capnjonny 

I am preparing to paint an old French bike frame and it is in great condition except for a small dent in the top tube. The dent is about 1/4" deep and 1/4" round . It looks like someone shot a ball bearing at it. I want to fill the dent before I paint the bike. All I have is this one small dent. As a possible alternative to bondo I thought maybe I could fill it with solder and file it smooth. I have already sand blasted the frame so it is perfectly clean.

Is this a good idea. I remember people used to fill seams with lead back in the 50's hot rod days. If I used electrical solder would that work or do I need to use plain solder and flux.

Is there a best way to go about this. I don't want the bondo or solder poping off at some later date.

Any suggestions appreciated.

aggiegrads

Solder is a good idea, but brazing rod would be better, and I would say you definitely need flux either way. I am sure that a frame builder could do it in five minutes if you throw them a 20, and would probably give you a short strip of sandpaper to help smooth the surface.

dedhed

If you plan on powder coat, you must braze fill and file/sand smooth

DaveSSS 

Unless the frame is being powder coated, bondo is the way to go. Brazing would take some very careful filing and sanding, to not show.

Moe Zhoost

I've used both brazing rod and lead. Brazing rod is harder and more durable but takes a bit more work to finish. Lead solder does work great for small areas, but @dedhed is on the money about powder coating. The curing temps could be above the melting point of the solder, depending on what you use. Plumbing solder is typically 50/50 lead/tin with a low melting point. Auto body lead is something like 70/30 with a higher melting temp. That may be ok for powder coating, but no guarantees. Don't use electrical solder.

Neither lead or bondo will pop off if you apply correctly.

Good luck.

WizardOfBoz

As a bit of possibly useless information, soldering and brazing are essentially the same, except for the technical differentiation: In brazing the metal that you bond the surfaces with melts at greater than 450°C, and for soldering, less than 450°C. A lot of structural (like for radiator repair) solders melt in the 260-425° C range. Powercoating cure temps are in the 300-425°C range.

Seems to me that it breaks down: if you powdercoat, fill with braze. Else, use Bondo or solder. Given that this is expressly what Bondo is for, and its easier to apply than solder, that's what I'd use for painting.

carlosponti

not sure how feasible it is in your situation but

delbiker1 

I have a steel frame that had a dent in the front of the head tube, about a nickle size and maybe 1/4 inch deep. When I rebuilt the bike I took it down to bare metal and sanded it out to 1800 grit sandpaper. I had the frame powder coated and the powder alone nearly filled in the dent. At a close inspection, the dent can still be seen as a minor imperfection. At a further distance, unless you look really hard, it does not show.The powder coating is very durable and the color options are more than 6,000. Single stage is around $100. I had a 2 stage, special order powder used and it was $180.

ljsense

There are a few problems with solder. Unless you are experienced with it, it's hard to build it up into a nice smooth lump over the dent you want to cover -- it wants to spread out and coat the heated metal. That's why it's so nice for joining pipes -- it gets pulled into cracks. So I could see a frustrating experience as the solder doesn't take the shape you want it to. It could be cooling into all sorts of nasty lumps and pits, then fall off the frame and through the hole in your Croc when you heat it up too much.

Second, as others mentioned, anything you can melt with a Home Depot propane torch is not going to stand up to powder coating. I think that most powercoat ovens go to about 390 F or 200 C to cure for about 10-15 minutes. As others mentioned, that will be too hot.

Silver brazing is usually done with an oxyacetylene torch. If you find someone with one of those who will fill the dent for $20, also buy a lottery ticket. I always hear these legends of people with expensive tools and mechanical expertise willing to take on small jobs for a few bucks, but where they are, I don't know.

There are high temp epoxies that would probably fare fine in a powdercoat oven -- but I'd check with your powdercoater first.

If you're not powder coating, then I'd go with an epoxy. It doesn't absorb water and is stronger than Bondo. You could get the stuff you can kneed and apply like clay, then sand smooth.

Mad Honk 

There are a few problems with epoxy and those are about the cure temps and the breakdown temps. 350* is the best number you can find, and that won;t work for powder coating. Everything you want to do should be done with a frame builder on site for you. Some paints will accept bondo and others won't, find painter who knows his bizniz and trust him/her. It shouldn't be a problem. Smiles, MH

WizardOfBoz

Would the powder even stick to non-conductive epoxy?

ljsense

That's a good question. Static cling is what holds the powder on. I've seen powder coaters work with non metal objects, but I think it's more of a pain to make sure the powder is covering the object.

wsteve464

High temp epoxy good for 500 deg

https://www.amazon.com/Permatex-8433.../dp/B00O7NBVQ8

squirtdad

Home depot mapp torches will melt bronze. I have used them to remove cable braze ons

another option is for @capnjonny to call or go to https://www.silvacycles.com/ and see what it would cost for them to fill....then he could do the filing sanding

bunch of local references there Silvas is in Campbell CA and i know the Capn lives close

dedhed

Non conductive materials can be powder coated by preheating, but the material still needs to be able to take the high temperatures.

There is also UV cured powder coating that doesn't require heat curing but I believe needs the static part.

Both methods require more $$$$

xiaoman1 

O.P.
I believe that "Rolling Blocks" will still leave a small indentation because the impression either needs to be "pulled" out or "pushed" out from the back....I have never seen a dent that was rolled out that did not leave some small impression after rolling...the video still shows a dent after "rolling"so as other have said unless powder coating bond is the way to go.
The dent is small I vote for Bondo less work no heat and no filing etc.
JMO, Ben
Best, Ben

Loose Chain

I would just use a mild abrasive plastic/clear coat polish like PlastX. Buff it gently and then work outward into the unaffected area. Follow up with pure Carnuba yellow wax, call it good.

Moe Zhoost

I've used rolling blocks for dents. They definitely reduce any tubing deformation around the dent, but they won't return the tube to pristine condition.

Gresp15C

How about a small fillet from a welder, then file it smooth?

WGB 

Some people aren't bothered by dents.

Owner thought it was fine....

Saw this either Tuesday or Wednesday in Barcelona.