Tc 9-524 fundamentals of machine tools

7-42

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TC 9-524
Duplicating a Tapered Piece
When the taper on a piece of work is to be duplicated and
the original piece is available, it may be placed between
centers on the lathe and checked with a dial indicator
mounted in the tool post.. When the setting is correct, the
dial indicator reading will remain constant when moved
along the length of taper.
This same method can be used on workplaces without
centers provided one end of the workpiece can be mounted
and held securely on center in the headstock of the lathe. For
example, a lathe center could be mounted in the lathe
spindle by use of the spindle sleeve, or a partially tapered
workpiece could be held by the nontapered portion mounted
in a collet or a chuck. Using either of these two methods of
holding the work, the operator could use only the compound
rest or the taper attachment for determining and machining
the tapers.
Standard Tapers
There are various standard tapers in commercial use, the
most common ones being the Morse tapers, the Brown and
Sharpe tapers, the American Standard Machine tapers, the
Jarno tapers, and the Standard taper pins.
Morse tapers are used on a variety of tool shanks, and
exclusively on the shanks of twist drills. The taper for
different numbers of Morse tapers is slightly different, but is
approximately 5/8 inch per foot in most cases. Dimensions for
Morse tapers are given in Table 7-4 in Appendix A.
Brown and Sharpe tapers are used for taper shanks on tools
such as end mills and reamers. The taper is approximately ½
inch per foot for all sizes except for taper No 10, where the
taper is 0.5161 inch per foot.
The American Standard machine tapers are composed of a
self-holding series and a steep taper series. The self-holding
taper series consists of 22 sizes which are given in Table 7-5 in
Appendix A. The name “self-holding” has been applied where
the angle of the taper is only 2° or 3° and the shank of the tool
is so firmly seated in its socket that there is considerable
frictional resistance to any force tending to. turn or rotate the
tool in the holder. The self-holding tapers are composed of
selected tapers from the Morse, the Brown and Sharpe, and the
¾-inch-per foot machine taper series. The smaller sizes of self-
holding tapered shanks are provided with a tang to drive the
cutting tool. Larger sizes employ a tang drive with the shank
held by a key, or a key drive with the shank held with a draw
bolt. The steep machine tapers consist of a preferred series and
an intermediate series as given in Table 7-6 in Appendix A.
A steep taper is defined as a taper having an angle large
enough to ensure the easy or self-releasing feature. Steep
tapers have a 3 ½-inch taper per foot and are used mainly
for aligning milling machine arbors and spindles, and on
some lathe spindles and their accessories.
The Jarno taper is based on such simple formulas that
practically no calculations are required when the number of
taper is known. The taper per foot of all Jarno tapers is 0.600
inch per foot. The diameter at the large end is as many
eighths, the diameter at the small end is as many tenths, and
the length as many half-inches as indicated by the number of
the taper. For example: A No 7 Jarno taper is 7/8 inch in
diameter at the large end; 7/10 or 0.7 inch in diameter at the
small end; and 7/2, or 3 1/2 inches long. Therefore, formulas
for these dimensions would read: