Figure 15-3-1
| A left-hand thread is a thread that when viewed axially (from the end) winds in a counterclockwise direction (Figure 15-3-1). |
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| Left-hand threads are designated with an LH at the end of the thread designation,
such as
3/4-10 UNC LH. Left-hand threads are used in applications where the nut may loosen because
of the rotation of the motor or spindle. The procedure for cutting left-hand threads is
the same as that used for cutting right-hand threads with two notable differences: The
compound must be set at 29 degrees to the left of the operator (Figure 15-3-2), and
the leadscrew direction is reversed so that the threading pass is made from the left to
the right (Figure 15-3-3).
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| Left-hand threads typically require a recess at the thread start location. Keep in mind when grinding the left hand threading tool that the side cutting edge angle on the left-hand thread cutting tool is opposite that of the right-hand thread cutting tool (Figure 15-3-4). |
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