Welding a broken tang on a finished knife

S

salix_caprea

Joined
Dec 25, 2019
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5
Dear blacksmiths,

I recently finished a knife blade on a beginner's course. Later, when fitting a handle on, I wasn't totally happy and wanted to try a different handle shape.

I was a bit rough when removing the original handle which caused part of the tang to snap. The blade is supposed to have a full hidden tang.

My question is, would it be possible to weld in a piece of steel at the end were the tang snapped? Can this cause any issues in regards to the heat treatment, strength etc.?

This is the first time I'm facing this problem, so any advice is truly appreciated. I've been reading about glues as well, so I'm open to a good any option.

Looking forward to hearing from all of you!
XTchhOJ


XTchhOJ.jpg
 
sabre cat said:
Why don’t you do some file work at the back of the blade?

Effectively you will extend the tang and have a slightly shorter blade. No welding needed.
Click to expand...

Some filing has been done indeed, this picture was taken right after the incident so there's some epoxy residue left.

I forgot to specify that I would like to keep the length of the blade. This is quite a short blade already, about 8 cm. Hence, I would like to extend the tang. Any recommended option(s)?
 
Silver brazing would be better than a weld. Cut a small notch in the tang and fit your new peice into that notch well. Silver brazing will not jack up the HT. You will want to keep blade cool also.
 
Problem with welding is that if the carbon content of the steel you used to make the knife is high (which they usually are), you will face cracking issues. You could try to anneal the area to be welded, bevel the edge to be welded, hit it with a torch to raise the general temp of the area, weld while hot with stainless rod and then bury in ashes, vermiculite or any other material that will insure slooooow cooling. I suggest stainless because it is more ductile than, say, 7018.

Mikel
 
Angus McGunnigle said:
Silver brazing would be better than a weld. Cut a small notch in the tang and fit your new peice into that notch well. Silver brazing will not jack up the HT. You will want to keep blade cool also.
Click to expand...

That sounds interesting. Would you say silver brazing is strong enough, or at least as strong as welding?

You mention silver brazing not to affect the heat treatment too much. Is is because silver brazing seem a much faster option than a weld?

All the best,
Juan
 
You will have to anneal the blade and tang to weld on it, then re-heat treat

Yes. Welding will destroy the heat treat.
I don't think a heat sink would work.

An alternative to welding:
Take a piece of steel to extend the tang the amount desired
Make two thin ears longer than the tang extension, and solder on the tang extension, making a "sandwich" (ear/tang/ear)
Fit this to the knife tang, and drill for pins/rivets/Chicago screws/cutlery rivets or what ever mechanical means (not glue) you are going to use to attach the handle, through both the ears and the remaining tang of the knife.
Fit the handle and attach using the rivets/pins or whatever.

I'm not sure if this alternate would be more or less work than annealing and re-tempering the blade.
 
You could just run with it. Glue it in, abuse it as you feel necessary, and learn a thing or two about how much tang you really need.

Or, you could use this as an opportunity to learn how to make a 3 piece handle using some sort of metal for the frame in the middle.

Here's a crazy idea, use a file to taper one side (left or right side) down and do the same to your tang extension to effectively make a scarf joint. Then run two small pins through it and the handle to lock everything together, maybe after epoxying or brazing it together.

Or maybe make that scarf joint and rivet the joint together then proceed as normal with your hidden tang.
 
salix_caprea said:
You mention silver brazing not to affect the heat treatment too much. Is is because silver brazing seem a much faster option than a weld?
Click to expand...

When you weld something, you dilute the base metal, so you need to get above the melting point of the base metal. However when brazing, you only need to heat up the material to the melting point of the brazing material... not the base metal. And silver brazing (or any kind of brazing for that matter) melting point is lower than steel.
 
Kind of makes me wonder why it broke in the first place. I’d anneal it weld it then harden it again.
 
Last edited:
First, Welcome! You did a nice job on keeping your grind lines even. I like the blade shape too.

In my experience it is never worth trying to salvage projects that go wrong. :) I would either handle it the way it is or start over. Also in the knives I have re handled I have never had a tang break leading me to wonder if the knife has an existing heat treat issue as well. ( maybe not and it was just removed rough):) I would use it as a learning experience and start over. If you deiced you want to try and extend the tang you could try and bolt something in place like what was suggested above. I dont think a weld would be big enough to hold up. Sorry it broke on you. :( Good luck!
 
salix_caprea said:
That sounds interesting. Would you say silver brazing is strong enough, or at least as strong as welding?

You mention silver brazing not to affect the heat treatment too much. Is is because silver brazing seem a much faster option than a weld?

All the best,
Juan
Click to expand...

brazing would be kind of like glueing it. I would still set it up so the blade would be in water to protect it.
I am not explaining it well, but Mikel_24 does !
 
You could cut a notch, attach a bolt and do a thorough tang with a pommel. Overkill for a small knife like this.

I like the suggestion of brazing on a new tang or welding and re heat treating better.
 
You can simply clamp the blade in a heavy vise (use smooth jaws!) and weld or braze to your heart's content. Clamp it where the tang starts.
The vise will be a heat sink.
And silver brazing certainly gets hot enough to mess with the temper.
 
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