Fig. 38.—U- or Hair-pin Clamp
In most cases the clamps are vee'd in the grip (fig. 36), to ensure a better
hold and to shorten the length of the upstanding bolts.
In fig. 37 a vee block is made specially to hold two shafts, to be key-
grooved. The outer clamp plates are made to grip the shafts by the
tightening of their grub-screws. A useful provision is included, that of
the insertion of coiled springs surrounding the bolts, which throw the clamps
clear when the grip is slackened.
Clamping Plates and Packing.—
In general these are distinct and sepa-
rate, the packing being of wood or metal,
cut or selected to suit the height of the
clamp plates, the latter being kept strictly
horizontal. But as work becomes more
repetitive the packing is included with
the plate to avoid the loss of time involved in handling loose pieces.
Clamps have the form of plates, with slotted holes for bolts, or they are
of U shape (fig. 38), which affords a larger range of longitudinal adjust-
ment. They are single, or double, the latter to grip adjacent pieces, in
which case packing is not required (fig. 37). In this figure the grub-
screws fulfil the function of packing. Small screw jacks often serve as
adjustable packing. Another group comprises stepped blocks (fig. 39)
to give a range of heights.
Intermediate Attach -
ments.—Many articles have to
be fastened to an angle plate
instead of directly on the table.
This occurs when a piece must
have faces machined at right
angles, and when the shape is
such that it cannot be held on
the table without involving awkward packing-up. Faces that occur at other
than right angles are dealt with on tilting or swivelling angle plates.
Articles of another kind have to be held on machine centres, carried on
a machine table. These are used when machining has to be done in angular
relations, such as the machined splined grooves in shafts, and in the
drilling of holes from various angles. The work is carried on the centres
directly, or on an arbor, and the angular positions are set with pins in
holes, or latches in recesses, or by means of a circle divided into degrees.
The machine vice is admirably suited for holding small articles. It is used
chiefly on the shaper, the milling, and drilling machines, and occurs in
many forms, to hold parallel or bevelled pieces, to be machined in parallel or
£« 39-—Stepped Packing