What a weekend. I've scrapped $75 worth of brass bar trying to make some very simple parts. I thought I had a handle on this but I guess not.

The part is a very simple shape. It's a 0.5" shank, going into a 0.75" ball on the end (right side of the bar). I start by using a G71 to rough the ball from zero to 90 degrees on the end of the bar.

It's a standard right-turn, inserted tool. I'm using Tool Nose Compensation (TNC) so the ball will end up being true.

The cutter radius is in the offsets page (0.032") and I'm using Tip direction 3. From all I see in the manual, I treat this machine as if I'm using an SL type lathe and that all of the tip directions are from the back of the part (backward from what we see on a Toolroom Lathe).

That end turns just fine.

Then I do a G75 with the parting tool to cut a clearance valley on the other end of the bar (closer to the chuck). After the clearance is cut, I go after the 0.5" shank and completing the ball shape.

This is a standard, LH turning tool, also with 0.032" radius. I specified Tip Direction 4 in the offsets.

The problem is that it cuts just fine through the roughing phase of G71 but when it gets to the final pass, it seems that the TNC kicks in but does it in the wrong direction (cutting waaaayyy into the part--ruining it).

I thought it was I,K values or something else but this shows up in Graphics as well. If I turn the Tip Direction to zero (in Offsets), it looks fine.

What am I doing wrong? I thought that for outside turning, RH-turn=tip direction 3 and LH-turn= tip direction 4. Am I missing something?

Help?