When cutting external threads you set the compound to 29.5 degrees, and advance into the cut with the compound. This causes the cutting to occur on one edge of the thread, and the other edge is cleaned up with the 0.5 degree difference between 29.5 and 30 degrees.

What is the preferred method of cutting internal threads? One way would be to reverse the lathe's direction of rotation and cut the far wall of the tube, leaving leave the compound at 29.5 degrees, keep the same cutting direction as you use on an external thread (from the end of the tube inwards). This would require a right hand threading tool.

A second way would be to set the compound to 60.5 degrees beyond the 90 degree point, and again advance the compound to deepen the cut.

I suppose the simplest is to use the cross slide to deepen the cut, however this cuts both side of the tread at the same time, perhaps leading to poorer threads.

What method is preferred?