Brazing question

[Justin King]

I have a piece in progress with an all-steel grip and a seperate steel guard, with a hidden tang (yes, I know that I am not sane), the grip and guard of which I would like to solder together with hard silver solder (high temp). In order to keep everything aligned during soldering, I have a mock tang that will be inserted in place while making the joint. I need a way to keep the solder from flowing onto the mock tang and soldering it into the grip, I need to remove it afterwards.

Question:
Does anti-flux work for the high temperatures used for brazing/hard soldering? And does it require a thick build up on the surface in order to work properly? There is pretty minimal clearance between the tang and the inside of the grip, so not much room to coat the surfaces without it being scraped off during assembly.

Is there another trick to keeping the solder from tinning on the tang and other areas where it isn't wanted? I though of just putting a layer of oxides on it by heating it up, but the flux does a good job of eating through it, just like it's supposed to.

Besides anti-scale compound, is there another trick to keeping the scale to a minimum during brazing?

 

[Mark Behnke]

Her's some good info, not sure if answers your?
Stacy will no doubt have the info you need.

 

[Bill DeShivs]

Dirt. If you can get a good, even coating of pencil lead on it, the solder won't stick.

 

[Justin King]

I knew about the pencil trick but have only used it with low-temp applications. After doing some test/practice joints yesterday, I'm second guessing the whole idea. I broke a test joint and found some porous areas in the interior, one of which was filled with black stuff that was probably flux, which is not good. I am also doubting that my MAPP torch is capable of heating the joint area with the added heat sink of the mock tang inside, so it may be a bust.

 

[Stacy E. Apelt - Bladesmith]

Pretty much any material that will not melt or burn at the soldering/brazing temps will work.
Yellow ocher is the industry standard. Mix it with alcohol or water and paint it on the surface you don't want the solder to fuse. Pencil lead will work, but starts to vaporize at 1250°F. There is probably enough clay in the pencil lead to keep the joint from fusing.