SCREW-CUTTING. Those who are possessed of a lathe with a slide-rest to it, which is now in very frequent use, may the screw of that rest into a pat ter,. screw, whereby to cut original right and left threaded screws of various rakes and diameters, in the following simple manner ;—The screw of the slide-rest has generally a square formed at one end of it, to fit a winch or handle upon, in order to turn the screw and urge the turning tool forward. Now it will be necessary to have another square, also formed at the opposite end of the screw, upon which a square socket can be secured by a bind ing-screw ; this socket is united with one of the forks of Hook's universal joint, formed of two such forks, with screws passing through the ends of the forks, having conical points to them, which enter into four holes made around an iron ball or sphere, at equal distances apart ; the two forks being thus affixed to the ball, at right angles to each other, and as usual in forming this kind of uni versal joint. The stem of this second fork is elongated, and has a neck or pivot made near its other end, which works in a cleft pivot-hole, formed in a standard, which is affixed on the top of a cylindrical stem, which can be fitted into the socket of the ordinary lathe-rest, and bound by its screw as usual. Upon the exterior end of the stem, beyond the neck or pivot, toothed wheels or pinions, as the case may require, must be fitted, and bound tight by a screw and nut ; and in to or upon the nose of the lathe-mandrel, a chuck must be screwed, which can, likewise, have other toothed wheels or pinions affixed upon it, next or adjoining to the mandrel, to work into the first mentioned toothed wheels or pinions. The front end of the chuck must also have a square hole made in it, to receive into it the squared end of the steel cylin der, which is to have the screw cut upon it ; and the other end of which cylinder is to be supported by the back centre of the lathe as usual.
A properly-shaped turning-tool is than to be placed and screwed fast in the socket of the slide of the slide-rest, and be brought to act upon the steel cylinder, which is to be cut into the screw in the usual manner of turning ; and, by the disparity in the proportions of the tooth ed wheel-work, the turning tool will be carried along faster or slower, so either as to cut coarser or finer threaded screws than the original one, or a similar one, thongh of a different diameter, if the toothed wheels be equal. The universal
joint here is necessary, to accommodate the change of motion from a right line to any angle less than a right angle. Should left hand threaded screws be required, an intermediate wheel or _pinion, to reverse the motion, must be affixed to the stand ard, and be brought to act in the other wheels or pinions.
The following is a simple and econo mical method of cutting original screws : You must leave the piece of steel from which you intend to form your tap a lit tle longer than necessary, and having turned it true throughout, at one end turn down, somewhat lower than the rest, a neck or space about half an inch in length ; round this space coil a piece of wire, and you will, at once, be in posses sion of a primary artificial guide, which will regulate the pitch of your intended screw. You have nothing now to do but to make your tracing-tool to the spiral groove formed by the wire, and be gin tracing your thread. By this simple method you may obtain, by varying the thickness of your wire, a screw of any re quired pitch, either right hand or left. SEALING-WAX. The wax used for sealing letters, legal instruments, &c. The best red sealing-wax is made by melting in a very gentle heat 48 parts of shell-lac with 19 of Venice turpentine and 1 of Peruvian balsam ; 32 parts of the finest cinnabar, thoroughly levigated, are then stirred in, and the whole well mixed. When it has cooled down, it is either rolled into sticks, or shaped in brass moulds. The best black sealing wax is a mixture of 60 parts of shell-lac and 80 of ivory black ; it may be perfum ed with a little Peru balsam or styrax. The earliest application of sealing-wax to its present use seems to have been made about the year 1553. The first printed account of it is said by Berzelius to have appeared in 1563. The great seals ap plied in tin boxes to certain legal docu ments are made of a mixture of 15 parts of Venice turpentine, 5 of olive oil and 8 of wax melted together, and colored with red lead.