I have decided my next frame should be a 29er (because I’m 6’4″ and my 26er looks like a bmx with the seat down) and I want it to be steel for a nice ride but with racey components/geometry so that I can race in local series etc. (but not be competitive, by any means). It would also be a bike I would take to trail centres and ride at places like cannock, whinlatter, dalby, glentress etc.

I can braze and am confident I could fillet braze a frame together, but is it going to be as strong as the TIG welding that everyone else seems to be doing?

I intend to copy either boardman 29er or charge cooker with 100mm travel (other suggestions welcome) geometry using (hopefully) 931 or some other stainless equivalent.

Also any welding/brazing buffs see any issues with brazing different alloys together? I intend to buy a bb shell and head tube that are stainless but not reynolds by any means.

TLDR: Fillet Braze = TIG in strength?

That’s going to take a lot of silver to make the fillets.

I would be using brass solder (with flux already wrapped around the rod) instead of silver solder due to the cost of the silver.

Not on stainless steel I’m afraid.

Well that would be my first mistake then, I haven’t seen anything flying around that is contrary to thoughts.

Another reason I was against TIG was because I do not have the ability to internally flush the tube with argon during welding. Any suggestions on that front if i do have to go with tig?

Y piece on the argon supply, hose into the frame tube, tape up all openings and then put in a few bleed holes and purge, argon is heavier than air, pretend you are trying to fill it with water and arrange bleed hole to suit.

Don’t use the flux-coated rods, they’re rubbish for bike stuff.

It is possible to fillet stainless steel with brass.

Braze can be just as strong as TIG, and possibly more fatigue-resistant (though that’s debatable).

You generally don’t need to purge internally with steel, unless you’re doing really posh alloys.

Shit man, stainless seems like a lot of effort, maybe ill go back to a standard steel and braze that then.

edit: BC – I did see you mention that on the thread that got me interested and researching it, even with stainless, its a bit of an alien alloy to me, I usually work with mild or 6061.

Unless you’re going to leave it unpainted – and spend months polishing it – then stainless has few benefits really.

From Cy(cotic)
“The main problem I found with 953 is that for MTB’s it’s not possible to get thick enough tubing (almost regardless of diameter) to take the loads a compact frame and 400mm seatpost + offroad riding put on a frame. The seat tube is where mine went, and I didn’t do another one because Reynolds can’t get material any thicker I was used on that frame. The head tube also suffers from this problem. All the other tubes were much lighter than their 853 counterparts on the Soul, and the whole frame weighed in at 3.7lbs for the large. Not quite Soda weight, but giggly light nonetheless. And it looked GORGEOUS. I’m not normally one for this kind of outpouring, but it is a lovely thing. It’s hanging up on the wall at the workshop in fact. The main drawback at the time was a lack of a cromo equivalent tubing in thicker walls to get around these problems. It was either crazy strong/thin/expensive 953, or 304 grade which is basically chemical pipe and is really weak. Shame though. I’d love to do something more with it. I should give Reynolds a call and find out where they are with it.

You’ll see road frames out there because it allows trad steel builders to build nearly ti weight frames without having to learn too much in the way of different manufacturing techniques. It works for those frames because the seat tube and head tube loads are that much lower that you can build lovely long lasting frames.”

I do intend to polish the crap out of it and leave it unpainted, was more the corrosion resistance I was keen on.

How about a clear powdercoat instead? Can look fantastic (and a bit more industrial / less pimpy than polished).

TIL – dont use stainless offroad, choose 853 and braze the shit out of it.

Max you should have known that stainless would be a nightmare to deal with!

Yeah I did nathan, but it is lovely when its finished!

I’m confused, are the hive saying that you can’t braze stainless?

It is possible to fillet stainless steel with brass.

I’m sure its possible, would you recommend it, I had assumed that you would have to get the material too hot and it would start to sugar.

Hotter than TIG would get it?

I do it quite a bit – it needs to be very clean, and you need to use the right flux and brazing alloy.

BC – could you recommend am alloy and flux? Or should I be looking at charts to figure that one out? the bottom bracket and head tube will not be reynolds.

Ben is definitely the man for stainless, and maybe also Matt at 18 bikes (see mtbr forum). Also have a look at Cycle designs rod and fluxes ($$$).

Why not just do a “feature” tube in polished stainless like the seat tube? Then do the rest in regular painted / powder coated steel for contrast? Bit less risky than super thin stainless top / down tubes. Or a stainless rear end (if you can sort the bends out).

I take it there are no issues with brazing the different alloyed tubes together then? My brazing knowledge is limited to automotive and zone application with things like dip sticks as opposed to frame tubes.

I like the feature tube idea, that is a definate option.

max and his overly ambitious framebuilding projects!

Steel is real oli!

Oli you can’t talk about ambitious frame projects!

😉

BC – could you recommend am alloy and flux?

Sifbronze 101 is beautiful for fillets, and I mostly use Cycle Designs flux pastes.

There’s no issue joining different steels, as you’re not melting the tubes – the brass is really just supergluing the tubes together.

This might be useful:-

http://forums.mtbr.com/frame-building/reynolds-921-a-888701.html