LATHE OPERATIONS - OD1645 - LESSON 1/TASK 1
(b) A bored taper may be checked with a plug gage by marking the gage
with chalk or Prussian blue pigment.
Insert the gage into the taper and
turn it one complete revolution. If the marking on the gage has been rubbed
evenly, the angle of the taper is correct. The angle of the taper must be
increased when there is not enough contact at the small end of the plug
gage, and it must be decreased when there is not enough contact at the large
end of the gage.
After the correct taper has been obtained but the gage
does not enter the workpiece enough, additional cuts must be taken to
increase the diameter of the bore.
(c) An external taper may be checked with a ring gage. This is achieved
by the same method as for checking internal tapers, except that the
workpiece will be marked with chalk or Prussian blue pigment rather than the
Also, the angle of the taper must be decreased when there is not
enough contact at the small end of the ring gage and it must be increased
when there is not enough contact at the large end of the gage. If no gage
is available, the workpiece should be tested in the hole it is to fit. When
even contact has been made throughout the workpiece, but the tapered portion
does not enter the gage or hole far enough, the diameter of the piece is too
(d) The taper per inch of any external taper may be obtained by dividing
the difference in diameters by the length of the taper in inches measured
along the axis of the workpiece between these diameters.
For example, to
find the taper of a workpiece, or to check whether a taper is being turned
correctly, the following method may be used with a pencil or a scriber, draw
two lines on the surface of the taper parallel with the ends and, if
convenient, a whole number of inches apart. Measure the diameters at these
lines and divide their difference by the number of inches between them, the
result will be taper per inch. The formula to use when computing taper per
inch (tpi) is the same as the one given in paragraph 6j(2)(c), pages 67, 68
(5) Standard Tapers.
(a) There are various standard tapers in commercial use, the most common
ones being: The Morse tapers, the Brown and Sharpe tapers, the