using silver solder

[ChainsawMan]

I have used silver-solder paste with NO success. I spread the paste in between the two pieces, then heat the two with Mapp gas. Obviously this is wrong. Why? And what is right?

 

[Alan Molstad]

Darn, I really wished that would have worked too...LOL

I hate to solder...50% of my soldering needs to be done once again.

But when I do it right, I am so darn glad that step is over!
I just use normal low-temp silver solder and staybrite flux.

One trick I have learned,
(Oh I have been told tons of soldering tricks, but this is the only one so far i have found worked for me)
, is to use a small brass rod that I have sharpened a bit . I run the point of the brass rod in the hot fresh solder joint to smear-fill any gaps.

 

[JCaswell]

There are numerous things that can spike your soldering jobs. One is using the wrong process, flux and/or solder for a given material. (Stainless requires different handling than sterling silver, for example.)

Without knowing what you're doing, I can simply generalize that the biggest problem folks run into when trying to silver solder is in neglecting cleanliness of the parts. You should pickle your parts in an appropriate solution (usually acidic). Sparex is a brand of a common one. This is less important with regular steel compared with non-ferrous materials, but things still need to be very, very clean.
Next is flux. The flux must match the temperature range of the solder.
If you're using paste and having trouble, you're probably blasting the joint from the top with your flame. This cooks/destroys your flux before the metal is to the appropriate temperature and it dirties the joint with fouled flux/solder residue. There is virtually no chance of success doing it this way.
You really need to heat the part indirectly and very quickly, which means Mapp might not be hot enough depending upon what you're soldering and the temperature range of your flux and solder.
Paste is often used in kiln soldering rather than torch, though I've done it with torch. (I prefer NOT using paste).
In short, I suspect your problem is probably exposing the paste to the open flame and cooking the heck out of it. Try heating fast and from underneath, if possible, and stop when the solder flows. Don't boil it.

 

[Alan Molstad]

My brass guards go all the way around the tang.
Now dont tell anyone, but the last few knives I have started to just wrap the whole joint 2 times around with solder wire before I start to heat things up.

When it gets hot and melts, I just use the short pointed brass rod I was talking about to push the solder wire down into the heated joint.

Most of my problems are the basic ones.
Too much heat
Too little heat on the other side
Dirty joints
Dirty solder paste, (I dropped that stuff)
and,,,,,,,gaps.

 

[JCaswell]

The fit should be really good--no visible gaps.
I use a sharpened piece of stainless welding rod (about 1/16), dip it in the liquid flux and touch the point to the joint (the top side). A drop or so capillaries it's way into the joint. I'll heat from underneath and touch the fine solder wire to the joint periodically. All of a sudden it flows and zips around the joint. That's it, no more heat. Very fast. Maybe 1/4 to 3/8 of solder wire used. Very little or no cleanup.
You don't need to flood the solder in. It makes it all around fast and easy.

Naturally, if the fit stinks to begin with and you're parts are dirty, you'll have trouble. This is one of those areas where several things have to be right and there's just no getting around it.

Good luck!

 

[Alan Molstad]

The fit should be really good--no visible gaps.
!

rightttttt.......

Now, how would you fill a gap you could drop a dime in?...LOL

 

[Stacy E. Apelt - Bladesmith]

Soldering is divided into two types (for knife making purposes) SOFT soldering and HARD soldering.Most soft solders flow at around 400F, hard solders at around 1100F.Soft soldering is what is done to guards and such. FORGET paste solders. Get a low temp solder that is alloyed for your purpose. Either TIX or Stay Brite are the most common ones. Get the flux made for that solder.As said start with clean (Really clean) parts that are as tight a fit as you can make. Solder is not a filler,so avoid large gaps.Clean everything with denatured alcohol prior to soldering.Here is a guard soldering primer:
After setting the guard in position, place the blade in a vise (pad the jaws if needed) with the tang upward.Apply a liberal amount of flux around the joint area. Wipe excess flux from blade where it runs down.Take a torch with a SMALL flame. Those rechargeable butane "hobby" jobs are perfect.THE ENEMY OF A GOOD SOLDER JOB IS TOO MUCH HEAT!!. Heat slowly from the blade side of the guard. heating the guard and blade evenly.As the flux runs and bubbles start wiping the end of a piece of solder along the joint when it starts melting remove heat from the blade.apply a small amount of additional flux to the joint, reapply heat and start wiping the joint with the solder. As you wipe the solder along the joint it should flow smoothly and run along the joint. Use only a small amount of solder.Once some has flown along the joint stop adding more solder. Use a solder pick (Sharpened 1/8" brass rod ) to scrape along the joint and make the solder run smoothly.The heat is removed whenever the solder is flowing, and only reapplied when it starts to harden.Let cool down for a minute or two. Take the blade out of the vise and put a coil spring on the tang. Place the tang in the vise with the spring slightly compressed against the guard back. Look at the solder joint at the ricasso.If it is smooth and shiny, you did good. If it has gaps or is blobbed with solder that tells you there was not a clean joint, too much heat, too much solder, etc. Apply flux.Take the flame and slowly bring the joint up to the flow point again,running the solder pick along the joint to flow smoothly around.Wipe off excess solder with a damp paper towel while it is liquid.Try to avoid adding solder from the blade side .With experience you will be able to do the whole job from the blade up position, applying the solder from the tang side and drawing it up through the joint. A thing to remember is that SOLDER FLOWS TOWARD THE HEAT SOURCE.Once cooled off wash and clean all flux from the blade.To clean up the joint make a small chisel from a piece of brass or bronze and cut the excess from the joint in smooth slices. Don't use a hardened tool like a knife blade as it will scratch the blade.Fine sand paper and buffing with a bristle wheel will remove any excess, leaving a shiny and nearly invisible joint.
There are several jigs and spring tricks that you can use to hold the guard in place, but nothing works better than a good fit that has to be tapped into place.
Hope this helps.
Stacy

 

[Stacy E. Apelt - Bladesmith]

An additional note on how to deal with gaps or pre-made guards that don't fit right. Make tight fitting shim wedges (from the same material as the guard) that fill the gaps as tightly as possible.Drive them in if necessary. Then when all is right, solder in place.This works especially well when you accidentally cut the slot too long and a little bit shows at the spine or edge end of the slot.
Stacy

 

[Rookie7]

Stacy, thanks for the concise tips. Always good to hear from the pro.