Ring Sizing
Ring Sizing
Ring sizing is a fairly straight-forward process, and one of the most commonly used by the bench jeweler. It involves either adding or removing a piece of metal from the shank of a ring to increase or decrease the diameter, or ring size. 2.61mm added to or removed from the shank will change the ring by one full size (US sizes). There are a variety of techniques used to affect the size of a ring.
SWAGING
There are two techniques that can be used to reduce the size of a ring: swaging; or removing a piece of the shank. Swaging requires the use of a set of dies and press to force the ring into the die. Most commercial ring stretchers have a swaging set at their base. Swaging should only be used on plain half round wedding bands that are not tapered. It is important that the band has not been cut and sized before. This will affect the ability of the metal to upset (swage) uniformly. Flat bands and bands with patterns will be distorted by this process.
Begin by annealing the band. Select a die that allows about one third of the band width to protrude above the die surface. The surface of the die should be polished and free of any defects or rust. If the press has an adjustable ram, set it so the ram does not touch the surface of the die plate when it is at the bottom of the stroke. It is not necessary to lubricate the ring or die when it is being swaged.
Center the ring in the die and position it under the ram. Slowly lower the ram and allow it to level the ring in the die. Using firm pressure, push the handle of the ram down about half of the stroke. Raise the ram and turn the ring over and repeat this process. Because this process tends to roll the edges of the ring inward, it is necessary to reduce the ring size one half size smaller than the intended size.
Now position the ring on the ring stretcher or steel ring mandrel and bring it back to the desired size. This step will eliminate the cupping that is produced on the inside of the shank from the rolled edges. After swaging, the ring should be stress relieved and polished. If the size of the ring must be reduced by more than two sizes, this technique is not recommended.
SIZING
If the ring is cut to be sized it must be rejoined. There are two common joints used butt and dovetail. The butt joint is formed when the shank is cut flat on the ends, and brought together to form a tight seam or joint. The dovetail joint is formed by making a “V” shaped cut or notch in the shank (when viewed from the side) and shaping the other side of the joint into a blunt point to match the “V” (Fig. 1). Although the butt joint is more commonly used of the two, the dove-tail is a much stronger joint. The main reason for its infrequent use is due to two factors; the jeweler is not familiar with this technique or the joint is difficult to fit properly. Because most jewelers are familiar with fitting a butt joint, I will focus on fitting the dovetail.
One of the more common problems that jewelers have in fitting the dovetail is caused by trying to make the angles too sharp (acute). The “V” should be fairly open, no sharper than 90° and open no more than 120°. This angle can be cut in one of two ways, sawed or filed. Personally, I prefer to form the joint by sawing. Lay the ring flat on the bench pin and loosen one end of the saw blade and pass it through the ring. Slowly saw halfway through the shank (from the inside outward) at a 45° angle. Be sure to keep the saw perpendicular to the shank. Loosen the blade and remove the ring from the saw. Put the ring back on the bench pin and from the outside saw inward to the previous cut at a 45° angle, opposite the first cut, to form a “V”. Use a #1 saw blade to make the cut, and the fitting will be much easier. This will form the female side of the joint.
To form the male end of the joint, I use a pair of diagonal cutters ( a heavy pair of wire cutters) to form the basic shape. The final shape can be formed very quickly with the use of a flat hand file. Use long straight strokes to keep the surfaces flat. Trial fit the joint and make any adjustment to make the surfaces set flush. If you are adding a plug to the shank (sizing up) don’t try to fit both ends at the same time. Concentrate on one end and solder it into place before fitting the other end. This will make the fitting process much easier.
When using a file to form the “V,” a square needle file is a good choice. It is important to use long smooth strokes to keep the surfaces flat. Use a saw to start the groove in the center of the shank to allow the file to track along. A #1 saw blade works well. It is not necessary to make the cut any deeper than the saw blade. A three corner file also works well, but keep in mind that the angle must be opened up, so only file one surface at a time. Care must be taken to prevent the corner from drifting into the opposite surface. After one side is fit, solder it into place (if the ring is being sized up) and begin fitting the remaining side.
The soldering process is fairly straightforward. There are a few considerations that should be noted. First, be sure to protect the surface of the metal from oxidation with a powdered boric acid and alcohol solution before heating. Flux the joint to further prevent oxidation and reduce surface tension to allow the solder to flow. Remember that solder always flows toward the heat, so heat the joint from the opposite side that the solder is placed. Always heat the mounting and never the solder directly.
If solder erosion does occur, it usually happens on the side that the solder is placed onto prior to melting. If the solder is placed on the inside surface of the ring and drawn through to the outside surface, pitting along the solder joint can usually be reduced. In addition, the solder is much easier to position and remains in place better during the heating process.
When heating the shank, it is best to heat along the shank, not back-and-forth, in line with the solder joint. Use an on/off heating technique while heating the shank. This will allow the heat to stabilize in the shank and give better control over the solder flow. Do not try to over flow the solder. Remove the heat source the moment the solder flows through the joint, even if some solder remains piled on the opposite side. Solder only needs to flow to the outer surface of the joint and not flood over the surface of the shank. Trying to flood the solder over the surface is the main factor in overheating the solder which promotes solder erosion. Solder erosion will appear as a group of small pits in the area of the solder. These pits will be along the edges of the joint and not in the joint itself.
Before the shank is rounded out again, it is best to file the inside joint flush. Leaving the joint uneven while rounding can add undue stress to the solder joint and may lead to failure. After the inside is filed flush, use a rawhide mallet or dead blow mallet to round out the shank.
Slide the ring over the mandrel and pull it tight. Strike the shank directly against the mandrel and not with a glancing blow. Remember, the goal at this time is to round out the shank and not adjust the ring size. If the ring size remains a little smaller than the required size, use a steel hammer (a chasing hammer is good) and tap the shank lightly directly against the mandrel to increase the diameter. Never try to wedge the ring down the mandrel to increase the size. This practice will often deform or torque rings with a gallery top and limit all control over where the metal is stretching. If the ring has been sized up, hammer against the plug to increase the size. The plug should be slightly thicker than the surrounding shank, and the slight thinning effect of hammering the shank will not affect the overall shank thickness.
After the ring is round and to size, file the shank to the proper shape. If the sides of the shank are filed first it is much easier to edge to contour and thickness of the shank. Be sure to remove all excess solder (if any) surrounding the joint. Use an emery buff stick to remove the file marks on all surfaces of the shank. The ring can be polished in the conventional manner.