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Re: Going to try brazing...

Posted: 8 Apr 2011, 2:19pm
by simonineaston
531colin wrote: I would hesitate to weld something myself if my life might depend on it being bike stuff!

Yes, that's why I decided just to stick to the 'cosmetic' stuff, like cable guides and bottle cage bosses. If I get on OK with these little pieces, I'll try making the racks for my ancient Moulton Safari look-a-like. I'm really looking forward to it, now I've heard from you folks and deduced it's worth having a go - I'll probably try to get some decent kit from ebay - Rothenberger? and sell it on when the obsession is over ( and I've moved on to bread-making!)
I remember I did try brazing as part of a college course years ago, but of course I was able to enjoy the use of all the college kit, which included brazing hearths, piped gas on-tap and wot-not. :D

Re: Going to try brazing...

Posted: 11 Apr 2011, 10:19am
by Father Jack
Can find out about helicopter, dad has syndicate group putting in costs for heli and plane.

Re: Going to try brazing...

Posted: 29 Mar 2012, 7:04pm
by Brucey
yakdiver wrote:Forget brazing and go for a small mig welder, with a special flux-coated wire that produces it's own gas shroud as it burns.

bit late now I know but.... Gasless MIG?

horrible horrible horrible horrible and poisonous.

The wire is flux-cored. In theory this ought to be no worse than flux-shielded arc welding, but in practice it ain't. To get the arc stability anywhere near good enough (I was told) they lace this stuff with Barium, which winds up as Barium carbonate after welding, which (unlike other barium salts which are insoluble and therefore fairly benign) is soluble in mild acid (like stomach acid) , so you can poison yourself with this breathe it in then swallow it.... It is also rubbish to work with, (very difficult in thin sections) usually gives welds with rubbish properties, has a very low deposition efficiency, goes rusty double-quick on the spool, and costs a fortune (x4 for a lb of wire, from which you get about 6oz of weld metal tops, generally more like four..).

The only things it has going for it is that you can weld out of doors in a howling gale and you don't need a gas bottle.

A machine that will only take 'gasless' wires is a false economy, no matter how cheap it is. By all means keep a reel for emergencies if you run out of gas or must weld in that howling gale, but otherwise stick to gas MIG where possible.

And for bike frames; last-gasp repairs and fabrication of gas-pipe specials using MIG is fine, but everything else is better done other ways.


Re: Going to try brazing...

Posted: 30 Apr 2020, 6:01pm
by 531colin
I'm resurrecting this old thread because I've stumbled on a couple of things which have amused me.
First off, if you want to join 2 tubes like this...

You can shape a grindstone like this...

using an industrial diamond tool (made for re-shaping worn grindstones)
and Johnson Matthey produce a solder called silverflo 40 which is a good gap-filler and will quite easily produce a fillet like this ( that's un-filed, un-brushed; just the flux dissolved in caustic soda)

(I bought the solder from "Solder Connection")
Better photos here...... bottom of page 3!

Re: Going to try brazing...

Posted: 30 Apr 2020, 6:36pm
by simonineaston
Fantastic! I didn't realize that the choice of solder could be so significant. :-)

Re: Going to try brazing...

Posted: 30 Apr 2020, 9:55pm
by hayers
Just to add my 2p worth - apologies if I missed these suggestions earlier in the thread:

Bits can be had from ceeway

I use silver solder from cup alloys 55 or 35% silver - the former flows nicely, latter fills gaps better. I use their EF flux for both.

For heating a seivert torch and 5kg propane bottle works for me and is the model engineer's favourite for miniature boiler making.

There's a book by Marc-Andre Chinonas easily available called "lugged bicycle frame construction" with a reasonable overview of building a frame with step by step pictures, including the braze ons. I have done some thjngs differently but nice to see an approach that works.

I would ignore his suggestion of homemade / adapted oxygen kit - if you want to use gas-oxygen I would definitely buy proper kit - and learn how to use it.

A decent propane torch will behave like the mapp torch he describes, but a decent sized burner will do lugged joints unaided.

Silver brazing (silver solder) done right is fine for all joints - some tubesets (eg Reynolds 953 i yhink) can only be joined that way - brazing or welding overheats them.

Good luck and show us some pictures!

Re: Going to try brazing...

Posted: 1 May 2020, 1:25am
by Brucey
simonineaston wrote:Fantastic! I didn't realize that the choice of solder could be so significant. :-)

There are (literally) dozens of silver braze chemistries, varying from ones which melt abruptly and 'wick into' narrow, controlled gaps like quicksilver, all the way to chemistries which allow fillets to be formed. Somewhere I have an old copy the JM master catalogue and that has (literally) hundreds of different alloys listed in it, each of which would have been developed for a specific application.

The characteristics which allow fillet formation include that the braze metal has an extended 'mushy range'. I.e. there is a range of temperatures in which both solid and liquid exist (imagine a metallic slush puppie; like that). This contrasts with the low temperature silver braze metals that you might use with a lugged joint, which have a very narrow melting range; they are either fully solid or fully liquid.

FWIW I have added braze-ons to several frames using nothing more sophisticated than a paraffin blowtorch and some carefully chosen materials. Using a filler material that allows small fillets to be formed seems like a good idea with things like canti braze-ons, even though the flow temperature is likely to be slightly higher . I've never worked with materials like the ones that Colin has used; it rapidly gets expensive to use silver-based consumables for making large fillets. If you are doing much of this sort of work then spending a bit more on a hotter gas torch allows you to use cheaper 'bronze-welding' consumables.

FWIW the alloys with the lowest melting temperature are often what are known as 'quaternary eutectics'; the low melting point is obtained at a specific composition; if the composition varies even a tiny amount so does the melting point. This is what makes these alloys difficult to work with, and is part of the reason why Reynolds 753 required special certification. In extremis, the braze alloy will melt, flow and then solidify, all without the temperature varying; the alloy changes composition enough when it melts (there is always some dissolution of the underlying material into the braze material, and also volatile elements in the braze metal are lost) that it melts then solidifies. This also means that the rework temperature of low melting point alloys is always significantly higher than the initial flow temperature, which again has consequences for the quality of the work.

I like the 'shaped grindstone' approach; however the fit can be made 'good enough' for a joint with a generous fillet radius, using an angle grinder. You do need to be good with the grinder though.


Re: Going to try brazing...

Posted: 1 May 2020, 2:16am
Brazing and silver solder is easy enough.
But I would go one further and get a bit of tuition (well that's not doable just now) perhaps videos online.

Being taught the basics goes a long way to satisfaction of the job.
I do more wood work than metal today and never regret my school woodwork classes.
Metal was what I wanted to do and did two years at school before going into mechanical engineering.

Braze welding is where you want to be unless its small fiddly stuff like braze ons.
For tubes that is, I imagine that the method Brucey describes works here as you play the torch back and forth and the filler rod is used to push the pool up then it solidifies to form that distinctive weld of bronze :)