For the simpler classes of fancy weaving, designated stavework, tappets are often used. These are arrangements of plates carrying projections to raise the healds when required, the plates being placed so that the projections in several plates which are to act at one pick are in line with each other, so as to raise the different healds at one and the same time. Tappets are fixed either above the loom (and are named motions or Jamieson’s tappets), or at the side of the loom—as, for instance, the Woodcroft tappets. In some cases, for three and four-shaft twills, under-heald tappets are used, and fixed on the twill-shaft previously referred to (page 76). In setting out a tappet—for a sateen motion, for instance—first get our pattern, [Fig. 41], which is composed of [Fig. 39], a satin, and [Fig. 40], a plain for the selvage. [Fig. 41] is the pattern on 7 healds and 10 picks to the round, that number being the least that will contain both 2 and 5 without remainder. The draft being straight over the pattern is also the lifting plan, and the first plate is required to lift the healds at the 1st and 6th picks. Dividing a circle into 10 parts, we take the first part, and allowing half a revolution of the crank-shaft for dwell, obtain an inclined portion C for the raising, and D for the depression of the heald (as described in Chapter IV.), by dividing E C into six parts, and describing six arcs of a circle, afterwards drawing a line diagonally. The tappet follows the circumference of the inner circle until it arrives at the 6th pick, when another projection must be raised. The complete tappet follows the form shown by the thick line.
FIG. 39. FIG. 40. FIG. 41.
It will be seen now that, as the tappet only moves 1/10th of a revolution for one pick of the loom, the heald connected with this plate will be actuated just as is required in the treading plan.
Four other similar plates must be cast for the other satin healds, which five will be bolted together so as to have projections at the 1, 3, 5, 2 and 4 picks, as shown at A. To these are bolted two plain plates, or, as is more usual, one casting equal to the whole seven. The plates for plain show an alternate projection and space. By the kindness of Messrs. Willan & Mills, of Blackburn, a sketch of their loom with one of these motions (Smalley’s patent) affixed to it is shown.
FIG. 42.