Tc 9-524 fundamentals of machine tools

Turning an Eccentric with Close Center Holes
If turning an eccentric that has the different centers placed
too close together, a different procedure should be used. Cut
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TC 9-524
the stock 3/4 inch oversized and just face both ends to clean
up the saw cuts Lay out and center-drill the normal. center
axis and turn down those diameters on the center axis with the
work mounted between centers. Remove the work and
remount into a chuck. Face both ends to the required length
and center-drill the offset centers. Remount the work between
these centers and machine the eccentric diameters to size. For
eccentric work that has a limited distance between each center,
this method is safer than trying to use a very shallow center-
drilled hole to hold the work between centers (Figure 7-102).
Turning an Eccentric Using Throw Plates
If the lathe is to be used to turn a crank with a great throw,
or a throw that is greater than normally machined on a lathe
(Figure 7- 102), special throw plates must be fabricated to hold
the ends of the work while turning. The special throw plates
will be used as support blocks to enable the offset center holes
to be machined into the throw plates and allow for eccentric
turning. eccentric turning, it is not recommended for normal
lathe operations. Special crankshaft turning and grinding
equipment is available for this type of machining.
RECESSING DRILLED AND BORED HOLES
General
reamed hole. Recesses (Figure 7-103) are usually machined to
provide room for the tool runout needed for subsequent
operations such as internal threading.
A boring bar and holder may be used as a recessing tool,
since recessing tools have the same tool angles and are similar
in shape to boring tools. A high-speed steel cutting tool bit,
ground with a square nose, makes a satisfactory tool for
cutting small chambers (Figure 7-103). The sides of the tool
bit taper in from the cutting edge so that the nose of the tool is
the widest part. The tool bit must extend from the holder a
distance slightly greater than the depth of the chamber to
prevent the holder from rubbing the bore of the work.