Tc 9-524 fundamentals of machine tools

MOUNTING AND INDEXING WORK
An efficient and positive method of holding workplaces to
OFFSET BORING HEAD
Boring, an operation that is too often restricted to a lathe,
can be done easily on a milling machine. The offset boring
head is an attachment that fits to the milling machine spindle
and permits most drilled holes to have a better surface finish
and greater diameter accuracy.
OFFSET BORING HEAD AND TOOLS
Figure 8-21 shows an offset boring head. Note that the
boring bar can be adjusted at a right angle to the spindle axis.
This feature makes it possible to position the boring cutter
accurately to bore holes of varying diameters.
This adjustment is more convenient than adjusting the cutter
in the boring bar holder or changing the boring bar. Another
advantage of the offset boring head is the fact that a graduated
micrometer collar allows the tool to be moved accurately a
specified amount (usually in increments of 0.001) without the
use of a dial indicator or other measuring device.
NOTE: 
On some boring heads, the reading on the tool slide
is a direct reading. On other boring heads, the tool slide
the milling machine table is important if the machine tool is to
be used to its fullest advantage. The most common methods of
holding are clamping a workpiece to the table, clamping a
workpiece to the angle plate, clamping the workpiece in
fixtures, holding a workpiece between centers, holding the
workpiece in a chuck, and holding the workpiece in a vise.
Page 4-13 of this manual shows a variety of mounting and
holding devices. Regardless of the method used in holding,
there are certain factors that should be observed in every case.
The workpiece must not be sprung in clamping, it must be
secured to prevent it from springing or moving away from the
cutter, and it must be so aligned that it may be correctly
machined T-slots, Milling machine worktables are provided
with several T-slots which are used either for clamping and
locating the workpiece itself or for