I should mention that I plan a full repainting of the frame, followed with an application of art. I already have the art and I plan to mix Rustoleum paint to achieve a close color match and then apply the paint with a brush (I prefer brush to rattle can spray)...

We'll have to agree to disagree on the brass (bronze) filler. Bronze may not be as strong as the steel, but you can use more of it to compensate. That's why a bronze fillet brazed frame is as just as strong as a lugged one.

Crack propagation is a study in fracture mechanics, a field that I haven't studied much, but what you're trying to do is remove stress risers. In many cases you actually want a softer material. I wouldn't fill this hole with brass, I'd make/machine a small plug and silver braze it in. That keeps the heat affected zone down to a minimum. Filling that large a hole with brass filler would take some skill.

I did something similar to this a few years ago on a vintage Falcon frame.




Defluxed, filed and sanded the outside. Luckily a new wrap around Falcon decal hid the repair and no repaint was needed.

But, again, odds are nothing will happen on the OP's frame if he leaves it alone and just rides it, however the odds of a crack propagating are much, much higher with the hole (my 2 examples I mentioned earlier, for example). Ride it or not - that's a personal decision. I'm not saying it's a bad choice to not fill it. Saying it won't crack is just guessing, however.

Quote:

Originally Posted by xiaoman1

IMO,
I would not use brazing (heat) for a repair such as this. ..you may find that drilling the holes left a burr or high point around the hole, filing it or dimpling it will provide some "extra" hold for the filler. If you do not do this there is no way the Bondo will a stay in place when sanding the filler down. etc.
Find a small peening hammer or pick/scribe and just barley dimple the hole to allow for a thin layer of filler to adhere to the frame.
If this seems too drastic a solution (SMALL dimple), then I would find a suitable sticker or reflective tape and move on, watch for stress fracture (not likely) and it they occur us the more aggressive solution.
Best, Ben

I agree that bondo is not structural and I do think that the holes are going to compromise the frame .....so an "extremely" small dimple will provide enough area to allow the filler to adhere without applying a backer. If careful when applying the filler very little filler will be required and touch up of the paint will be minimal......been there, done that.
If you think the holes will lead to a catastrophic failure of the frame then welding/brazing is the only way to go....lots of paint damage to the tube and a lot of paint work to look forward to.
To my eye, adding more decals where they shouldn't be will just draw more attention to the area in question a small touch up will soon be forgotten.
Again,,to me, KISITB
Best, Ben

tough call, in the late 40's and 50's this was not an uncommon cable port, albeit with a brazed on bezel.
Silver will "stick" to chrome. one could silver on a bezel, then repaint.
if the vents to the headset and or seat tube are big enough, a roofing "tack" might be slid inside point out and epoxy welded as a backer, then fill with more weld and grind/file back.

last would be a small section of sheet silver, cut to an oval and formed to fit the tube, bonded in place then filed a bit of an angled port, polish it up.

Then why just not braze in a steel rod? And fillet brazing works because of the cross-section of material, not a thin layer of soft material. Hence the "fillet".

I am a frame builder. I have (stupidly) drilled holes in thin gauge top tubes and even brazed a reinforcement washer around it. After a while, it cracked. I am glad to hear that you are doing something, because once it cracks, you are looking at a top tube replacement/ say goodbye to your chrome. I have pulled out and filled in my share if misplaced waterbottle cage receiving nuts. Do not plan to fill in entirely with brass. Brass does not work well filling a 1/4" hole. I take a drywall screw, cut the threads off. put the screw cap in the hole and braze it in. Next, you just grind/ file and then sand it down.

Sure, why not? Brass is just easier to work with. From a practical point of view, when I'm filing and sanding the excess you want the filler erosion to be faster than the steel tube. I don't want to cut into the steel any more than I have to. Harder to tell when you're filing steel on steel.

As you're alluding to, strength comes from the properties of the material, as well as mechanics of solids (shape and size). You can make something stronger by using stronger material, or more of a weaker one. My patch is > thickness than the base material (tubing wall thickness), so, yea, I've got a bigger cross-section as well, per plan.

Someone put a hole in that tube. Not sure anyone would agree that this doesn't make the frame weaker. You've seen many frames drilled out in the same manner without issue. I've seen 2 where it eventually cracked the frame. Here's a third (maybe you missed this one).

I often put holes in the bottom of the down tube to run a wire from a front hub generator to a tail light. I always silver braze on some material first (often a very small washer) to reinforce the area around the hole. It's probably stronger than before.

The OP's frame has a hole drilled into it without any reinforcement. It's got to be weaker at that point, can be a stress riser location, and a place for moisture to intrude into the frame, especially at a place where sweat is dripping down from the rider (I'm sure you've seen many frames with rusted out top tube cable guides prove out that point). Maybe the frame will be just fine, maybe not. It's just bad practice to drill holes in frame tubing without reinforcement.

Since the OP's repainting himself (I'd bet for less than $1000), I'd get it plugged first.