Silver Solder Torch Selection

[Danuzzo]

Thank you for your replies. Good to know that the discoloration is normal. Also, appreciate the tips and the links provided for silver brazing. I guess I got lucky on my first try, as far as strength of the join goes. Attached are some photos (sorry about the poor quality), and criticism (not as to the photos) is welcome. I did try some light sanding on it. Need to do more research on the "acid" stuff.

In any event, I should explain what I used. Bernzomatic 8000 torch with propane, although it will use mapp pro as well; Harris 56 silver solder, and the Harris white flux. I did use "fire brick" as a base and surround. The 2 pieces I brazed together were of some turning scraps I had laying around:

1. Base made of mild steel, almost 1" diameter at top flange, about .200" thick with base of about .650" diameter and total height of about .650". Base had a slight shallow hole, more like a countersink on top where I placed part #2. I fluxed the hole.

2. This was a small piece of mild steel abut .320" diameter x about .250" long with a little nipple on top from parting on the lathe that I ground a slight taper to fit in the hole (countersink) of part #1.

 

[Steamchick]

All journeys start with the first small step...
Enjoy! (I do).
K2

 

[Steamchick]

May I suggest... you make a small crankshaft from whatever bar stock you have, silver solder it, clean it up for examination, bend it and bash it to destruction - or distorted to a point the joints are proven to be strong - then cut through in various ways to prove penetration of the silver solder? It can be quite an enjoyable experience finding that the solder went everywhere it should. - Or a learning experience if you find some faults?
It's what I was taught as an apprentice - and passed that test!
Later I did the same in college, and in production (daily checks) in manufacturing.
I wonder how many hobby "engineers" do that sort of thing?

I recall a job where I was managing a small production shop (about a dozen welders), so had to interview new welders, and get them through the testing before they could have a job. It was aluminium MIG welding. I inspected the welds after they were made, and again after they were destroyed and sectioned. I passed and failed people for their competence (to documented standards). But the foreman would not let me weld ANYTHING because I employed certified guys to do that! (I was not certified for welding!).
K2

 

[The Ignoble Troll]

Is T-cut just Rouge? - Will that work as a solder anti-flux?

I always just left on tripoli as an anti flux, or rouge.

 

[The Ignoble Troll]

From my limited experience with silver soldering steel parts together with high-temperature silver solder, there is a bit of an art to getting the two (or more) pieces hot enough to flow the silver solder, without overheating the flux at the joint line.
The thing that really needs to happen (in my opinion) is that the pieces (complete pieces, not just edges of the pieces) need to get to the right temperature to completely flow the silver solder all the way through the joint.
It is very easy to make a good looking superficial silver solder joint, but a few whacks with a hammer on a test piece will tell the tale.
For a high-strength connection, you need a very thin joint, and a completely flowed joint.

As I mentioned, I use any oxy-acetylene torch, and while that may be overkill for hobby work, it should be noted that there are a wide variety of tips available with an oxy-act torch, to provide anywhere from pinpoint heat, to very wide flames.
You can also use various sized tips, for large or small projects.
And by adjusting the regulators, you can dial in the heat you need for the particular application.
There is no downside in my opinion to having excess heating capablilty, since it is like the accelerator pedal in your car; nobody says you have push the pedal completely down when you use a car, and controlling the excess power is easy.

From a cost standpoint, the least expensive equipment that will do the job at hand makes sense.
If you have an overlap of other repair types in your shop, then the least expensive option is the one that will do all the types of repair you want to do, not just model work.

A very hot flame that is too localized/pinpointed will just burn hot spots on the metal pieces without getting the overall pieces hot enough for a complete flow.
The approach for silver soldering is the opposite of gas welding.
With gas welding, you want a narrow tip that concentrates all of the heat into a very small area, where you create a puddle and sort of pull/walk it along around the joint. The joint should be V-cut so that you are assured of complete and full weld penetration.

For silver soldering, you are trying to bring up the temperature of all of the pieces to a uniform temperature that is hot enough to get complete joint flow, but cool enough to not burn off the flux.
The joint is typically two flat surfaces that are separated by a very small distance, with the separation often obtained by using slight punch marks across the faces of the joint.
The brown flux helps with avoiding flux burnoff, since it has a higher temperature rating.

You don't want to pinpoint high concentrations of heat or temperature into a small spot when trying to silver solder.
Focusing high temperatures on the joint itself just burns off the flux and ruins the connection.

Try some test pieces, break/cut them apart to verify full penetration, and I think you will get the hang of it quickly.
.

Agreed. Good post.