[blakemachine]

Ok, so I have this block, and in the block is a through hole off center. I am drilling and boring from each end with rotating 180deg for indexing. I set WCS at top. C and T planes are at bottom for the indexing tool path. I then look at the post with 4th axis and rotary axis positioning about x axis turned on. This is what it does.

G20
N102 G0 G17 G40 G49 G80 G90
N104 T4 M6
N106 G0 G90 G54 X-.0115 Y.0861 A0. S1800 M3
N108 G43 H4 Z6.
N110 Z3.63
N112 G1 Z-.065 F2.
N114 X.0115 F5.
N116 G3 X.664 Y.75 R.664
N118 G1 X-.664
N120 G2 X-.0115 Y1.4139 R.664
N122 G1 X.0115
N124 Z.035 F25.
N126 G0 Z.25
N128 Z3.63
N130 A180.
N132 X-.674 Y.75
N134 G1 Z-.065 F2.
N136 G3 X.674 R.674 F5.
N138 X-.674 R.674
N140 G1 Z.035 F25.
N142 G0 Z6.
N144 M5
N146 G91 G28 Z0.
N148 G28 X0. Y0. A0.
N150 M30


Can someone advise why its doing a 180 in the middle of the program?

[Superman]

The A180. is the NC rotary command to move the 4th axis to enable machining the hole from the opposite side. You did also notice the A0. on line N106 ?

Query ????
Did you use the system BOTTOM view ??
This IS NOT a correct view that a vertical machine ( with the 4 axis around X) is capable of. You will find that the NC code is 180° ( around Z ) out of position.
You have to avoid using the BACK & BOTTOM ( system views ) & create the correct ones yourself.

PS
You have sometimg strange going on, the top contour is doing a R0.664, but on the bottom, it is R0.674--- you have either different XY offset values, or the contours you have selected are different rads.......then again it may be intentional