The details are all laid out here:

http://forum.planet-cnc.com/viewtopic.php?f=5&t=1846

This is the test program:

Code:
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G18               ( Force XZ Plane )
G21               ( Force Metric Dimensioning )
G40               ( Force Tool Nose Compensation To OFF )
G80               ( Cancel Any Modal Motion )
G90               ( Force Absolute Coordinate Positioning )

G53 G00 X60 Z100      ( Move Turret To Safe Position For Tool Change )
G04 P10            ( Pause For 10 Seconds To Allow Notation Of Axis Locations )

G91               ( Force Relative Coordinate Positioning To Stop Turret Reversing To Location )
G00 A16            ( Rotate To Tool Position 3 )
G01 A-2 F100         ( Rotate Back Against Pawl At Feed 100 )
G90               ( Force Absolute Coordinate Positioning For Machining Passes )      
T3               ( Force Tool Change For Tool 3 )
M6               ( Force Use Of New Tool )
G43 H3            ( Force Use Of Tool 3 Offsets )

G00 X30 Z60         ( Simulate Program Moves )
G04 P10            ( Pause For 10 Seconds To Allow Notation Of Axis Locations )

G53 G00 X60 Z100      ( Move Turret To Safe Position For Tool Change )
G04 P10            ( Pause For 10 Seconds To Allow Notation Of Axis Locations )

G91               ( Force Relative Coordinate Positioning To Stop Turret Reversing To Location )
G00 A46            ( Rotate To Tool Position 1 )
G01 A-2 F100         ( Rotate Back Against Pawl At Feed 100 )
G90               ( Force Absolute Coordinate Positioning For Future Machining Passes )      
T1               ( Force Tool Change For Tool 1 )
M6               ( Force Use Of New Tool )
G43 H1            ( Force Use Of Tool 1 Offsets )

M2               ( End Program )
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I start the machine off with no offsets on any tools. Tool Offset is set to "Not Used" in the Tool Change settings page. Before every pass, the tool is homed using the limit switches, which leaves it at X65, Z105.

What I'm seeing is that the final absolute position at the end of the program is the "G53 G00 X60 Z100" commanded position, but minus the Tool 3 X offset value. That in itself is odd, but it's also affecting both the X and Z axes, by the same amount. In other words, the final Z position is minus the T3 X offset, not the T3 Z offset:

To get a safe automated tool change, I need to be able to get the carriage to a known safe location, and at the moment I can't do that. Changing from G90 to G91 also seems to have the side effect that the next movement control, on any axis, caused motion on all axes. This usually results in the machine going out of limits, but has also caused a couple of turret/chuck interfaces.

Adrian.