Help filling tiny gap

[James Riley]

I have a steel knife blade and a brass guard. The brass guard is a pretty good fit around most of the tang but it is not perfect. I was going to solder the brass to steel but before I start, I have a few questions:

1. Can I use the flux and solder that I use for my copper pipe plumbing?
2. If so, do you have any advice on filling the gap(s)? I'd guess the gaps are about 1/32" or so. I'm used to soldering copper pipe fittings that are snug. This is different.

Ideal would be a solder that looks like brass, and which I could "build up" a little bit (without messing with the steel temper) but I don't know if there is such an animal. I used to be a pretty good gas welder but that was 45 years ago, it was all steel to steel, and it definitely melted the parts to be joined. I don't think I want to do that to my blade.

Thanks for any advice/ideas.

Edited to add: I did some research and it looks like Braze Welding may do the trick. Unlike brazing, it doesn't rely on capilary action and allows for build up without actually welding (melting) the two metals. I guess my question would be, would the brass rod melt before my brass guard?

[f350ca]

Welcome James
Brazing brass is a touchy process, can be done but the brass is really close to the molten stage when the brazing wire is ready to flow.
Think it would be too hot a process for your tempered blade though.
There might be a silver solder alloy that would have a low enough flowing temperature for your application. I've never used the silver solders, more the silver brazing alloys that flow at too hot a temperature for your blade to survive. Thet contain some copper and polish out to a goldish colour that would blend into the brass guard.

[Dr Stan]

I highly recommend going to anvilfire.com and posting your question in the Guru's Den. Before I gave up blacksmithing due to numerous hand surgeries I was a member and the folks there are some of the most knowledgeable and helpful metal workers you'll ever find. Lots of knife makers on the forum so you should get some excellent advise.

[Hawkeye]

One major consideration for a knife blade will be the heat that you are using and how far into the blade it migrates. If you can keep it off the cutting edge, it shouldn't do too bad.

[Highpower]

(01-01-2021, 05:30 PM)f350ca Wrote: There might be a silver solder alloy that would have a low enough flowing temperature for your application.

Brownells makes a low temperature (475°F) silver solder that could work although it won't be brass colored.

Hi-Force 44 solder and #4 Comet flux.

Welcome to the forum James!

[Highpower]

(01-01-2021, 12:03 PM)James Riley Wrote: Edited to add: I did some research and it looks like Braze Welding may do the trick. Unlike brazing, it doesn't rely on capilary action and allows for build up without actually welding (melting) the two metals. I guess my question would be, would the brass rod melt before my brass guard?

It could be TIG brazed I suppose but it would require a careful application of heat to minimize the heat affected zone. Perhaps keeping the blade submersed in a container of water with the tang sticking out?  

I managed to get this stainless steel 'tea strainer' basket re-attached to its handles using very low amperage (5 or 6A) TIG brazing and small diameter silicon bronze wire. The basket is roughly the size of a golf ball. By comparison the larger filler rod seen below the basket would have required much more heat and would have resulted in melting the thin stainless parts instead.

[Dr Stan]

Something to consider is using a heat sink that covers a majority of the blade made from either aluminum or copper as both have much higher coefficients of conductivity than steel.