ngcgui subroutine tool tip diameter

I am playing with ngcgui and specifically the face.ngc routine. It says in the comments in that subroutine that "variable 5410 is the current tool tip diameter...". I had my tool tip diameter set to 0.1 for all my tools just so it would display a triangle for the tool in Axis. But in using the face.ngc routine the tool was going well below X0 (0.3") which broke the (brittle) carbide tipped tool when it was brushing the backside of the tool below zero. I changed the tool tip in the tool table after I read this comment to 0.032" (I have a CCMT32.51 insert which claims to be 0.016" radius tip) and it looks like it gets closer to X0 but is still quite a bit below it. I looked in the subroutine and see that even though G43 (cutter compensation) is turned on that the X travel is adjusted even further down with the line "G1 X-[#5410*3]". This explains a) why my tool when to 0.3" below X, and b) why it is still going below X at 0.032" diameter (3x0.032 is nearly 0.1").

Why would you want to go past the center of your part by 3 times the diameter of the tool tip? That seems very excessive.

Doesn't cutter comp (G43) get the tip all the way down to zero? If not, then I see that you might want to go down to where the edge of the radius touches zero BUT that is probably less than 1 X the radius of the tip...

-Tom

my thoughts are it should be that the variable 5410 should be radius rather than diameter .
may be wrong but could be a typo .

andypugh wrote:

I generally face to -1mm. I don't actually see how that can cause a problem unless centre height is rather a long way off.

If your tool is below the center it isn't cutting anymore because the workpiece is spinning against the non-cutting surface of the tool. In my case this caused the carbide insert to chip on its edge.

andypugh wrote:

Cutter radius compensation on a lathe won't compensate in X when facing. It only affects "slanted" cuts where the radius tends to leave excess material.

I see, yes.
Thanks,
-Tom