Soldering tubing

[Lemosteam]

I am making some streetlights using brass washers and 1mm O.D. tubing. The I.D. of the tube is about 0.55mm. See the latest weekend update.

When I touch a very small amount of solder between the washer and tube O.D., solder always fills the I.D. Of the tube, forcing me to drill it out, making it difficult to push the magnet wire though the tubing.

My question is this. Is there any substance I can put into the end of the tube that will repel the solder flow, or prevent it altogether?

[GaryHinshaw]

Maybe a (very) sharp pencil tip?  The graphite won't take solder or act as a heat sink.

[woodone]

How about using a round tooth pick?

[TrainCat2]

I have used a round toothpick as well, but I soldered differently. Put the washer on the toothpick, use TIX Flux and tin the washer. Tin the end of the tube and the toothpick will help line-up the two openings. Touch the iron to the joint and your done.

[C855B]

Anti-flux. No kidding. It exists, or at least it did. Last time I used it had to have been 25 years ago. I’ll rattle around in my old electronics toolboxes to.see if I hadn’t thrown out the dried-up tube.

[Tjack757]

Try some mineral oil

[peteski]

boB's idea sounds must useful to me.  Yes, Tix (company that makes the flux and soft solder) also makes Anti-Flux.  I have it and tried it, but I didn't have much luck.  It is a orangy colored liquid.  I still have the bottle but the stuff dried out.  I suspect I coudl just add water to liquefy it again. But here toothpick is a winner to me.

[Lemosteam]

boB's idea sounds must useful to me.  Yes, Tix (company that makes the flux and soft solder) also makes Anti-Flux.  I have it and tried it, but I didn't have much luck.  It is a orangy colored liquid.  I still have the bottle but the stuff dried out.  I suspect I coudl just add water to liquefy it again. But here toothpick is a winner to me.

I’ll try the toothpick, bit I’m not sure I can whittle it down to fit in the ID of the tube.

Also thought of flaring the tube a little too, again not sure what tool I can use to do that either. I might have to grind  a nail or something down.

[TrainCat2]

Alternate method: Use K&S Metals .016 cold steel music wire for the alignment and soldering the joint. The trick is to leave the treated metal surface of the wire alone as it will not allow solder to adhere until you scratch-up the surface.

I would sill use the toothpick to prevent solder in the washer ID.

[Lemosteam]

After flaring the tubing enough to prevent the washer from falling off (the 00-90 washer has too large off a hole for the tube) the pin I put in my fixture prevented the flow and the solder joint was ok.

[peteski]

I’ll try the toothpick, bit I’m not sure I can whittle it down to fit in the ID of the tube.

Also thought of flaring the tube a little too, again not sure what tool I can use to do that either. I might have to grind  a nail or something down.

You might want to consider finding better toothpicks John.

Here is are all the different wood toothpicks I use for my hobby tasks.  One can never have enough tools (or toothpicks).   
Toothpicks are pretty inexpensive.



The one on the left is the crappy flat toothpick with dull pointy end.
Next is a square cross-section toothpick with the end sharpened to conical shape.
Then there is a round bamboo toothpick which is more slender than the others and the end is also conical. It is also much sturdier than the standard wood toothpicks.
The two on the right are the same round toothpicks with conical end that  tapers to a very thin point.
The rightmost one is inserted into a 0.042" OD brass tubing (I don't have any 1.0mm or 0.039" tubing, so that seems close enough).  As you can see a good portion of the toothpick is inside the tube.  I think those would work fine for the method boB described.

[mmagliaro]

I was going to suggest the steel wire straight off, and even without whatever coating is on it, solder doesn't stick to steel very easily so that should work great.  But did you know you can get tungsten rod that small?
https://www.amazon.com/CK-T0207GL2-Lanthanated-Tungsten-Electrode/dp/B073FV5763

I knew it came small, but not THAT small!  (.020", which might just fit inside your brass tube).  Solder will never stick to tungsten.

[Lemosteam]

I was going to suggest the steel wire straight off, and even without whatever coating is on it, solder doesn't stick to steel very easily so that should work great.  But did you know you can get tungsten rod that small?
https://www.amazon.com/CK-T0207GL2-Lanthanated-Tungsten-Electrode/dp/B073FV5763

I knew it came small, but not THAT small!  (.020", which might just fit inside your brass tube).  Solder will never stick to tungsten.

Yeah, not going into production here, lol.

I bought some of those in 1/8" for underbody kits to add weight to the MT car and align the two halves.