Tube Setting -
Introduction to Setting
Charles Lewton-Brain
Tube setting is a simple method of setting that can take as little as five minutes or less. The setting is visually clean, has a professional look to it and can be done with a minimum of tools.
With a tube setting the process is easily understood. Metal is removed from a tube to allow a faceted stone to enter and be supported by the remaining uncut wall thickness of the tube. The remaining metal of the tube wall that juts above the girdle of the faceted stone as it sits on the ledge cut into the tube is then bent and compressed in such a way as to flatten and flow inwards onto the tapering sides of the stone effectively trapping it in place. Remember the decreased circumference from the original outer diameter of the tube and the smaller circumference of its final set position; the material flows into itself to enable the reduction in circumference to occur.
As it is easiest to use tube settings for round stones a round tube is normally used. One can however use other shapes of tubing if one has the appropriate stones. The recommended sizes of round stones for tube setting have a diameter from 1mm to about 6mm. It should be noted that larger sizes can be set in tubing if necessary.
In the setting, a seat for the stone is created within the tube by removing metal from the inside of it to create a form fitting ledge for the stone to sit upon. As a result the stone must be smaller in diameter than the outside diameter of the tube but larger than the inside diameter of the tube. As a rule when one places the stone on top of the tube and looks straight down at it one can see one half of the wall thickness; the stone covers the other half.
To cut the seat a choice of tools are available. The seat opening is cut to the exact same size as the diameter of the stone. One can precut the seat by placing the tube in a chuck such as that of a flexible shaft handpiece and rotating it against a burr or even a graver. For production of tube settings the same thing is done using a lathe. The flex shaft can be set up easily with hose clamps to fix the handpiece in place and allow a burr to be held into the rotating tube to cut seats. A sawblade placed upside down in the sawframe can then be used to slice off the completed setting while it rotates against the sawblade teeth allowing one to make seats and cut off several individual settings before having to reseat the whole tube in the handpiece chuck. It is possible to precut a seat and slice off a tube setting in this way in under 6 seconds per unit. Bezels for calibrated stone sizes are often made this way with the seat being precut before soldering in place on the piece.
One can remove the metal for the stone's seat by using various tools. A standard setting burr is often used in North America. This, however, has the drawback of damaging the walls of the setting severely if it is held the least bit tilted relative to the tube. This can be difficult for even a practiced goldsmith to do and therefore using setting burs often leads to poor quality tubing settings. Setting burs like this also rapidly fill with metal or even burn if too much metal removal at once is expected of them. Most professional setters, if using them, will therefore first clear metal out using a ball or a bud burr and follow up with the setting bur so it does not have to remove much material, is not filled with metal and can be more easily controlled as to what it is doing. A setting burr should be run at relatively low speed as high speed can burn them quickly.
My preference for tube setting is to use a ball burr with a medium cut. The main advantage is that it automatically stays centered in the tube no matter what angle it is held at. This allows much faster working and quickly cuts the seat, albeit with a curved profile.
Cut the seat with the burr and insert the stone to check for fit. This checking is done repeatedly. Goldsmiths and setters check everything all the time and it is a good habit to develop as it improves control and decision making tremendously. The girdle of the stone should be about 0.5 mm below the top of the setting. One can set it a little deeper or a little shallower but as a general guide 0.5 mm is a good starting point. If one cuts the seat too deep it is easily brought to the correct depth with a few gentle strokes of a file. When the correct depth is achieved, stop.
Check that the stone is level by placing it in the setting so that a light source or white wall reflects from the table of the stone to the eye. The table shows up brightly. Then place one's thumb upside down over the setting so that the setting itself is cast into shadow. The reflecting table facet will show up brightly and can be used to judge for level relative to the setting.
At this point the method of pushing the wall over the stone to hold it in place is chosen. This could be a burnisher, stone pusher, the side of the bench pin, a bezel rocker, a setting punch or even a point burnisher. A bezel rocker is essentially a rod with a cup-shaped depression in the end into which the setting fits. A variety of sizes are needed as one ideally has a rocker which fits the stone one third of the way into the concave hemispherical cup. The cup is rocked north-south, east-west and rotated to set the stone. The procedure is very fast and is a clean setting method, especially for smaller stones. The tool may be made by drilling into the center of a steel drill rod some 5 mm and then going in with a round burr (which follows the drill shaft) to cut the concave hemisphere. It is then polished using felt end buffs or a piece of soft wood in the flexible shaft with some polishing compound.
In all cases there is pressure against the part of the tube wall above the girdle of the stone such that it is tapered inwards with sufficient pressure and speed to close it tightly against the surface of the stone. If the pressure is such that work hardening occurs without the metal moving far enough then it may be very difficult to close the tube tightly upon the stone, as it will have a tendency to 'feather' or spring back from it, leaving a visible gap between the bezel wall and the stone. If this occurs then one has to use a setting punch or extreme force to push the metal downwards, in a new direction of pressure in order to tighten it against the stone. The metal should be moved as far and as fast as possible to prevent this work hardening from occurring.