The last time we were gathered here I signed off by promising to show you how to make a perfect wire wrap solder joint, but before we do, I’m going to iron out a few wrinkles following feedback from well-meaning readers that states:

  • Washing items with water prior to soldering could be a problem in hard water areas, as a deposit might be left on the job.
  • It’s not a good idea to use emery cloth or wet-and-dry abrasive material, as any residual grit particles will cause a problem when soldering.
  • Kitchen detergent contains silicone, which could prevent solder from adhering to the metal.

 

 

Lightly solder-tack the two tinned wires together, fold a return in the binding wire...

 

Righto, let’s have a look at these concerns. I used a piece of lightly rusted food can material, cleaned it with fine emery, washed it with kitchen detergent and water, rinsed it, dried it and soldered a nice big blob of onto it – easy as falling off a dead horse. Qualified information indicated that the silicone in detergent isn’t a problem, and any that remained would burn away with the heat. The water I used came from one of my fish tanks, which I keep quite hard (lots of calcium) for the fish, and any emery grains would be flushed off during the washing process. Okay, let’s get soldering.

 

...Put the end of the wire through the return loop, then pull on the straight wire (seen on the left) and...

 

IT’S A WRAP

First, I’ll let you in on a nice little trick. Consider the total length of the wrap we’re going to make to be about 20mm. Fold the end of the wrap wire back on itself for about double the length of the wrap being made, and let it form a little ‘eye’ at the fold so it looks like a lopsided hair pin, i.e. one side many times longer than the other (in metalwork terms this is called a return). Lay the return on the soldered joint of the two wires so that the eye loop is just beyond one end of the wrap section and the other end of the return is beyond the other end. Start winding the wire around the joint, heading towards the eye end of the return, and keep it tight and neat – one wind tight against the next along the section – until you make 20mm and are close to the eye of the return. Holding the wire so it doesn’t unravel, cut the wrapping wire to allow enough length to thread it through the eye. Go back to the start of the wrap, grab the end of the return with fine pliers and pull it slowly and carefully. This will pull the eye under the far end of the wrap and, in turn, the end of the wrap wire, until the eye is completely gone. Nothing will now unravel and the job is tightly secure. Nip the two exposed ends of the wire close to the wrap and inspect the fine job you’ve done.

 

...The return has gone under the end of the wrap so you can now nip the two long ends off.

 

 

TOP RIGHT: Here the soldering is complete and cold, ready for finishing.

 

 

Clean up with fine emery or a Scotchbrite pad ready for admiring or painting.

 

 

Quite similar to the wrap method of joining wires is the tube joint which uses thin-walled, small diameter brass tubing.

 

Clean the wrap with methylated spirit, alcohol or water and detergent, then rinse and wipe it with a paper towel (no more fingers on the wrap section from here on!) It’s up to you how to secure the job, but however you do it you need to be able to hold the soldering iron under the wrap. The far end of the wires could be lightly nipped in a vice, clamped to the edge of the bench or in your ‘extra hand’ tool. The soldering iron is held and maintained under the wrap and there it stays as you apply solder to the top of the wrap; you’re now heating only the solder on the surface of the steel wire plus the copper wire wrap. Copper heats up very rapidly, so it won’t be long before the entire area becomes adequately hot, whereupon the solder will flow throughout the top section of the wrap (some will also seep through to the underside). Let the solder set and then invert the job, apply the soldering iron to that side of the wrap and add solder as necessary to fill the wrap wire. You might end up with a hanging solder blob or two, but this can be picked off with the tip of the soldering iron.

 

Any excess blobs of hot solder can be removed with solder wick or a solder sucker.

 

Whilst you’re waiting for the job to cool, wipe the tip of the soldering iron with a paper wad and inspect for untinned areas. As soon as the tip is cleanly tinned, switch the power off and let the iron cool.

 

A snug-fitting drill makes a very neat cut much easier.

 

Okay, once the job is cold, scrub any resin flux off with a fine wire brush or give the area a good clean in boiling water with a drop of detergent. Any remaining solder blobs can be carefully filed down to the surface of the wrap wire. To finish, use fine emery cloth or wet-and-dry paper to clean the entire wrap which will, I can assure you, be very strong. 

IN A TUBE

Quite similar to the wrap method of joining wires is the tube joint, which involves a similar overlap of wires but uses thin-walled, small diameter brass tubing.

 

Using a tube cutter on its own results in the end of the tube being malformed...

 

 

...But insert a drill (or suitable rod) into the tube and the end is dead square, with no reduction in bore diameter.

 

Ideally we need some acid flux here, to clean the inside of the brass tubing. If you don’t have acid flux to hand, roll up a piece of fine emery cloth or wet-and-dry, wind it into the brass tube and move it around, up and down, until the inside is clean and bright. Many modellers have a problem cutting this size of brass tube, and my advice here is to use a tubing cutter, available from model shops and hardware outlets. Yes, the rotary blade will roll the end of the tube where it’s being cut... but not if you use the patented WOO method: After measuring and marking, but before you cut, insert the blank end of a drill bit for a really snug fit inside the tube. Make the cut with the drill inside and you’ll find the end is neat with no rolled edge.

Now you know how to achieve the perfect cut, you need to select the correct size of brass tube, the internal diameter of which is dependent on the diameter of the wire being used. Rather than go into a mathematical tantrum about calculating sizes, I’ll give you a ‘damned close’ method.

 

Front on, the clean-cut edge and the shadow of the rounded edge at the rear are clearly visible.

 

The consideration is the internal diameter (i/d) of brass tubing (flattened to oval shape) that would be required to neatly fit over the two wires being joined. Brass tube and wire are generally stated in imperial units but we’ll use the nearest metric size, which is much easier. To calculate the i/d of the brass tubing required, measure the wire diameter and add 3/4 of that to itself, i.e. diameter x 1.75. As an example, say we’re using two lengths of 4mm diameter music wire to be joined within the brass tube. Okay, 4mm x 1.75 = 7mm, so 7mm i/d brass tubing is required.

 

Silicone jammed against the base will stop solder from flowing out.

 

On a length of hardwood, end grain on, slide one wire into the tube and gently tap the tube down with a plastic or brass hammer until it’s flattened to an oval that allows the wire to move fully across the inside; a couple of light taps will do the job if you angle the wire diagonally within the tube. Check that both wires fit quite neatly into the (now oval) tube, and you’re ready to make the connection.

We want to achieve a nice, clean finish (i.e. with no solder showing on the outside) so we can give the brass a high shine once the joint’s complete. Paint the outside of the brass tube with correction fluid (as used for mistakes on paper) and give the inside a clean out with a cotton bud dipped in killed spirits or soldering acid, then set it aside on a paper napkin or clean toilet paper. Clean and tin the ends of the wire, just slightly longer than the brass tube. Set the two wires together, weigh the ends down to steady them, then apply a little solder to join them together lightly (this doesn’t take a lot of heat as you’re only melting the solder to form a tinned surface). Slide the brass tube into position and elect the end into which the solder will be introduced, since you need to seal the small gaps at the other end of the tube to prevent the solder from running right through. Two short sections of silicone fuel tubing do the trick here; slit the tube open and spring a piece around each wire so that they’re snug against the end of the brass tube (a short length of sticky tape or fine wire will help to hold them in place). Go over this section and dab-seal any small gaps with correction fluid to completely seal the end of the tube. If it can be done with your particular job, a flat piece of silicone material with two tight holes punched in, slid up along the wires and held in place with a spring peg works well. Solder won’t leak from this seal, and the end of the joint will be quite neat. Flat silicone can be obtained from supermarkets in the form of baking trays, cupcake holders, egg poachers and other heatproof, flexible kitchen accessories.

 

Nice and clean – an example of suitable copper wire for wrap jobs and the like.

 

When all’s ready, hold the wire in a vice or with a clamp as far from the brass tube as possible and apply your soldering iron against the side of the tube. After a few minutes of heating, introduce a length of solder wire into the brass tube opposite the side you’re heating with the iron. The solder will soon start to melt; continue feeding it in until it comes to the top of the tube and you can see that it’s attached to the wires; it will flow very slightly upwards on the wire, in an up-curved meniscus. This is one occasion where a micro-flame gas torch can be used as you’re heating only the outside of the brass tube, and it does speed the job up considerably.

Withdraw the iron (or flame) and let the job cool right down to cold. Remove the silicone bits, clean off the correction fluid and give the brass a good clean up. Done correctly this is an extremely strong solder joint, with the added bonus of a good appearance when cleaned up neatly or painted to suit your application.

Great – job done. In the final part of this series we’ll carry out some undercarriage work and attach some wheels – permanently!