Rockwell Automation 8520 9/Series CNC Lathe User Manual

Page 613

Thread Cutting

Chapter 25

25-13

Where :

Is :

E F

This parameter may be entered by using either an E- or F-word. It represents the

thread lead along the axis with the largest programmed distance to travel to

make the thread cut. It is mandatory when cutting any threads.
If the E-word is programmed, its value (sign ignored) is equal to the number of

threads per inch or inches per thread (determined in AMP) regardless of whether

inch or metric mode is active at the time.
If the F-word is programmed, its value (sign ignored) is the thread lead in inches

per revolution or millimeters per revolution, depending on the mode in which the

control is operating.
In a G34 block, E or F indicates the initial thread lead used at the start of the

threading pass.

This optional parameter provides a relative value for the start offset angle of the

thread. Its primary use is in cutting multistart threads. For example, if a

threading pass were made with a value of zero here, and then followed by

another pass with a value of 180

, then the second cut would be started 180

from the first resulting in a two-start thread. If two more passes are then made

(one with an a parameter value of 90

and one with a value of 270

), the result

would be a four-start thread.

Program the difference in the thread lead per spindle revolution (inch/rev/rev or

mm/rev/rev). The amount of K is added to the thread lead (E or F) after each

thread is cut. K may be programmed as a positive (increasing thread lead) or a

negative (decreasing thread lead) value.

The lead changes continuously during the move. At any point during the

move, you can calculate the lead with this formula:

instantaneous lead = F + (K * number of revs since the start)

Figure 25.10

Instantaneous Lead

Revolutions

K * Revs

Lead

Distance

The actions of the G34 variable lead threading operation are identical to

the G33 threading operation with the exception of the variable thread lead.

See the G33 threading section for details and examples of single-pass

threading blocks that cut parallel, tapered, or face threads.