This is represented in Fig. 284, in its latest improved form. It
consists of a shank, A, which fits the tool receptacle, and is bored
throughout its length for the reception of a central steel spindle,
to which is securely attached at one end the worm wheel, G, acting
as a dividing plate, and at the other the crank-formed frame, B, C,
with its small poppets, D, D. These are sawn lengthwise, and thus
spring upon the centre screws, which pass through them and carry the
revolving cutter spindle, K, L, M, in the centre of which is a slot to
receive the tool, the latter being clamped by the tightening screw,
L. There are certain points to be attended to in the construction of
this instrument, which must on no account be neglected. In the first
place, the screws which pass through the poppets must lie in the line
which would bisect at right angles that of the main spindle in the
same plane. A line, in fact (as dotted), passing from screw to screw
will pass across the centre of the end of the spindle. In the next
place, when the tool-holder, with its pulleys, is in place between D, D,
this line must be even with the _top line_ of the central mortise,
H, for the _point_ of the tool is level with its upper surface, it
being bevelled below; and it is essential that this point be capable
of being so placed as to form a continuation of the centre of the main
spindle. At E, E, are shown two of four thin pulleys. The two front
ones are removed to show the poppets. They should not be made thicker
than necessary, in order to avoid their interfering with the action of
the tool. Either pair will be used with either pulley, K, K, according
as the right or left side of the instrument is the highest, for, as
will be explained, the cutter frame is used at all angles between
the horizontal and the vertical lines, the cuts being consequently
inclined in either direction, left, or right, at pleasure. The centre
screws and points of the tool spindle must be carefully hardened.
Before commencing to use this cutter, it is necessary to test the
centrality of the point of the tool. Place the latter in its holder.
Let the part C of the instrument be turned till vertical; cause the
tool to revolve and to cut a light line or scratch on the face of the
work. By means of the tangent screw cause C to become vertical in
the opposite direction, so as to bring the other pulley upwards, and
with the small screws in the poppets set the revolving tool holder,
till the tool falls exactly on the line first made. It is, of course,
understood that the line in question passed through the _centre_ of
the work. If in both positions of the tool the central point is passed
through, the cutter tool is correctly placed. The poppet screws are
for this purpose specially, though sometimes used to place the cutter
purposely above or below the centre of the work. Compared with the
old form previously given, this pattern of universal cutter is very
superior.
[Illustration: FIG. 284.]