Fill-brazing rear bridge on track frame - possible?

Hi,

I have a track frame that has a cutout at the rear bridge. To make the clearances a bit more perfect, I have filed out the cutout a bit more than it was before, and now it's really perfect.

But, due to structural reasons, I am thinking about filling/closing the tube to make it solid. Is that possible with brazing alone, or would you need to put a custom made steel or brass insert in the hole first?
As you can see on the image, there is still a bit of brazing solder left in the tube from the previous closing-off, which was not solid but just a little concave steel 'lid'

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I would make another concave lid and just (low temp) silver solder it back in. That way you still have the clearance and mechanical integrity.

You'd need a new lid.
You can cut a piece out of a tube with same diameter as the cutout. Brazing it in should be pretty straight forward for a framebuilder.

drøn: the clearance shall be maintained. I.e. I don't want to this to be a round tube again (it never was anyway).

ColnagoDaft: so, there is no chance of simply filling it all up with brazing solder?

That's not what I meant. I'll try to find a photo later.

Not too sure that either filling the voids with solder or adding a scalloped piece in to fill the gaps is going to increase the strength appreciably.

It was originally like that before, too.

drøn: the clearance shall be maintained. I.e. I don't want to this to be a round tube again (it never was anyway).

No: imagine placing a tube in the cutout, at right-angles to the bridge (like a cross) so you can mark the size and shape of the lid on the tube, before you cut it out.

Thanks scilly.
same principle as used in this chain stay: http://lh3.ggpht.com/_FT9fLZv0mMs/S5GGlu63qtI/AAAAAAAAADc/ASJ4QkcUYTs/s800/chainstays.jpeg

Ah, I misunderstood you: "with same diameter as the cutout" = I initally thought you mean the same diameter as the tube with the cutout.

Yes, that will work.

if its a bit of a beater you could fill it with chemical metal and then file to shape, paint, look just as good. wouldnt need to put any heat in the frame either and it will set like stone so probably have a bit of strength to it

Are those bridges meant to take any force anyway? I always thought they are just there to stabilize the rear triangle against flexing too much. i.e. more tensile stress than compressive stress? no?

Yes, braking forces.

If the welding lamp is coming out to play, I'd suggest fitting a new bridge in the right place, rather than tinkering with the existing one..

braking forces on a track frame?

the bridge is perfect as it is, no need to replace - as said, it always was like that (with a filed-out curve and a brazed-in lid), I just made it a bit deeper (by around 1mm).

Filing out from a solid piece of steel proved to be the simplest, as I could use the same halfround file.
This will now be silver-soldered in.

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That looks neat, just out of curiosity what make of frame is it?

Shaun

Unfortunately, it's unknown. No number or code on the bottom bracket,
just the info that it was sold at Tony Butterworth and the framebuilder was
from the Sheffield region.
It's a quite nice 531 frame with lovely t-rex dimensions (ST 60.5 c-c, TT 56.5 c-c)
and Zeus dropouts.

Doing it yourself?

Together with a (metalworker) friend, hoping to learn how to do it.

No, not on a track frame.
Your solution looks like it will be a success.

Good for you, and a neat fit - it's not rocket science. Once you've brazed up a few pieces you're well away.

Done!

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With tyre

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bang tidy