Need help brazing nut to butt cap

J

jawilder

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Jun 27, 2006
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I am planning to do a wrapped mycarta handle similar to this one:
http://www.youtube.com/watch?v=xuiBha4kT6o

I am having a heck of a time getting the nut to braze to the butt cap. Last night I tried several different solders and brass brazing rod but couldn't find anything that held as well as I want.

I would rather not peen or thread the cap if I can avoid it, so I am looking for a good tutorial on exactly how to braze a joint that will hold. If push comes to shove I suppose I could wire weld it on. For this particular project, it doesn't really have to be clean around the joint as it will be covered up by the micarta. But I would like to find a method that I can use for all my hidden through tang knives.

First, I tried the brass brazing rod without flux, then with flux. Both held but both came off with a few taps of a hammer. I also tried the solders. I have not yet tried the high temp silver solder. All joints were clean before brazing/soldering.

Any suggestions?
Jason
 
The most important thing is to get the parent metals up to brazing heat before melting any filler rod. I like to use 1/16 brass rod with flux coat. It melts quick and easy for small joints. The joint should be hot enough that the rod melts when touched to the metal, outside of the torch flame. You should see it flow like water and get sucked into the gap of the joint. Don't quench to cool.

A slightly fuel rich flame with a 2x feather or so is good to use.

Should hold up much better than a couple hammer taps.
 
Salem, that has answered two of my questions. First I tried 3/16 rod but that was way too big. Then last night I tried 1/8 but found that was still too big. I'll try 1/16. Also, the rods I used were the same I use for pinstock with no flux. The guy at the welding shop talked me into a can of borax/boric acid that is is blue crystals. The label says to heat the rod and dip in, but I found this is messy (I wonder if it would be any good for forge welding). I'll get some better rod.

I will also try to heat the parent material better. I'll heat until the brass flows. Is that at any particular color?

So you put a sacrificial bolt into the nut to prevent brass from filling the threads?
Jason
 
Another thing is that in the joint, the melted brass will flow toward the heat.
So, heat the joint until the rod melts when you touch it to the side where the torch isn't- don't use the flame to melt the filler rod.

Andy G.
 
Usually brass will flow at a low-mid reddish heat range. Depends on your ambient light, use the rod to check for correct heat.

As for the sacrificial bolt- if you run a bolt all the way down into the nut before brazing, it'll probably get brazed in too. Then the whole works is shot. I find that the last thread or two above the end cap usually gets brass fouled.

I've played with a few methods of holding parts in alignment. The way I liked was to use a simple fixture.

Let's say the threads are 1/4 x 20. (I like 1/4 x 28 better, a finer range of adjustment, but harder to find on short notice in allthread stock.) I like to take a long coupler type nut and saw it in half to use for the butt nut. Longer threads that way. Grind the end flat, leave the finish fairly rough. Brass likes to have a toothy surface to bond to. If the nut is plated (likely) grind the plating off, too. It'll burn off when heating and foul your joint otherwise. In fact, grind all the sides round- less clearance is needed to turn it that way, and then the plating will definitely be gone.

I used a piece of heavy steel square tube, 3-4" diameter, to make a fixture out of. I lay it on it's side, and drill and tap a hole in the center of the top wall, for 1/4 x 20. I put a thin firebrick piece inside the tube section for a floor. I thread a piece of allthread down through the tapped hole in the ceiling of the fixture toward the brick floor. Install the butt nut onto the end of the allthread, just a few turns on to avoid brazing it into the nut. You could carbon black the all thread with an acetylene flame for some added security.

The butt cap is laid on the brick surface and the all thread is screwed down toward it until the butt nut sits lightly on the surface of the cap, centered correctly. The whole purpose of the jig is to hold the nut square to the buttcap for brazing, and to be able to adjust the clearance of the joint. When you have the nut where you want it, a jam nut threaded down on top of it can help to lock it in place. Even the little misalignment created sometimes by slop in the threads can mess with you.

I use thin firebrick for the floor because it's nice to braze on, doesn't warp with heat and doesn't seem to heat sink like a bare steel floor would. You don't have to use square tube, the jig could be made out of other types of scrap steel, I had the tube on hand and it seemed easiest. The bigger the tube, the more room you have to play the torch and rod around.

You don't have to tap the hole in the fixture necessarily. You could just use a clearance hole with nuts and washers. I think the tapped way to be more precise and easy to use. When you have the parts set up, before brazing, maybe take a small square just to be sure the joint is 90 degrees both ways. It may not matter so much with a wrapped handle, but with most hidden tang knives, installation and disassembly require squareness. If you tapped the hole in your drill press or a hand tapper it should be square.

As mentioned, it helps to have some tooth (60 grit scratches) on the faces of your joint. Bring the parts into contact, they can be touching fairly hard if there is tooth there. Otherwise, mated surfaces with a higher polish that are pressed together too tightly for brazing may not allow sufficient capillary action to occur. It needs to have a little room to flow into.

Braze away. And, if you can't get small fluxed rods a pinch of borax melted onto your surfaces works for flux. Heat the surfaces, and drop the flux on, that way it won't get blown off by the torch before it melts.
 
Thanks for taking the time to post that, Salem. I really like the jig idea. I really like to do hidden tang knives so a jig like that will be worth having in the shop.
Jason
 
Couple suggestions
first, why not try jewelry grade silver solder? it flows at between 1100 and 1200f, it has an extremely strong bond and it is easily worked, second, why do you not want to thread your butcap? seems like you are going through a lot of heartache to avoid a 2 minute process requiring $5.00 in tooling

-Page
 
I like the buttcap to be fairly thin and don't like to see the tang. Don't get me wrong, I've done it on several knives, but would rather not have a pommel nut or visible tang if I can don't have to.
Jason
 
This happens to be brass but will work with most metals, hi temp silver brazing alloy.
The crumb of silver solder you see in the first pic is all you need.
Ken.

102_0725.jpg
IMG]http://i253.photobucket.com/albums/hh42/kccustom/102_0725.jpg[/IMG]
 
I'm with Sunshadow. Brownell's Silvaloy flows at 1175° to 1200°. It is very easy to work with, flows well into hairline fits, and is very strong.
 
Salem, I tried your method last night but without the flux rod (I haven't had a chance to go to town to get some yet). I used 1/16 rod. It worked rather well - much better than before. I do admit that I used much much more than Ken suggested. I wasn't able to tap it off with a hammer but it did come off when I tightened a bolt in it with a 1/4" socket. I suppose they'll all come off when you do that.

What size brazing tip do ya'll use? I looked last night and saw that I am using a 5 that came witht the torch. I'm fairly certain that I need a smaller one. Which size should I get?
Thanks,
Jason
 
Are you using oxy/ace? If you're using a #5 Victor equivalent, that's a MONSTER tip for this job. GTH11 is right with his #0 tip, I use a #1 for this type of stuff and dial it down until it's about to pop out. I just don't have a #0, I'd use it if I did.

Good to hear your results are improving. Still, it should be bolt-threading-into-proof in strength. Unless you REALLY cranked that bolt in there.
 
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