Fig. 759.
In very small lathes the driver is sometimes driven by the device shown in [Fig. 759], which consists of a small chuck, screwed on the live spindle, and containing the live centre and a driving arm b, which passes through the chuck, and is set to any required distance out, by the set-screw c. The objection to this is, first, that either the live centre must be very short, or the arm b must be very long; and, second, if the chuck wears out of true, it carries the live centre also out of true; hence this class of driver is but little used, even in foot lathes.
Fig. 760.
In small drivers of this kind it is sometimes the practice to cut away rather more than one quarter of the thread on each side of the live spindle as shown in [Fig. 760] at a, and to then cut away one quarter of the thread on each side of the bore of the driver as at b in the figure. This enables the driver to be passed upon the spindle and screwed home with one quarter of a turn, thus saving time in putting on and taking off the driver.
Fig. 761.
[Fig. 761] illustrates a work driver very convenient for turning bolts. It consists of a piece of iron or plate p bolted to the lathe face plate f, and having jaws so as to fit to the sides of the bolt b and drive it. This not only saves the time that would otherwise be required to put on a driver or carrier but leaves the underneath face of the bolt clear to be faced up by the turning tool, an example of its use being shown in connection with the knife tool or facing tool.