Repairing The Finger Fit® Shank

One of the most common failures for the Finger Fit shank involves the stainless steel guide wire. The shank is usually forced open beyond its limits, which results in the wire being pulled out. Though it may appear to be a big problem when it happens, repairing it is a straightforward operation.

We will begin by looking at the construction of the shank. The first thing to note is that, with the exception of a small wire on the buckle, there are no solder joints on the shank. The hinges and buckle are riveted, and the guide wire is swaged in place. The guide wire has both ends flared slightly, which acts like a small stop to either lock the wire in place, or limit the distance the shank will open.

To help with the explanation, I am going to refer to the shank and the position of the individual parts as they appear on page 86 in our Findings Book, Volume 17. In the photographs, the male half of the shank (the half with the buckle) is to the right, and the female half is to the left.

When the guide wire is installed, it mounts firmly in a small pocket in the end of the male half. A punch is used to pinch the hole closed above the flared end which locks the wire in place. If the wire is pulled free from the male side, the hole must be opened slightly to remove the internal indention which will allow the wire to set in the bottom of the recess.

Since the side wall of the shank has been thinned slightly where the previous punched indention was made, it is necessary to punch the other side to secure the wire. Use a small punch with a rounded tip to swage the wire into place. Be sure to support the other side on a steel bench block to prevent bending the shank from the side. It is best to tap the punch firmly and check the wire to see if it is tight, rather than trying to tighten it in one shot.

If the wire cannot be tightened in this manner due to subsequent thinning of the side wall, try punching both sides. Other options that can be used are to solder the wire into place with silver solder, or glue it in place with epoxy.

When the wire pulls out from the female side, the repair process is very similar. One major difference is that the hole in the end of the female side is slightly oval. This helps in fitting the flared end into the hole and allowing it to pass beyond the indention in the side. The indention in the side serves two purposes. First it works as a stop for the length of travel for the wire. Second, it serves as a retaining notch for the buckle to snap into.

One important point to note is that the side walls of the female portion are thinner than the male half, and less force is required to indent the side. If a pointed punch is used, it is extremely easy to punch a hole through the wall. It is therefore important to be sure that the punch has a rounded point. Over-indenting the side is also a potential problem. If the indention is too deep, it can bind against the wire and restrict the ability of the wire to slide in the channel.

In some cases it may be necessary to flare the end of the wire slightly before putting it back into position. This can be done by holding the wire in a pair of pliers and lightly tapping the end of the wire with a riveting hammer. Care should be taken to avoid bending or kinking the wire as this will interfere with the operation of the shank. Occasionally the buckle becomes loose and requires tightening. There are a few ways that buckle can be tightened. The first is to pinch the sides in slightly to increase the friction of the buckle against the sides of the shank. Another way to tighten the buckle is to deepen the indention in the side of it. This is easily accomplished by opening the buckle to the point where the indention is just past the shank, and lightly punching the indention with the rounded punch.

If the buckle is used excessively, the hinge wire can wear and may need to be replaced. To change the hinge wire, begin by cutting off one end of the rivet and tapping the wire out with a small flat nosed punch. If you are unable to remove the wire in this manner, file the wire smooth to the side of the shank and drill through it. Take care to keep the hole centered.

Use a piece of gold wire 0.5 mm longer than the width of the shank with the buckle in place. Flare the ends of the wire with a rivet hammer until they form a low dome. Burnish the edges of the rivet smooth to the surface of the buckle, and remove the tool marks with a rubber wheel. Be sure to support the opposite end of the wire on a steel bench block while forming the rivet. The more often the ends are switched while hammering, the more even the rivets will be. Lightly buff the ends of the rivets and the task is complete.