Stainless Steel Braze-ons

[robc02]

I am planning to add some brake cable braze-ons to the top tube of a steel (531) frame. My sweat must be especially corrosive, as I've previously had a cable guide on the top of the top tube rust through, and had stops on the side of the top tube become corroded. Presumably it starts with a small paint chip - easy to get with such a small and vulnerable part. (I also used to get a lot of corrosion on polished seat posts).

Initially the idea of stainless steel braze-ons seemed appealing, then I read about Interfacial Corrosion:

http://www.lucasmilhaupt.com/en-US/about/blog/2013/3/interfacial-corrosion
http://www.cupalloys.co.uk/help-me-choose/

If the stainless steel does not contain nickel, then nickel containing silver solder will prevent corrosion, but is very expensive and, apparently, does not flow very well:

http://www.cupalloys.co.uk/other-silver-solder/index.asp (449, about half way down page.)

So I am now wondering:

1. How likely is interfacial corrosion, given that the joint will be painted?
2. How likely is it that the stainless steel used for the braze-ons already contains nickel?
3. Is it all more trouble than its worth and should I just revert to plain old steel fittings and keep an eye on them?
4. Should I use full length cable and stainless cable clips? - I'm not that keen on this solution as sweat/rain/grit etc get tend to trapped between the cable and frame tube causing scuffing and, eventually, rust.

[531colin]

I have done this 2 ways. First time I ground cable stops from the head and plain shaft of M10 A2 stainless bolts ...lots of grinding! I got a framebuilder to braze them on.
Later I fabricated stops from (A2 stainless bolt heads) ......M6 cap head (I think) drilled out the Allen socket to take cable outer, drilled and slotted for the inner wire. Made a "base" from an M6 hex. head, silver soldered the drilled cap head to the base with high melting point, silver soldered the fabricated cable stop to the frame with low temperature.
Both worked faultlessly. I think i posted it years ago, will try to find it.....
http://forum.ctc.org.uk/viewtopic.php?f=1&t=72820

[Brucey]

1. How likely is interfacial corrosion, given that the joint will be painted?
2. How likely is it that the stainless steel used for the braze-ons already contains nickel?
3. Is it all more trouble than its worth and should I just revert to plain old steel fittings and keep an eye on them?
4. Should I use full length cable and stainless cable clips? - I'm not that keen on this solution as sweat/rain/grit etc get tend to trapped between the cable and frame tube causing scuffing and, eventually, rust.

1) well the paint presumably failed with your old braze-ons before they started to corrode.
2) Very likely. A crude test is that if it is essentially non-magnetic stainless steel, it is very likely to be a Nickel bearing stainless steel. There are exceptions to this but they are mostly not alloys in common use.
3) judgement call.
4) there are always crevices and places where cables can scuff, no matter how it is done.

In general terms if you think salt is causing corrosion then you probably need to wash your bike more often. Similarly if the paint is breached then you need to treat the area properly and touch the paint in before corrosion takes hold. If you also protect the braze-ones with something that inhibits corrosion (like waxoyl) then you ought to be able to make the braze-ons last well.

You can make some nice cable fittings using short lengths of 7mm OD, 5mm ID stainless steel tubing. These can be used as guides for full housing or (with stepped ferrules) a bare cable run between, as you wish.

If you use ordinary steel fittings then (provided the flux is removed properly) it ought to be the fitting that corrodes first. At least this can be replaced; by contrast if you use stainless fittings you may be concerned about interfacial corrosion but you ought to be at least as worried about bimetal corrosion whereby the steel tube corrodes through near the fitting, leaving the fitting untouched. To prevent such corrosion you need an intact paint and/or wax film over the interface.

cheers

[robc02]

Colin, I can see you went to some trouble to make those fittings! Was that because they weren't available commercially at the time, or because you had particular ideas about what you wanted?

I don't know enough about materials to know the composition of the bolts you used, and I don't suppose you know what filler rod the framebuilder used. I presume, though, that you haven't had corrosion problems.

Brucey: One of the bikes in question was a TT bike, being ridden hard, and subject to salt, for up to 2 hours followed by an hour or two drive home before washing with soap and water. (Usually I would also give the area a squirt of water and a quick wipe before driving home). I made a point of washing the seat post and top tube after each ride due to previous corrosion issues, but to little or no avail! Of course, I have no way of knowing how good the paint job was, but clearly it got damaged on the brake cable fittings (and also at the top of the seat lug). I suppose a modern powder coating might be tougher if done properly. I did regularly touch up the broken paint but it felt like a losing battle. The other bike to which I referred was a year round commuter/trainer and had a much harder life, so cleaning was only done weekly or thereabouts.

Initially my concern had been about dissimilar metals corrosion, but my brief research found no mention of this, only interfacial corrosion. How severe is the dissimilar metals problem likely to be? I certainly don't want to find that the frame tubes are corroding - even if the braze ons are still attached and in pristine condition!

[Brucey]

Initially my concern had been about dissimilar metals corrosion, but my brief research found no mention of this, only interfacial corrosion. How severe is the dissimilar metals problem likely to be? I certainly don't want to find that the frame tubes are corroding - even if the braze ons are still attached and in pristine condition!

it can be just as bad or worse. Often it is aided and abetted by flux residues around the braze-ons. Almost any brazed joint can suffer from it (because the braze metal rarely has the same potential as the other metals) but stainless steel is obviously going to be a bit worse, in the 'large cathode, small anode' type of localised attack.

On a utility bike there is much to be said for a black coloured finish and then using waxoyl round the fittings.

cheers

[ChrisButch]

In general terms if you think salt is causing corrosion then you probably need to wash your bike more often.

This is probably stating the obvious, but I think the reason corrosion in this area is such a common problem is that the risk is greatest in hot weather, when you sweat more, there's less wind to blow it away...but that's exactly the time when we're least likely to wash our bikes. There's no mud on the roads, the frame looks superficially clean, so cleaning is usually restricted to the transmission. Salt rapidly dries on the top tube and accumulates unnoticed.

[robc02]

This is probably stating the obvious, but I think the reason corrosion in this area is such a common problem is that the risk is greatest in hot weather, when you sweat more, there's less wind to blow it away...but that's exactly the time when we're least likely to wash our bikes. There's no mud on the roads, the frame looks superficially clean, so cleaning is usually restricted to the transmission. Salt rapidly dries on the top tube and accumulates unnoticed.

I think there's a lot in that, but in the case of the TT bike I referred to, it received regular washing. I can only suppose that the several hours of exposure to salt before washing is what did most of the damage. Maybe the washing, especially the post race "squirt and wipe" didn't remove the salt well enough.

[Brucey]

sometimes (when climbing, on the rollers etc) the sweat can drip down onto the top tube directly. But otherwise (esp on a race bike) I think sweat can get onto the top tube when you stop and the bike is between your legs.

In the latter case I think the middle braze-on (of three guides say) is likely to suffer most. That said, such corrosion is difficult to distinguish from that provoked by flux residues.

cheers

[robc02]

sometimes (when climbing, on the rollers etc) the sweat can drip down onto the top tube directly. But otherwise (esp on a race bike) I think sweat can get onto the top tube when you stop and the bike is between your legs.

Yes, and when riding, especially in a crouched position, sweat gets onto the seat post and the back of the top tube. I used to see clear salt stains on the seatpost and around the seat lug after a hard ride.

A bike that I currently ride has brazed on cable guides along the top tube. The rear one has corroded right through, the middle one is also corroded but salvageable. These guides are very thin and are in a vulnerable position. Unless the paint is very tough some chipping seems inevitable. It could be coincidence that the rear one has suffered most - maybe its paint was the first to get damaged. I originally wanted top tube guides and full length cables to overcome cable corrosion and eventual seizing in the run from the rear stop to the brake on previous bikes - all I did was to replace one problem with another!

I wonder whether more substantial stops (or guides) with fewer sharp edges would survive better - both because the paint might stay intact for longer and because there is more metal for the corrosion to get through. My Surly LHT has such fittings so I will probably find out in due course.

[Brucey]

....I wonder whether more substantial stops (or guides) with fewer sharp edges would survive better - both because the paint might stay intact for longer and because there is more metal for the corrosion to get through...

My suggestion of using short lengths of stainless steel tube was made with this in mind; it also gives you 'your choice of problem' in that you can have a bare cable or a full housing as you wish.

However what I wouldn't recommend is that you put a slot through tube of the specified dimensions; I think that would be a step too far unless you substituted thicker-walled tubing.

cheers

[robc02]

I quite like the idea of using stainless tube, though I can't find any 7mm OD at the moment. All I can see is 8mm or 5/16" OD.
I've just been reading up on machining stainless steel and it seems that Grade 303 can be turned and drilled on a mini lathe (I have an ancient Myford) so I might give that a try.
My first thought was to buy some from Ceeway, but they seem to have only a limited range in stainless.

[Brucey]

a suitable alternative might be 1/4" x 22 swg stainless tube (which is a standard hydraulic size, I think). However this leaves the bore a gnat's under 5mm and this means that not every flavour of cable housing will fit down the middle of it.

If you draw a blank on this or the 7mm let me know, I think I have some 7mm x 1mm stashed away somewhere (hey, guess why... )

If you fancy a simple (and wholly DIY) route you can make your own stops from 0.8mm stainless sheet, wrapped round a mandrel. The seam sits against the top tube, and is only joined when the stop/guide is brazed onto the frame.

For a bare wire installation, I'd suggest that you can use Jagwire cable ferrules; they are difficult to find but they have a fat alloy body (with a liner tube for smooth operation) and enough meat in them that you can turn a ~5mm long spigot into them any diameter from ~4mm to ~6.5mm. I've made some really nice custom ferrules by machining these to size.

cheers

[531colin]

Colin, I can see you went to some trouble to make those fittings! Was that because they weren't available commercially at the time, or because you had particular ideas about what you wanted?.............

I had forgotten how it all started.....more than 15 years ago ....my old Bob Jackson had brake cable stops on top of the top tube, with those daft little rings the cable goes through. I don't think paint stands much chance on corners and thin edges, and I sweated all over the top tube which then went rusty.....does this sound familiar?
That was the bike I first made stops from M10 bolts, I had Jacksons braze them on and respray. I don't think there is any rust there now.
Second bike I made similar stops and silver soldered them, then hand painted.
Third bike is the one I linked earlier where I fabricated cable stops from separate bits.
When I get some daylight I can do photos and check for rust, except the third bike which I broke up as it rode like a pig.
Stainless dropouts, fork crowns and lugs dont seem to be a problem for corrosion....even listing stainless cable stops...http://www.framebuilding.com/Braze%20ons.htm

[Manc33]

What about sanding the paint off the offending part and painting Hammerite back on?

Does that stuff really do anything at all to help keep rust away?

Years back my dad had a full steel frame (531) painted in Hammerite, but again like the above solder prices, its not cheap. If your frame is black its easy to just get a tiny tin to paint the part and around where it connects to the frame.

[robc02]

What about sanding the paint off the offending part and painting Hammerite back on?

The problem with this is that many of the fittings are so thin that there is very little metal to sand away. Mine are very similar to Art 104 on this page:
http://www.ceeway.com/Braze%20ons.htm. More substantial fittings will undoubtedly fare better.

If your frame is black its easy to just get a tiny tin to paint the part and around where it connects to the frame.

..one of the reasons why I have often chosen black frames! Though its getting a bit dull now so I might change to a different colour for this frame - I'll pick a RAL or other standard colour so that touch up paints can be bought.