An el-chuck consists of a cast iron or cast steel implement resembling a letter L, and having the two outer surfaces or planes, named faces, specially smoothed and made right angular to each other. A tool of this sort is shown by Fig. 647, and others near it. The name chuck is given to this instrument, because it resembles a lathe chuck in having pieces of work bolted to it. An el-chuck is required when it is necessary to plane a surface of an object to make it right angular to some other surface or plane of the same object, for which purpose the chuck is fastened to a planing-table, so that one of the chuck's faces is in contact with the table's face, the other face of the chuck being necessarily at right angles to the table. The object to be planed is next bolted to the chuck with the desired surface in contact, and the right angular position is thus obtained without trouble. El-chucks are of various sizes, to suit machines and work of several classes. A narrow one, for long slender objects, is shown fixed to the table denoted in Fig. 652. In this Figure at the right-hand end, is seen a plate and bolt in use, the plate's paw holding the chuck while the other end of the plate is supported by a packing-piece shown by P. All the larger el-chucks should be provided with straight and parallel lines marked on that face of the chuck to which the piece will be bolted, or if both faces are of similar dimensions, the lines may be on both. Each face requires two sets or lots of lines; one lot should be at right angles to the face of the machine-table when the chuck is fastened, and the other lot parallel to the table, and therefore parallel to the chuck's face in contact. Such lines are useful for a rapid adjustment of all pieces having right angular boundaries.

The el-chuck shown by Fig. 648, is provided with two gussets, one of which is shown in the Figure; these are cast solid with the two arms of metal which constitute the el-shaped portion. Such gussets are very effectual for obtaining a strong chuck which will not be liable to distortion while fixing, or planing, and is therefore suitable for accurate work; but for general work, gusset chucks are troublesome because they have but little room for the plates and bolts.