Flowline and Surface Finish Contour both support undercutting. Can you share a file?

I'd suggest the opposite > try adding all three values (XY & Z) on the G43.4 line. As an alternative, I would suggest having the Post modified to include a G43 Hxx Zxx line, inside the G68.2 call, to pre-position the Tool Tip, to the same position as where the start of the G43.4 toolpath move is. If you do this, be sure #5006.6 is set to prevent "motion on G49", and also that "G49 comes just before "G69", then you can invoke TCP. G54 G17 G90 G00 B-90. C-180. G68.2 X0. Y0. Z0. I90. J90. K0. G53.1 X-1.8735 Y3. S1000 M03 G43 H10 Z6.7 G49 G69 G05 P10000 G43.4 H10 X6.7 Y-1.8735 Z3. Z-.99445 X6.1 G01 X5.7 F25.

For Work Offsets in general, my preference is to "assign them to my Plane". (Don't use "automatic numbering" > -1 setting!) By making some edits to the Post, it is certainly easy to ensure the Work Offset is posted, and having it posted out for before the Tool Change, and also at the Null Tool Change, is certainly easy to do. Sounds like you may have solved some of this already. If you look in my signature, I've got videos of a Post Processor class I taught up on my YouTube channel. See "MP 101". 28 videos all about Post Processor Development.

Yes, it was also correct almost 5 years ago, when this thread was started.

The other thing to be aware of, is the Entity Attributes Manager. This can be used to "assign" certain geometry and/or geometry properties, to various levels. (Example: force all Solids to "Level 40"). You may already be aware > but you can go into the "Unblank" view, and "unblank" something which has been blanked. I personally, avoid using Blank/Unblank, however I use Hide/Unhide extensively. (Say you have a bunch of stuff visible on the screen. You can select "the stuff you want to see and work with", and then press "ALT + E" on the keyboard. It will temporarily "hide" all the other geometry. You can now work with just the stuff you had visible, (measure, or construct new geometry, whatever), and then press "ALT + E" when you are done and wish to bring everything back visible. This is great because you can temporarily hide stuff, then make it visible, without messing with your Level visibility.

Did you watch both the MP 101 and MP 301 (5-Axis) Post Class? Technically, there are two courses up. I uploaded part of my 4X Lathe Post Class. I really should go and find the old Lathe videos and upload them as well. Glad to hear you learned enough to do your own Post edits!

CBN Tools would also be good, but are best for finishing. They are prone to chipping. I've seen good production processes with CBN, where two tools are used, and the finisher gets swapped out to become the roughing tool, once it is worn. https://us.ns-tool.com/en/products/product_information/cbn/

Nothing says "easy to machine" quite like putting a tool to Silicon Carbide. Try 6 C. https://6c-tools.ch/en/produkte/

Better late than never! Glad to hear my response was helpful.

The purpose is multi-faceted. You are calculating the output angles, but you are not taking advantage of the architecture of the Post. The purpose is to give control over the Post and Code Output to the programmer. One of the things you may not yet know > the Post uses Miscellaneous Integers and Real Numbers > for every Mastercam Operation. This allows us as Programmers to pass data to the Post, to control the output. For example, on a Tilt-Trunnion Post, sometimes the calculations make the part "rotate away" from the Operator. The code will work, but you can't easily see and watch. Wouldn't it be nice if you could use a switch to control the Tilt Axis? Well, you can. The Generic Fanuc 5X Mill Post uses Misc. Integer #10 to control this tilt. (1 or 2 flips between Positive and Negative) The Post, in the encrypted section, keeps track of things like this. So, even though you may get G68.2 output that will rotate to the correct orientation on your machine, your XY code may be "skewed" and not match your Tilted Work Plane orientation, because you haven't matched the rotary and linear mapping calculations.

Looks like I spoke too soon. Taking this down.

Index the geometry (rotate) from the Top. Is the slot essentially "4-Axis" wrapped around a cylinder, or do you need full 5-Axis motion to cut the slot?

Look in your Windows Start Menu > scroll down to the "Mastercam" folder, and find the "Quick Reference Card". Lots of shortcuts and handy tips there! In the "Data Entry Field", instead of typing a letter, Right-Click, and you'll get the full shortcut list. Also, are you aware you can do "math" in any field with a yellow background? This is a "calculatable value field", and you can not only do simple math, but can use parenthesis as well, to form more complex calculations. For example > (0.8775/2) * 1.414

Change-at-Point is the best solution, because those changes are attached to the "chain", so the changes can be made in the Chaining Manager, and the modifications "stick" through regeneration.