Holes in seat stay

[lostinthought]

Very good advice from Raynaud. If it were mine, I’d probably just plug the holes myself with some silver solder (easy to do with MAPP gas in a hand held torch, at relatively low temperature) and keep an eye on it. Seatstays generally are fairly thick walled, which will make it more tolerant of this crack-handedness..!

 

[Marchrider]

Let's drill a hole!
No centre punch needed, I've a steady hand Ma'am.
%attempts = 0
:try
inc %attempts
Hmm drill wanders off.
Let's try again.
Hmm drill wanders off.
I don't give up.
Press hard.
Aha!
Drill stays.
Yay a hole.
Oh wrong place.
IF (%attempts < 3) GOTO try
Bah I do give up.
Hmm what should I do.
Scrap metal container?
Hmm gonna first try to sell it.
And then you came to the rescue.

sounds a likely scenario

I have just got myself involved with what could be the entire opposite of that - a model engineer I know has very kindly asked me to build a small steam engine with him, I get to do all the machining and he supervisors and advises on how to achieve the great accuracy needed (it's a wonderful opportunity for me, I can use a lathe and mill but not too this accuracy everything better than 10 microns, i will learn a lot)

yesterday - 2½ hours to drill 8 holes in a casting, and that doesn't inc probably 4 hours milling the casting and positioning it before drilling - they're still to be tapped

 

[wafter]

they're still to be tapped

Presumably freehand after a few beers

 

[Rhythm Thief]

Let's drill a hole!
No centre punch needed, I've a steady hand Ma'am.
%attempts = 0
:try
inc %attempts
Hmm drill wanders off.
Let's try again.
Hmm drill wanders off.
I don't give up.
Press hard.
Aha!
Drill stays.
Yay a hole.
Oh wrong place.
IF (%attempts < 3) GOTO try
Bah I do give up.
Hmm what should I do.
Scrap metal container?
Hmm gonna first try to sell it.
And then you came to the rescue.

Yeah. On the other hand, ten quid. The forks alone will probably fetch that!

 

[JonBuoy]

I would just ride the bike and keep an eye on the 'feature'. Whilst the holes are stress raisers I reckon that the seat stay isn't generally in tension so fatigue crack initiation/propagation is most unlikely and, even if does occur, it shouldn't be catastrophic like a downtube or chain stay failure could be.

You probably want to stop water getting into the tube. I really can't see that brazing will be a metallurgical problem as the rest of the frame is almost certainly brazed!

 

[Illaveago]

I think 2 of the holes are to prevent a split from developing further if one should appear!

 

[Vantage]

I'd echo @Reynard 's comments on this. There's a crap ton of force going through seatstays and when they're as thin as those ones, more reason to worry.
As cyclists we expect to come off the bike now and then but when it happens through frame failure, the results tend to be a bit more catastrophic.

 

[simongt]

Drilliam in the 60's and 70's was a big thing for time trialists in particular. Handle bars and chain rings were often drilled out.

Not forgetting the large flanged hubs that were popular at the time and often drilled as well - !

 

[FrankCrank]

Drilliam in the 60's and 70's was a big thing for time trialists in particular. Handle bars and chain rings were often drilled out.

This sort of thing

Wonder if Mr @mickle has a recommended method to clean these jewels

 

[T4tomo]

The brake levers on my holdsworth are drilled, I think that pretty low risk in terms of structural failure. drilling frame tubes seems a bit darwin-esque

 

[Rhythm Thief]

It'll be up for sale soon. I toyed with the idea of having a new seat stay fitted and having the frame refinished, but I can't afford that (around £400, with decals) and I have no need for the bike or another project anyway.

 

[Drago]

I would just ride the bike and keep an eye on the 'feature'. Whilst the holes are stress raisers I reckon that the seat stay isn't generally in tension so fatigue crack initiation/propagation is most unlikely and, even if does occur, it shouldn't be catastrophic like a downtube or chain stay failure could be.

You probably want to stop water getting into the tube. I really can't see that brazing will be a metallurgical problem as the rest of the frame is almost certainly brazed!

As Dr Reynard CBE mentioned above, the loads on this member are cyclic and that's what will do it in the end.

A constant unvarying tension would indeed likely bring no grief, but that's sadly not a realistic scenario.

 

[JonBuoy]

I don't deny that there is a cyclic component to the loading on the seat stays but this is superimposed on a significant compressive load. I don't actually know but I suspect that this means that the seat stays never see any tensile loading. If this is the case then, as I said before, they will not suffer from fatigue crack initiation/propagation.

 

[Reynard]

I don't deny that there is a cyclic component to the loading on the seat stays but this is superimposed on a significant compressive load. I don't actually know but I suspect that this means that the seat stays never see any tensile loading. If this is the case then, as I said before, they will not suffer from fatigue crack initiation/propagation.

But you'll also get shear forces happening around (and between) the holes.

Even though you're right about the seat stays being in compression as opposed to tension (the ones that are in tension are the chainstays), the load being applied to the structure is neither constant nor always being applied from the same location. Which brings the elastic properties of the frame material into consideration. It's not a pure statics problem anymore, and that stay will fail by buckling as a result of being compromised.

Under normal usage and with no defects, you'd never see a problem. But this isn't normal usage, and those three holes will have a significant effect on the ability of the stay to withstand repeated compressive loading. And it's this, along with the shear forces around those holes, that will eventually make it eventually go "ping"

A very simple analogy would be two drinking straws - one with a pinhole in it and one that's intact. If you put the straw between your hands and push, the straw with the hole will fail more quickly / at a lower load than the one without. And it will buckle right where that hole is.