4th axis problem

[domino]

I am just making my first four axis part and have discovered a problem. I think it is coming from my post processor editor, but I am not sure. Here is what is happening physically: the tool feeds to the clearance plane and the a axis turns on, but then the a axis just spins and the tool does not feed past it just hangs there.

The machining operation I have programmed is a 4th axis roughing op, set up as an across axis zig movement (pseudo lathe turning). G code is as follows:

O001
N10 M25 G49
N12 G17 G40
N14 G21
N16 G80
N18 G90
N20 G98
N22 ;4th Axis Roughing
N24 G0 Z4.
N26 G0 X17. Y0.
N28 T11 M06
N30 S6000 M3
N32 G1 X-85. Y0. F1829.
N34 G43 Z21.5 H11
N36 A0.F1829.
N38 Z17.5A0.
N40 Z21.5A-360.F3657.
N42 X-80.238A-360.
N44 Z17.5A-360.F1829.
N46 Z21.5A-720.F3657.
N48 X-75.475A-720.
N50 Z17.5A-720.F1829.
N52 Z21.5A-1080.F3657.
N54 X-70.713A-1080.
N56 Z17.5A-1080.F1829.
N58 Z21.5A-1440.F3657.
N60 X-65.95A-1440.
etc..
The program hangs up at N36.

I am using the Ajax Centroid post with the default 4th axis motion commands.

[MecSoft Support]

The posted code does not show any errors. Your controller is probably expecting a coordinate motion along with the rotation axis code. The coordinate output in the post is set to Modal by default in your post processor.
Line N36 only shows the rotation axis code as the X Y and Z values have not changed from Line N32 and N34.
You can set the coordinate output to Non Modal in the post processor and see if this helps.
Go to Setup tab in VisualMILL -MOps browser and select Set Post Options. Click edit and under General tab, clear the check box for Coordinate located under Modal Output.
Save and close the post processor.
Post process your toolpath.