MILLING MACHINE OPERATIONS - OD1644 - LESSON 1/TASK 1
fixtures, have keys or tongues on the underside of their bases so that they
may be located correctly in relation to the T-slots.
b.
Methods of Mounting Workpieces.
(1)
Clamping a Workpiece To The Table. When clamping workpieces to the
worktable of the milling machine, the table and workpiece should be free
from dirt and burrs.
Workpieces having smooth machined surfaces may be
clamped directly to the table, provided the cutter does not come in contact
with the table surface during the machining operation.
When clamping
workpieces with unfinished surfaces in this way, the table face should be
protected by pieces of soft metal. Clamps should be placed squarely across
the workpiece to give a full bearing surface. These clamps are held by T-
slot bolts inserted in the T-slots of the table. Clamping bolts should be
placed as near to the workpiece as possible. When it is necessary to place
a clamp on an overhanging part of the workpiece, a support should be
provided between the overhang and the table, to prevent springing or
possible breakage.
A stop should be placed at the end of the workpiece
where it will receive the thrust of the cutter when heavy cuts are being
taken.
(2)
Clasping a Workpiece to the Angle Plate. Workpieces clamped to the
angle plate may be machined with surfaces parallel, perpendicular, or at an
angle to a given surface.
When using this method of holding a workpiece
precautions should be taken, similar to those mentioned in (1) above for
clamping the workpiece-directly to the table. Angle plates may be of either
the adjustable or the nonadjustable type and are generally held in alignment
by means of keys or tongues that fit into the table T-slots.
(3)
Clamping Workpieces in Fixtures.
Fixtures are generally used in
production work where a number of identical pieces are to be machined. The
design of the fixture is dependent upon the shape of the piece and the
operations to be performed.
Fixtures are always constructed to secure
maximum clamping surfaces and are built to use a minimum number of clamps or
bolts, in order to reduce the time required for setting up the workpiece.
Fixtures should always be provided with keys to assure positive alignment
with the table T-slots.
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