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Weld/braze addition on steel fork - how much respray needed?

Posted: 17 Oct 2020, 3:31pm
by mikeymo
I was pondering having something welded onto my fork, a little metal addition. Or maybe brazed on. Roughly an inch in size.

How much paint gets burnt off by the heat of these processes? It'll be on the inside of one leg, about 6 inches up from the dropout. How far does the heat spread?

I'm wondering how much respraying/repainting I'll have to pay for or do.

Thanks.

Re: Weld/braze addition on steel fork - how much respray needed?

Posted: 17 Oct 2020, 3:41pm
by simonineaston
It may depend on who does the job... I had some canti bosses brazed on to fork legs by Argos and lost paint in the region of a 3cm dia circle.

Re: Weld/braze addition on steel fork - how much respray needed?

Posted: 17 Oct 2020, 3:46pm
by mikeymo
simonineaston wrote:It may depend on who does the job... I had some canti bosses brazed on to fork legs by Argos and lost paint in the region of a 3cm dia circle.


Thanks. That doesn't sound too bad then. Careful brushwork might produce an acceptable repaint.

And I wonder if brazing produces a larger damage area - doesn't it involve a gas torch, whereas if the welding is electric it's more local (can you tell I know nothing about these two processes?!)

Like you say, if it's somebody careful, who knows I don't want to do a full respray, they might take extra measures to protect the paint.

Cheers.

Re: Weld/braze addition on steel fork - how much respray needed?

Posted: 17 Oct 2020, 4:10pm
by tatanab
mikeymo wrote:And I wonder if brazing produces a larger damage area - doesn't it involve a gas torch, whereas if the welding is electric it's more local (can you tell I know nothing about these two processes?!)
"brazing" using silver solder is at about 600C. Gas welding about 3000 and arcy sparky about 6500. I'd say there is less potential for damage at the lower temperature. I have fitted good old fashioned lamp bracket bosses (big lumps of metal) with silver solder, no trouble. Bear in mind that you will strip the paint in the area to be worked anyway. I agree with simon that the damage area is likely to be about an inch.

Re: Weld/braze addition on steel fork - how much respray needed?

Posted: 17 Oct 2020, 4:22pm
by simonineaston
If it were me doing the work, I'd have no idea how to heat the work area, worry that the solder won't flow properly and so err on the side of caution, over-heating everything. Smoke will billow, the work-piece will over-heat, the workshop will catch on fire and everything will be destroyed - on the other hand, someone who knows what they are doing will only apply topical heat sufficient to do the job properly... :shock:

Re: Weld/braze addition on steel fork - how much respray needed?

Posted: 17 Oct 2020, 5:55pm
by DaveP
I don't think there is a "correct" answer to this - it all depends.
However, I did once have rack points brazed on to a frame, by a recognised frame builder. The heat affected zone (of paint) was something like an inch each way. I actually thought that was worth a respray - but you could call me fussy and get away with it!
Just ask the chap who's going to do the work. He probably has a fair idea of his typical outcomes, but don't ask for any sort of guarantee. Stuff happens...

As for a choice between welding and brazing - the metallurgical consequences are much more important than any damage to paintwork.

Re: Weld/braze addition on steel fork - how much respray needed?

Posted: 17 Oct 2020, 5:59pm
by fastpedaller
just paint the forks with black after the job's done - forks don't need to match :lol:

Re: Weld/braze addition on steel fork - how much respray needed?

Posted: 17 Oct 2020, 6:17pm
by mikeymo
fastpedaller wrote:just paint the forks with black after the job's done - forks don't need to match :lol:


What, not even each other? This is only one leg of the fork.

But you're probably right. I've got a half used tin of black hammerite somewhere. I might not even bother with a brush, just smear it on with a couple pages torn out of back issues of Cycling Today.

Re: Weld/braze addition on steel fork - how much respray needed?

Posted: 17 Oct 2020, 6:20pm
by peetee
Whether you should try this could very much depend on what steel the forks are made of. If for example you have a cro-moly tube set and a fork designed for disc brakes the chances are good that there is enough metal present that your localised heating will not compromise the integrity of the tube. However, if the bike is a feather-light road frame with 531c or 753 tubing that has seen a fair few years of all-year-round riding I would very much advice against it.

Re: Weld/braze addition on steel fork - how much respray needed?

Posted: 17 Oct 2020, 6:25pm
by mikeymo
peetee wrote:Whether you should try this could very much depend on what steel the forks are made of. If for example you have a cro-moly tube set and a fork designed for disc brakes the chances are good that there is enough metal present that your localised heating will not compromise the integrity of the tube. However, if the bike is a feather-light road frame with 531c or 753 tubing that has seen a fair few years of all-year-round riding I would very much advice against it.


Ridgeback touring bike. Reynolds 520 fork, canti brakes. It's tapped for low rider front racks, so I assume/hope that the combination of designed for touring/front racks mean that the fork was designed to be reasonably robust. Very little use and not that old.

Cheers.

Re: Weld/braze addition on steel fork - how much respray needed?

Posted: 17 Oct 2020, 6:29pm
by peetee
Could the rack braze on be utilised with the addition of a screw-on plate? It’s a bit mysterious what you need this for :|

Re: Weld/braze addition on steel fork - how much respray needed?

Posted: 17 Oct 2020, 6:32pm
by Biospace
The difference between a skilled welder/solderer can be significant, with a bicycle frame this matters! There are products used which help minimise conduction of heat from the working area, preserving paint really well.

Heat spread isn't necessarily less just because fusion takes place at a lower temperature of one is does with a gas torch and the other electrically, typically penetration takes place so quickly with MiG welding that heat doesn't build up as much. It's worth asking about MiG brazing, the best of both worlds and not as rare as it once was now high and ultra-high strength steels are routinely used in motor vehicle construction.

The skill of the craftsman still probably matters most, just a shame practical skills are so under-valued in England today, as it's resulted in a huge shortage.

Re: Weld/braze addition on steel fork - how much respray needed?

Posted: 17 Oct 2020, 6:49pm
by 531colin
Who is doing the job?
The tubing is going to be around the 1mm wall thickness.....if you want it welded, your fitting should be a similar thickness, or you can hole the tubing before the fitting is up to temperature.
If you want a big lump of metal stuck on, go for silver or braze.