soldering brass pipe

This question may seem a little strange, but I have a situation
where I need to solder a 1" (threaded) bass nipple into a brass plate to
make a very high current joint. How do I get the solder to flow
down all the threads? Flux the two pieces, leave it slightly loose?
Does anybody have any experience doing this?

Clean the surfaces well - since it contains threaded areas, you might need a brush since you wouldn't reach all areas with an emery cloth. Flux, then solder. If you don't get it clean, there are no guarantees the solder will flow. If this is going to be an electrical rather than a plumbing connection, you could use an electrical solder which can be bought with a non-acidic flux. That would have lead in it (probably, but there are lead-free electrical solders, too), and may flow more easily. You still need to clean things well first.

Tin both parts of the joint before assembly. Leave some solder in the roots of the threads of both parts, but not so much that you can't assemble them. Use a brush to remove excess solder when it is molten.

Apply flux to both parts and thread them together as much as you can with a pipe wrench.

Now the crests of the threads of one part are forced into the solder in the roots of the other parts.

Apply heat with a large torch (that flat plate will take a lot of heat) to melt the solder in the joint.

Take care that you don't let the molten solder run out of the joint.

While the solder is still molten, tighten the joint again. Apply more solder to produce a nice fillet wherever there is access to the joint.

When it cools the joint will be solidly connected.

joint

Clean and flux both sides and assemble the joint. The solder will flow into the threads far enough to give good contact.

what is this for, i would be inclined to braze it

Electrical Connection

Any electrical connection MUST BE MECHANICALY TIGHT!!!! Solder does NOT repeat NOT make the connection, it merely keeps the solid connection from falling apart. What makes an electrical connection is the mechanics of the joint. In order to make a solid electrical connection is to brazeweld the pipe to the plate.
Remember lead solder is a very poor conductor of electricity.

Good Luck,

The threaded pipe makes a mechanical connection with brass-to-brass connection. The solder, if applied as I described earlier, provides additional electrical connection that is probably 4 times the cross sectional area of the pipe.

The solder will provide corrosion resistance to the joint.

I suspect that if the original poster builds such a joint it will carry more current than can be reliably applied through the pipe.

I've worked on missiles, and all sorts of military electronics, and if it wasn't for solder, none of them would work. There is no way to make a mechanical connection other than with solder for many things, and proper industry standards often do not call for twisting or wrapping a connection prior to soldering...a proper electrical solder joint has a pretinned, then bent wire that goes somewhere between 170-190 degrees around the terminal post, and a visible fillet of solder, not a glob. This allows for vibration, strength, and minimum weight (important in missiles!).

brass

Brazing brass can be an arduous process without the right materials and technique.