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Making tubing is an important skill that is necessary in goldsmithing. Whether the tubing is used to make a hollow article, hinges, or sections of bezel for setting gemstones, the ability to make different diameters and wall thicknesses of tubing will stand any metal worker in good stead. It is possible to work only with commercially made tubing in a jewellery workshop, however, making specific tubing, with specific wall thicknesses and diameters gives the workshop far greater flexibility. The one disadvantage with workshop- made tubing is that is has a solder seam, whereas factory made tubing does not. However, if the seam is made correctly, this is a very small disadvantage.
Start with a piece of strip metal rolled out a little than what you wish the wall thickness to be. The metal walls will change slightly when the tubing is finished, but not so that it is a cause for concern. The sides of the strip of metal need to be completely parallel, also taper and cut the end of one side of the strip to a point to make the first draws through the drawplate easier.Once the one side of the metal is flat, use a divider to scribe the correct width. This will then be cut parallel to the flat side. Determine the width by multiplying the wanted diameter tubing by 3.14, and then adding 1.5 times the metal thickness. Make the diameter that you want a bit larger than the final size because you will be drawing the tubing to the required diameter. Always try to make a bit more tubing than you need so as to have some stock in reserve.
Then put it in a swage block and bend it roughly round using an appropriate mandrel. ( Keep in mind mandrel cannot be tapered it has to be straight- using steel round bar off cuts works well too)
Continue to do this, using a thinner and thinner mandrel / rod until the two sides meet.
Before the tubing is soldered closed, pre-draw it through a drawplate to get the sides nicely closed. Then anneal it and draw it through the same hole again. When the metal is drawn and bent it slightly work hardens. Then, when you anneal it, the seam will pull apart slightly. One pull through the last hole tightens it nicely again in an annealed state.
Once it is perfectly closed, then it is ready for binding wire and soldering. A good practice is to use your scriber and score it down the seam gently before you solder. This scratch brightens the metal at the seam, allowing for a cleaner solder joint.
Now bind binding wire around the tube to further prevent it from opening during soldering. Always use two twisted strands of wire. It allows for more even tightening and less expansion when heat is applied.
Soldered. Now use a fine file to file any excess solder before you draw it down further. Carry on drawing it down until you have the desired diameter.