4. INTERPOLATION FUNCTIONS
Tapered screws and scroll threads in addition to equal lead straight threads
can be cut by using a G32 command.
The spindle speed is read from the position coder on the spindle in real
time and converted to a cutting feedrate for feed–per minute mode, which
is used to move the tool.
Fig. 4.8 (a) Straight Thread
Fig. 4.8 (b) Tapered Screw
Fig. 4.8 (c) Scroll Thread
_: End point
F_: Lead of the long axis
(always radius programming)
Fig. 4.8 (d) Example of Thread Cutting
In general, thread cutting is repeated along the same tool path in rough
cutting through finish cutting for a screw. Since thread cutting starts when
the position coder mounted on the spindle outputs a 1–turn signal,
threading is started at a fixed point and the tool path on the workpiece is
unchanged for repeated thread cutting. Note that the spindle speed must
remain constant from rough cutting through finish cutting. If not,
incorrect thread lead will occur.