to say, the gusset stays and I go down the Waxoyl and hairdryer route.

My thanks to all who contributed their knowledge, sage advice and opinions.

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horizon
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Re: "Gusset" under downtube

Postby horizon » 6 Oct 2019, 10:07pm

jimlews wrote:OK, probably time to put this one to bed.



Though like all naughty children it is quite likely to want to stay up a lot longer. :mrgreen:

Even if you hadn't wanted to cut it off, it was still a good question. I have a Spa tourer frame which I am currently building up. I like the idea of the strengthener but now that it has been queried I would like to know more. I cannot imagine that many bike frames get such a forensic examination as the Spa frame has had on this forum (on multiple threads) but until we hear from Spa or the frame's originator we are really none the wiser. In fact, I am surprised it hadn't been raised long ago.
Let's just get Brexit done so that we can get on with the important job of re-joining the EU!

slowster
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Re: "Gusset" under downtube

Postby slowster » 6 Oct 2019, 10:17pm

jimlews wrote: the gusset stays and I go down the Waxoyl and hairdryer route

When you do it, be aware that there is/may be a gap in the join between the down tube and head tube, such that if you intend to fill the void up with Waxoyl, that will not happen. Instead of seeing the Waxoyl eventually start to overflow from the gusset opening, what you will instead find is that there is a lot of Waxoyl that has flowed into the down tube and thence into the head tube.

DAMHIKT.