Removing Screw Plugs
By Jos. A. BEIMEL,
Member National Technicnl Board, U. H. A. of A.
AMONG the most common forms of mishaps at the bench, even among careful workmen, seems to be the breaking of screws. Screws will twist in two and screw heads will occasionally snap, due to the material of which the screws are composed. Many of the cheaper grades contain poor quality of steel, while others are burned during the hardening process.
In most cases, screw heads that snap off due to being too brittle are usually too hard to drill into the remaining plug. Screw extractors are not always suitable and chemicals that eat up steel particles are not always advisable nor convenient for use, and more practical methods of removing the remaining plug must be resorted to. Screw heads that frequently snap off are those holding the ratchet wheel to the arbor. Such screw heads are usually larger. One uses a larger screwdriver in turning it, and unless the screw is of better steel, it is most likely to snap and leave a remaining portion of the screw in the arbor. Of course, if the plug can easily be gotten hold of with the tweezers, it may be readily turned out, but if it remains some depth within the arbor, then special care must be exercised in the removal of the plug, lest you find it necessary to replace a new arbor or even make one.
To remove the broken plug, it is best to begin by testing with a steel point l-lomewhat on the order of a large strong needle, or marking tool. The point of needle should rest against some slight bump on the plug, or a slight depression or small hole in which the marker or steel point can be securely placed. Test by attempting to turn the screw plug, remembering at the same time whether it is a right or left handed screw. In a number of cases such a broken screw may easily be turned out if one is careful not to mar the ends of the threaded arbor. A few attempts will usually bring it out sufficiently to where it may be gotten hold of with tweezer.
If on the other hand the remammg screw plug seems tight, then it is better to remove the arbor from the barrel and clamp it in some form of vise. Something that will not mar the outer diameter of the arbor. When once clamped, a little more power may be applied to the broken plug, using the steel point carefully, and the broken piece may be turned out.
Other cases again, the broken stud may be quite too tight and the steel point may not move it. It is then that a well pointed graver is a most welcome tool. The graver must be of the kind that has attached a form of butting end or better termed handle which rests in the palm of the hand, and is used to push against. The graver must first be brought to a sharp point on the oil stone and frequently tested while using, to be sure that the point has not nipped off. A blunt point may mess up the entire job, moreover if not well pointed, it is apt to skid or slip and run into ones finger, which is not a pleasant experience. On the other hand, if well pointed, it will rest nicely at some spot on the broken plug and be readily turned. Gravers have many shapes and one must select the type best adapted to his own use, as well as the kind of screw plug to be turned out.
To assure safety in removing plug, it is well to bring both thumbs in contact, the one of the left hand to act as a sort of guide. See illustration. The pushing is done with the palm of the hand, in which the handle rests. If the point bears well against a slight projection and starts turning even slightly, one may feel hopeful of removing the broken screw by making several attempts, until it may be gotten hold of. Of course, there is no absolute assurance that any method will remove all sorts of broken screws. Some of them are quite tight within the arbor and may be too deep to be gotten at with either point or graver. The writer has removed many screw plugs and some of them quite deep with the arbor or other plates, and believes others may derive some benefit by attempting the same method.For methods of sharpening gravers, the reader may refer to Harold Kelly's article in December, 1937, issue of AMERICAN HOROLOGIST, page 16.
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