Is it possible to silver braze a 100mm (0.7mm) sleeve over a stainless seattube (31.7x 0.5) ?
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Sounds a bit ambitious to me ,if itās a tight fit you may end up with uneven silver penetration.
Maybe with a few holes to feed silver through?that could be either decorative or filled up during the process.
Yes you can. Heat control is key and an easy sliding fit.
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Hei @Thunderstang. I planing to do little bit the same. i want wo braze a 105mm gusset over my seattube. After i want to braze the toptube and the seatstays with brass on itā¦ do you know if itās possible? maybe @DEVLINCC knows also the right answer for this question?
and did you braze the sleeve? whats the most difficult steps in this process?
I only used silver on the fillets, 56% for the sleeve and 32% for the fillets. The fillets are far enough from the edge that the silver that melts underneath is contained.
You could do as Walt suggested and tack the edge of the sleeve with silver to hold it in place, do your fillet braze in bronze and then feed in some 56 from each end of the sleeve. Youāll get enough surface area wetted out to form a strong enough joint.
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The welding/brazing of the toptube and seatstays is more than enough to lock the sleeve onto the underlying seat tube, so you donāt need to worry about it structurally. You can just put a little silver in the top and bottom.
If you really want silver through the whole joint Iād drill a few small (like 1/16" or so) holes at various points to use to feed silver. Getting the whole joint to flow from one end, while theoretically possible, is going to be really hard to pull off.
-Walt
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Thanks a lot for the informations! Lot of nice inspiration for me. I think thatās the way how it works.
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Another question about brazing seat tube sleeve.
Is the roughness of the surface to be brazed important?
Sanding, sandblasting or smoothing?
(I only brazed a test piece, but that was not successful)
Martin
Roughness is definitely important for brazing. I sand surfaces with 80 grit emery cloth. Creating a āgrainā by sanding in the direction you want the metal to flow is also possibly beneficial, according to a lugged builder I know whoās in his 70s.
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If you have a lathe you could make a stepped extension instead of a sleeve. This will be much easier to braze with full penetration.
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The āgrainā of teh sanding can help direct flow but so long as the surface is bright and clean it will bond. bright being fresh metal with no oxidising.
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I plan to solder the top tube today. i wonder if it is a problem that the flux burns under the sleeve?
How did the sleeve go?
My ST sleeves are generally around 3-1/2" or longer with the point. I havenāt ever tried a sleeve over stainless though. I have done lugs and crowns in stainless and itās VERY easy to overheat. It goes from not quite hot enough to ādamn, now I have to start overā in the blink of an eye.
If I remember correctly, Steve Garro only flows filler about an inch into the sleeve, not all the way through.
Post up pics! Good luck!
anyone experience in brazing a sleeve with nickel silver?
I tried once with lugs - because I misunderstood. 
My technique at the time was not great, I received advice to use Nickel Silver flux and so, I assumed I should also use Nickel Silver. It was my first attempt at lugs and it went horribly wrong. I went back for more advice and figured it out but havenāt tried sleeves with nickel since.
I always use 56% and flow it all the way through the sleeve. My understanding is that really you just need to get the filler to go about an inch down into the sleeve from each end if youāre using a standard 0.6mm ST wall at the top and then adding a say a 1.5mm walled sleeve. That seems like it would be possible with Nickel Silver. I would question why but, Iām sure you have reasons.
The extra strength of nickel would be wasted on this type of joint. Brass or 56 is much easier to work with and very strong in lap joint. 56 is also a lot more expensive so thereās that.