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Charles Lewton Brain

Hints on making tubing

by Charles Lewton-Brain - © Brain Press Publications - 1997
Not all sizes and wall thicknesses of tube come seamless from a factory or refiner. Especially when working in gold it is not cost effective or timely to order in a specific tube size, material, or wall thickness. There are many times when you need a piece of tubing, you don't have it, and you can't wait a day or so to order it in or run across town and buy it. In general, it is possible to make the length of tubing you require for an object in about fifteen minutes. When compared with the time required to go across town to buy the tube, or order it in, as well as paying more than the cost of the material for the privilege of buying ready-made tubing, it is clear that making your own is a cost-effective, rapid way of obtaining it. When you need very thick walls it is particularly important to be able to make your own tubing.

To make tubing you have to define your needs: what wall thickness what outside diameter what inside diameter what material type you need. Did you plan for the material and structural requirements when in use in your hinge?

Some goldsmiths keep a few sizes (generally larger ones) of gold tube in the shop and then rapidly draw it down to the sizes they need when a job comes up. This saves having to buy a large selection of sizes to have on hand.

You will also need some tools for drawing. Drawplates in larger sizes are essential. They should be steel and are rather expensive. For very occasional use a wooden draw plate, or brass, delrin or nylon may be used. Best is a proper steel one. While one can draw tubing by hand, in the larger sizes and thicker walls it is really pleasant to have a draw bench.

Because, for all intents and purposes, the wall thickness of a tube does not change during drawing, unless you're down in the very small sizes, you start out with the wall thickness on you want to end up with. Only when a tube has been drawn very small (for example, with an inside diameter of less than 0.5 mm) does the wall thickness appear to change and begin to thicken while drawing the tube.

Let us assume then that I wanted a wall thickness of one millimeter on a tube with an outside diameter of 3 mm. I would first determine the circumference of a 3 mm diameter tube. C (circumference) =P x D (diameter) so we would multiply 3.14 times 3 to obtain 9.42 mm (P=pi=3.14 more or less). This represents the minimum width of the blank required to make the tube. The sheet used would be 1 mm thick.

 

C = P x D
C = 3.14 x 3
C = 9.42 mm width of blank.

In order to have a nice round tube and get a reasonable length with a tightly drawn seam we start bigger than this so I might choose a blank width of 12 mm or more. We have to plan for some material for a tang to draw the tube with and so we will make the length of our blank at least as long as the final desired length of the tube, plus the tang length (if not longer). The end of the tube to be drawn is cut at a broad taper, and the sides of the strip that we are going to be using to make the tube are parallel.

It is pretty much the same amount of work to draw a short tube as a long tube so you might as well make it quite a bit longer than you need, so that when you draw the tube, you get more than you need, and so develop a stockpile of tubing in various sizes and wall thickness in the process of doing the work you were doing anyway. Often with tube making it is worthwhile making a much longer tube than you need, and cutting off 2 inches. (5 cm) from the back every few holes as you draw it down. In this way you end up with a great selection of tubing in graduated sizes. This is particularly worthwhile with thick-walled tubing. An important principle: always make more than you need-it is the same amount of work and you will need some more tubing at a later date.


actual tube width we will start with

Sometimes, particularly with precious metals such as gold, one doesn't feel like utilizing material for the tang, which will just end up as scrap, so one can take a small piece of brass or even silver wire, and solder it onto the end of the rectangular blank from which one makes the tube. This will serve as a tang to draw with. For gold and similar costly materials it can be a good idea to avoid some wastage by soldering on a wire of a less expensive material instead of making a taper to draw the tube with.

When all is said and done, and the tube is finished, you unsolder that small wire tang, and this way you didn't have to use up some of your gold in a tang for drawing. If I do this I will taper roll the wire and tube beginning to blend them into each other. Roll the end in slightly, back it out and put it in again at 90o to the first direction, then go to the next smallest hole and do the same thing only not as far in on the wire. Continue in this way until you have a smooth tapered point.

Tubing, too, can be step rolled to get a taper on the end for drawing it. You make the tube without any taper to the blank. Then you taper the end with the wire rolling mill as described above. This gives you a solid tang to draw with but the tang material becomes scrap at the end of drawing. One can solder the tapered end for more strength while drawing.

I like to shape my tubing blanks into wood-that is, that I will take a stump and I will use a forging peen, or the peen of my bench hammer, and make a groove or dent into the endgrain of the wood, then shape the tube into that to obtain a half round cross-section. I don't like to use commercial tube-shaping swage blocks, which are steel blocks with half round grooves in them, because I find that they tend to damage the sheet metal of the tube quite a bit during the making. So, again, for me, it's a wooden shape of some type that I form into. The blank is tapped into the groove using the hammer, and rolled sideways while tapping onto it, back and forth, so that the sides of the groove form the metal around the hammer at the same time as the hammer is pushing the tubing blank into the groove. First of all, we shape it into a "U"-shaped cross-section. It is at this point that we can "true up" the two sides of the blank they are now in the same plane and so we can file down the length of the blank, evening up both of them simultaneously.

When you hammer and shape, don't make small dents or nicks you want the shaping to be as smooth and un-bumpy as possible. After you have reached the "U"-shaped position, you then begin hammering at about forty-five degrees to the edge of the trough. You hammer gently while rolling the blank back and forth until the cross-section of the tube becomes somewhat pear-shaped, perhaps even a little bit teardrop-shaped. At this point, we can tap it so that it is more or less round, and we can begin drawing it through the drawplate.

It's perfectly possible to draw tubes under about five or six millimeters in diameter by hand, but for over this size, or for tubes with a very heavy wall thickness, such as a two millimeter wall (which is something that one does sometimes) it is preferable to use a draw bench of some type. We draw the tube through the drawplate until it is smooth and round. At this point, I stop, and I will inject a watery flux solution inside the tube until I see flux run out the bottom of the tube to make sure that the interior seam is protected, then I flux the outside of the tube, and anneal the entire thing. This releases any stresses built into it from making it, and the gap, the seam, will open slightly. Rinse it off with hot water to dissolve and remove flux residues-do not pickle it (we don't want a pickled finish inside our seam because solder does not like to flow onto pickled surfaces)-and then draw it through the last hole that it went through in the drawplate, just to tighten it up. At this point, the seam is tight-as tight as it's going to get-and you have just removed all stresses by doing the annealing procedure. Then re-flux the interior of the tube with a syringe as before, flux the outside as well and solder it, if it's going to be a soldered tube. When drawing it down further, to find the correct hole to draw it through next, take the back of the tube and try and push it into the hole you think is right. When the tube will not go in then the correct hole to use is the next one down, the next smallest hole.

After soldering, any spilled solder is cleaned up, the tubing is pickled, and then it is drawn further until you have reached the outside diameter that you require. One of the things you have to watch out for in making your own tubing is having overlaps of the seam, so when you're closing it up with the hammer, before you even begin to draw, make sure that everything is nice, clean, that the seam consists of even butt joints, and that you have no overlaps occurring.

Another thing that can sometimes occur, is that during drawing the tubing twists, so that your seam is not a straight line down the length of the tube, but in fact twists or spirals around the tube, which is not a happy situation. The way that you fix this is, while you are drawing it, you place a jackknife, held carefully, clamped securely with pliers, in front of the drawplate, and insert the jackknife into the seam of the tube at the same time as the tube is drawn. This will automatically straighten up the seam into a single, even, parallel line.

A warning: if you press down too far with the jackknife, you'll end up with two half-tubes-I've been there, done that. For much hinge-making, we don't, in fact, use soldered tubes, because, if you do, then when you install the tube into your hinge, you don't know where the seam is, and usually it's in a nice, open, wrong position, and the solder flows out of it during the solder job, and then you're left with a visible gap or a seam. So, if we're going to be using tubing for hinges, often we do not solder the seam until we're actually installing the hinge knuckle in place, and during that installation, the seam is then soldered closed at the same time as the tube knuckle is soldered down, combining both steps and ensuring that the tube seam faces inwards and so is hidden on the finished piece.

Drawing thick walled tubing
Thick-walled tubing has special applications for hinge-making, and there are some silversmiths' hinges that only work if they're constructed with very thick-walled tubing. Certain bracelet hinges, too, require that the walls be quite thick and strong in order to have the bracelet function, or the catch function, as will be seen in the discussion of hinge-based catches. There are some hints for drawing thick-walled tubing. When drawing thick-walled tubing, it helps to have a draw bench for the extra force that's required, and the sheet metal thickness that you start out with is, more or less, the wall thickness of the tube that you end up with. Definitely start with a fairly large diameter tube it is much easier to make the tube that way and you end up with a lot more tubing. Again, for the larger sizes, wood, Delrin and homemade steel (even unhardened) drawplates will work. All you need are tapered holes in the plate. As always make sure there are no overlaps at the seam.

Drawing wire inside
Sometimes a solid core is used to obtain a fixed size of hole in a drawn tube. When the inside diameter needs to be a very exact size, goldsmiths will draw a wire inside the tube at the same time as they're drawing the tubing down. Usually you draw a tube with a core in it only a little bit (through just a few holes) unless the core wire is much harder than the tube material, as softer cores can bind really effectively into a tube when drawn together. If you use a core, make sure that a good portion of it projects out the end of the tube being drawn so as to allow you to grip it and draw the core wire out again when done. A steel core wire is best as core wires of softer materials may bind and snap off when you are trying to withdraw them at the end. I like stainless steel the best for this.

It can also help to lubricate the core wire with oil or graphite (a pencil lead) prior to drawing to ease its eventual removal. A polished wire core helps as well. The way that it would be removed at the end, is by placing the back end of the tube against the drawplate with the wire that's inside fitting through a hole in the drawplate, and then drawing against the drawplate to withdraw the wire from the tube. A very good selection of hard-drawn, high-polished, stainless steel wire in a number of sizes is available from Small Parts Ltd. (see sources).

With a gold tube it is also possible to use a core wire of copper or aluminum which is then etched out at the end of the drawing procedure. This procedure is, however, time-consuming and involves dangerous acids or caustic chemicals. Nitric acid, ferric chloride or even hydrochloric acid are used for a copper core-depending upon which acid will not affect the material of the tube that you drew around it: hydrochloric acid or sodium hydroxide (lye) for an aluminum core wire. I have heard that people who have done this got so impatient with the speed of the core removal that they drilled a number of holes into the tube at different places to allow the acid access and then had to plug the holes afterwards. So in general, I don't recommend attempting to remove a wire from inside the tube with acid. I think that if you have to resort to this approach, there is probably something wrong in your design process and you should be able to avoid this situation by more careful planning. Any acid use would require proper safety equipment and chemical handling experience.

If you do use a steel wire-not stainless, but ordinary steel wire-as a core, for drawing inside, and if it by chance breaks off-and yes, I've seen this happen-then we can remove the steel from inside by simmering the tube, if it is a silver or gold tube, in a very concentrated solution of alum and water. You purchase the alum at the supermarket-it's in the pickling section-you make this concentrated solution, you simmer it, and the iron will be eaten out. This method is also used for removing drill bits when they break off inside a piece of jewelry.


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