G76 internal thread clarification - 0i TB
Two line format
New to lathes

Got an external thread working fine, took a bit of playing but also got an internal going OK.

Want to clarify in more detail what it is the controller is doing. As I understand it:

G0 X22 Z5
G76 P001060 Q50 R.02
G76 X18.2 Z-20 R0 P900 Q500 F1.5

This will give me a 20 OD external thread retracting out to 22 on each pass

G0 X16 Z5
G76 P001060 Q50 R.02
G76 X18.2 Z-20 R0 P900 Q500 F1.5

This will give me an 18.2 OD internal thread retracting inward to 16 on each pass

By changing the initial G0 position the controller decides internal or external? At what point does the controller decide which add each cut and which way to retract the tool? I'm presuming it's whether the initial G0 X is above or below the thread range in this case 18.2 to 20, what if the initial G0 is within that range?

(BTW this is on a flatbed so the tool is forward of the axis, but I don't think that makes a difference?)


Cheers, Sean