Standard-length drills may flex and wander a
small amount when they first start to penetrate
the surface of the work. The flexing may cause
the starting point to be off-center and therefore
the drilled hole may be off-center and not
perfectly parallel to the axis of the workpiece.
Therefore, it recommended always to use a
center drill to start a drilled hole
Center drills are available in many sizes and
made of various materials, much like drill bits.
For work on the SC4, a set of 5 HSS center
drills, #1 through #5 in size, will meet most of
the needs the operator is likely to encounter.
Set of five Center Drills
Tailstock Chuck and Arbor
For most drilling operations, the drill bit is held
in a Jacobs-type chuck mounted in the
tailstock by means of a #2 Morse Taper arbor.
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Since the chuck and the arbor are purchased
separately, care must be taken that the front
taper of the arbor that mates with the chuck is
the proper size for the chuck.
Chucks for use on a lathe usually have a
female Jacobs Taper, so an arbor is needed
with a #2 Morse Taper on one end and a
Jacobs Taper matching the chuck taper on the
Arbor for tailstock chuck
Arbors, such as the one in the photograph,
often have a flat tang at the end of the Morse
Taper, used to drive the arbor in some types of
machinery. For use in the SC4 tailstock, the
tang needs to be cut off using a hacksaw,
metal-cutting bandsaw or abrasive cutoff wheel.
Part of the Morse Taper may also need to be
cut off in order for the arbor to fit properly in the
The chuck generally is permanently mounted
to the arbor. To do this, first wipe the JT end of
the arbor and the corresponding JT taper in the
end of the chuck with a clean shop rag to
remove any oil, grease, chips or grit. It is
important that both mating surfaces be free
from any contamination to ensure a tight,
secure fit. Insert the JT taper end loosely into
the chuck taper, then rap the opposite end of
the arbor firmly on a board to drive the tapered