Questions about silver solder

[ltlvt]

I've seen people that braze carbide to steel for cutting tools using oxy-acet torch using regular brazing wire and flux. also have seen others that use silver solder. Some use pastes some use foil. I am soon going to be needing to join a hardened acme threaded rod to the cross-slide handle for my lathe. I've done a lot of regular brazing and also tig and stick welding in my past but not very educated on which silver solder to use and what temperatures it requires. I've seen quantities of paste on eBay and Amazon that are in syringes and mostly advertised for electronic work. I am assuming I need to stay away from this paste for the repair I need to make. How ever if I could use a map torch and good grade of silver solder, I think that would meet my needs. So what solder what paste what heat source and what kind of clearance (fit) do I need to make a good joint? Any experience on this subject will be greatly appreciated.

 

[Huub Buis]

I use 3% silver, 97% tin to soft solder HSS or steel, on steel. It melts at about 250°. It is the same solder that is used to solder copper in pluming (Netherlands). For flux I use S39, not the flux for brazing. After soldering, you need to wash the part using warm water to remove the flux.
It is not as strong as silver or copper brazed welds but strong enough for making a turning or milling cutter.

You could also use loctite to glue this handle on the acme threaded rod. Just as for soft soldering, the fit should be pretty loose so that the soft solder or glue can get between the rod and the handle.

 

[Ed ke6bnl]

I use the same silver solder used for refrigeration and flux.

 

[ChazzC]

Commercial brazed tooling is done with induction heating (IDY or $200 - $600 on Amazon)

 

[MrWhoopee]

What grade/how hard is that Acme threaded rod? If it were me, I would probably TIG it with stainless filler and call it a day.

 

[Nutfarmer]

Hard silver solder is what to use. Don’t remember the exact percentage silver , but over 50 percent. It uses a borax type flux like what is used with brazing rod. Don’t try to use regular solder flux. Don’t waste your time with so-called silver solder with only 5 percent silver. Clean and flux the parts to be silver soldered and heat like your would copper pipe. The silver will suck into the joint.

 

[ltlvt]

I use the same silver solder used for refrigeration and flux.

What are you using for heat. I tried that today with Map and no success getting it to flow

 

[ltlvt]

What grade/how hard is that Acme threaded rod? If it were me, I would probably TIG it with stainless filler and call it a day.

4140 pre hard don't know the rockwell If I still had argon I would but also took my argon bottle back to Airgas

 

[benmychree]

I use the same silver solder used for refrigeration and flux.

I agree, that would be 18% silver, balance copper, with paste flux, (borax) oxy acetylene, with just enough clearance to slip fit.

 

[whitmore]

I use the same silver solder used for refrigeration and flux.

Around here, refrigeration typically uses sil-fos (a phosphorous doped silver solder) that flows for copper-to-copper
joints with no flux (presumably reducing flame).

Carbide is cobalt-binder with tungsten carbide grains, and getting a good cobalt-iron joint would probably
benefit from a different flux than used for refrigeration. But, I've only done silver soldering with jewelry
type supplies... the Real Welding Suppliers don't sell in small quantities.