This classification, however, merely indicates the nature of the lathe with reference to the individual feature indicated in the title; thus, although a foot lathe is one run by foot, yet it may be a single or double gear (back-geared) lathe, or a hand or self-acting lathe, with lead screw and independent feed motion.
Again, a hand lathe may have a hand slide rest, and in that case it may also be a back-geared lathe, and a back-geared lathe may have a hand slide rest or a self-acting feed motion or motions.
Fig. 480.
[Fig. 480] represents a simple form of foot lathe. The office of the shears or bed is to support the headstock and tailstock or tailblock, and to hold them so that the axes of their respective spindles shall be in line in whatever position the tailstock may be placed along the bed. The duty of the headstock is to carry the live spindle, which is driven by the cone, the latter being connected by the belt to the wheel upon the crank shaft driven by the crank hook and the treadle, which are pivoted by eyes w to the rod x, the operation of the treadle motion being obvious. The work is shown to be carried between the live centre, which is fitted to the live spindle, and the dead centre fitting into the tail spindle, and as it has an arm at the end, it is shown to be driven by a pin fixed in the face plate, this being the simplest method of holding and driving work. The lathe is shown provided with a hand tool rest, and in this case the cutting tools are supported upon the top of the tool rest n, whose height may be adjusted to bring the tool edge to the required height on the work by operating the set screw s, which secures the stem of n in the bore of the rest.
To maintain the axes of the live and dead spindles in line, they are fitted to a slide or guideway on the shears, the headstock being fixed in position, while the tailstock is adjustable along the shears to suit the length of the work.
To lock the tailstock in its adjusted position along the shears, it has a bolt projecting down through the plate c, which bolt receives the hand nut d. To secure the hand rest in position at any point along the shears, it sets upon a plate a and receives a bolt whose head fits into a T-shaped groove, and which, after passing through the plate p receives the nut n, by which the rest is secured to the shears.
To adjust the end fit of the live spindle a bracket k receives an adjusting screw l, whose coned end has a seat in the end j of the live spindle, m being a check nut to secure l in its adjusted position.
The sizes of lathes are designated in three ways, as follows:— First by the swing of the lathe and the total length of the bed, the term swing meaning the largest diameter of work that the lathe is capable of revolving or swinging. The second is by the height of the centres (from the nearest corner of the bed) and the length of the shears. The height of the centres is obviously equal to half the swing of the lathe, hence, for example, a lathe of 28-inch swing is the same size as one of 14-inch centres. The third method is by the swing or height of centres and by the greatest length of work that can be held between the lathe centres, which is equal to the length of the bed less the lengths of the head and tailstock together.