The driving bands of foot lathes have been made of cord or rope, of catgut; of plaited horsehair, leather or catgut; of round and of flat leather, of gutta percha and of other substances. Of all these, catgut, from its durability, comparatively slight tendency to expansion or stretching and from the convenience of its form, has obtained general and almost exclusive use.

The ordinary catgut of commerce is manufactured in lengths of about seven yards, twisted as a single strand; it has a smooth, uniform, external surface and is hard and solid to the center. Extensively used for a great variety of purposes, it is made of many sizes, ranging from .025 to about one inch and a half in diameter. The different sizes are distinguished by their diameters expressed in parts of the inch, from the largest to five-sixteenths, and below that size by the numbers of the Birm. Wire Gage, page 1013, Vol. II. Catgut for the driving bands of foot lathes varies from about one to three-eighths of an inch diameter.

The power of a catgut band in the transmission of motion, depends upon the correct proportion of its size to the work it has to perform, and the extent of its wrapping contact upon the wheel and pulley. The diameter should be just large enough to prevent the band quite reaching the bottom of the groove in which it runs; the surface contact is then increased, while additional hold is obtained by the band to some extent wedging in the groove. In the case of wood pulleys, the grooves soon wear to fit the band, which then takes a semicircular bearing, and the increased surface contact thus obtained largely compensates for the loss of the angular grip. Undue width in the grooves, necessitates a band of larger and disproportionate diameter, which excess of size causes increased labour in the continual bending of the band. On the other hand, deficiency of size has to be counteracted by increased tension, which for many reasons is highly detrimental.

The two ends should be joined with the least possible addition to the dimensions of the band, for any abrupt enlargement by the joint is objectionable, causing a concussion in its revolution, every time that it runs on to the wheel and on to the pulley. The shocks caused by an abrupt or thick joint, are felt as a series of blows, more severe upon the pulley than on the wheel; every blow imparting a slight jerk to the work, with a consequent interruption of continuity of amount of cut by the tool, plainly visible on the surface produced. With pulleys of small diameters, especially on those employed for driving revolving cutters, such an enlargement of the band seriously interferes with uniform revolution ; the jerks given to the tool leaving sensible marks and almost ridges upon the work.

The ordinary methods, of joining catgut bands are by splicing, or by hooks and eyes; occasionally they are sewn or joined by wire, spirally or as rivets. Almost any methods of joining the ends of the band, must of necessity form an enlargement of its diameter; and therefore so far as possible to avoid the inconvenience above referred to, the joint should be made to gradually taper away to the size of the band, so that it may insensibly run on to the pulley when it is scarcely felt.

Catgut being formed of only a single strand, splicing does not admit of much variety; the splice should be made in the manner shown by figs. 47 to 51. Spliced catgut which is usually of moderate dimensions, is first well stretched in length, in the following manner. One end is fixed in the vice, and the loose end is held and strained by the left hand, one or two turns having been first taken with it around a tool handle, which is held in the right. The operator walking gradually backwards, pulls on the band and at the same time causes the tool handle to traverse several times to and fro, in every foot of the length.

The measure of length around the wheel and pulley of the lathe is taken with a piece of string, and according to its diameter, the catgut is cut from about six to eighteen inches longer, to allow a sufficient margin for the splice. The splice is commenced by two holes which are made with a conical steel point or small marlinspike, transversely and through the center of the catgut; and to allow for subsequent stretching, at a distance apart that would be about one inch less than that required for the length of the finished lathe band. The two ends are then passed through these two holes fig. 47, and drawn tight as in fig. 48; the splitting of the catgut by the holes, and filling these by the ends, causing an irregular enlargement of the band. Two other holes are then pierced in the band at right angles to the first pair, and the ends are passed through them in like manner, fig. 49; the two ends being placed through from the opposite sides of the band, and then drawn tight as in fig. 50. Both the free ends are then unravelled, and about a quarter of their substance is cut away from each, the portion taken being removed by a long sloping cut, from the inner side next to the splice ; thus reduced, the ends are then neatly retwisted and passed through two other slightly smaller holes, pierced as before transversely to the last, and again pulled tight. The operation is several times repeated, every time with a further portion cut away from the ends, until these become gradually and considerably attenuated, causing the splice to taper very gradually both ways from its center; the diminished ends after being passed through the last holes are cut off level with the surface. The completed splice fig. 51, is then laid across a flat surface, generally the lathe bearers, and lightly hammered on all sides to equalize the irregularities into a more uniform taper; the hammering being also frequently resorted to during the earlier stages of the splicing. The finished band does not usually run upon corresponding grooves, but is placed on the pulley upon one or perhaps two grooves too small; but it soon stretches to the correct length. Splicing is rarely used for large bands, which are generally joined by hooks and eyes ; but it is a very convenient mode of joining the smaller bands, to some of which, from the gradual increment in the joint, it is indispensable. It has the drawback that the band cannot be so readily removed, sometimes indeed not at all, as when it passes through apertures in solid portions of the machine.