The operations here detailed are those by which comparative large nuts and bolts that may be three, four, or six inches in diameter, are bored, turned, and screwed. Small bolts and nuts are screwed with dies and screw-taps; but it will be seen that these processes are those that involve the use of lathes and their accessory apparatus.

Fixing Of Nuts

In some cases large nuts are forged without holes, to avoid the operation of punching them on the anvil. It is therefore necessary to treat all such with a preliminary boring on a drilling-machine, so that only a proper amount of metal may remain for the lathe process.

Nearly all the nuts now made are hexagonal, consequently the modes of fixing here given are adapted to such ordinary nuts. Those intended to be afterwards turned on proper nut-arbors need not have any portion turned while undergoing the first treatment on the chuck, only the boring and screw-cutting being then executed; the fixing for this purpose can therefore be done without poppets, by placing holding-plates to bear upon the nuts' faces. But there are several sorts of large nuts which require to be entirely turned to the specified dimensions while attached to the chuck; consequently, in order to properly set up a nut the operator must know, previous to commencing, whether the articles can be afterwards turned on an arbor, on its bolt, rod, or other piece to which it belongs, or whether it must be completely turned on the chuck.

There are two principal methods by which nuts are fixed for screwing, one of which consists in holding them in cup-chucks, and the other in holding them between poppets fastened in a disc-chuck. Those that are not too large should be held in a cup-chuck, which allows one face of a nut to be outwards while firmly fixed, and therefore allows the face to be turned in addition to the hole being screwed. This mode is convenient for a comparative small nut only a few inches in diameter or length, because, while in the chuck, the operator can easily see whether the six planes rotate truly, or whether the hole rotates truly, the nut being adjusted with regard to either the one or the other, according to whether most metal is to be removed from the inside or outside.

A large nut which requires its entire turning to be done while on the chuck must be held with poppets. At least four of these are needed, and if they are too small for the comparative large nut, six or eight are employed; but a small number of long and strong poppets are in all cases preferable to a large number of small ones, because small or slender ones bend during the tightening of the screws, and greatly tend to shift the nut or other object being fixed, out of the proper position.

During the adjusting of a nut to its exact position on the chuck, a few slightly taper steel wedges are employed, in conjunction with packing-blocks of suitable thickness. These are driven in between the chuck and that face of the nut next to it, but not till after the poppet-screws are partly tightened and the nut partly fixed. By this wedging process the nut can be placed so that its six-sided part is square to the chuck, which condition is known by applying an el-square; or if it is requisite to place the front or outer face of the nut parallel with the chuck, the wedging is continued until the outer face is seen to rotate truly by applying a dummy, which is fastened in the slide-rest. It will be found that this mode of wedging or packing is necessary for any large nut which is forged or cast with irregular surfaces, because neither one of the nut's faces can be put into contact with a parallel ring on the chuck, unless the face selected happens to be square to the six planes. One of the planes of a nut is denoted by P, in Fig. 1048.

When six poppets are used to hold one nut, each of the screw-points can be caused to bite one of the six planes ; and if the poppets are of proper length from the chuck, the screws will bite near the front or outer face, and the nut will be firmly held without any other fastening. While in this condition the outer face can therefore be entirely turned, because no plate is situate thereon. If the chuck is large enough, the poppets should be situate far enough apart to grip the six corners of the nut, instead of the six sides. It will be found that a large nut can be thus more securely held, and that the six sides can be more easily put square to the chuck, than if the screw-points were caused to bite the flat sides. This security is obtained by using packing-blocks having vee-notches. A pair of such blocks are shown by Fig. 1050, and are made of steel or iron. Each one has a flat side or surface to receive the poppet-screw point, and has at the opposite side a vee-notch or gap. A pair of these implements will consequently grip two opposite corners of a hexagonal nut, or other article of similar form. Supposing that six poppets are to be used, six of the blocks are put into position, one at each corner of the nut, and in contact with the contiguous poppet-screw. In Fig. 1049 two poppets and two vee-blocks are seen in use, gripping a nut, which is the appearance presented at the beginning of a fixing process, previous to attaching other poppets. When all the poppets and vee-blocks are applied, the tightening of the screw-points upon the blocks will cause the nut to be gradually shifted in any desired direction across the chuck, to accurately adjust it; but it will not be moved either towards the chuck or away from it, because the surfaces of the vee-gaps in the blocks are parallel with the opposite flat sides.

It may here be noticed that the stability of the nut greatly depends on the amount of gripping surface in the vee-gaps, because if no vee-blocks are employed, only the small points of the screws can grip the nut, and because of such a small surface being in contact, the nut is caused to move in various directions during tightening, and frequently very much away from the position desired.

For the fixing of a large number of nuts which may not be of great size, or not more than eight or ten pounds' weight each, four poppets are sufficient, instead of six. In this case the fixing can be effected with only two vee-blocks, one opposite the other, and in contact with two opposite corners of the nut, as indicated in Fig. 1049. The other two poppets are caused to bite two of the flat sides, consequently the poppets are at right-angles to each other. But four vee-blocks should be used, if available, and so placed that two of them are in contact with two planes of the nut, the flat sides of the blocks being next the screw-points, and the vee-gaps next the nut.