Tc 9-524 fundamentals of machine tools

TPI = D - d
angle = TAN (TPI)
L
2
Where TPI = taper per inch
D = large diameter,
d = small diameter,
L = length of taper
angle = compound rest setting
The problem is actually worked out by substituting
numerical values for the letter variables:
TPI = 1.000 - 0.375
0.750
TPI = 0.625
0.750
TPI= 0.833
Apply the formula to find the angle by substituting the
numerical values for the letter variables:
angle = TAN (0.833)
2
angle = TAN 0.41650
Using the trig charts in TC 9-515 or any other source of trig
charts, the TAN of 0.41650 is found to be 22º37'. This angle
is referred to as 22 degrees and 37 minutes.
7-35

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TC 9-524
To machine the taper shown in Figure 7-62, the compound
rest will be set at 22
0
37 '. Since the base of the compound rest
is not calibrated in minutes, the operator will set the base to
an approximate degree reading, make trial cuts, take
measurements, and readjust as necessary to obtain the
desired angle of taper. The included angle of the workpiece
is double that of the tangent of angle (compound rest
setting). In this case, the double of 22°37’ would equal the
included angle of 45°14’.
To machine a taper by this method, the tool bit is set on
center with the workpiece axis. Turn the compound rest feed
handle in a counterclockwise direction to move the compound
rest near its rear limit of travel to assure sufficient traverse to
complete the taper. Bring the tool bit into position with the
workpiece by traversing and cross-feeding the carriage. Lock
the carriage to the lathe bed when the tool bit is in position.
Cut from right to left, adjusting the depth of cut by moving the
cross feed handle and reading the calibrated collar located on
the cross feed handle. feed the tool bit by hand-turning the
compound rest feed handle in a clockwise direction.