[post_guy]

The default MPFAN in V9 contained some limited logic for this. To do it properly, open the .pst file and find the following section:

pxyzcout        #Map coordinates
      if rot_on_x,
        [
        if cuttype = zero, pxyzcout0    #Toolplane Positioning
        if cuttype = one, pxyzcout1     #Axis Substitution
        if cuttype = two, pxyzcout2     #Polar Conversion
        if cuttype = three, pxyzcout3   #Simulatneous 4 axis (Multi-axis)
        if rot_ccw_pos = one, csav = -csav
        if mr_rt_actv <> two,
          [
          pcoutrev
          if index, pindxcalc
          pfcalc
          ]
        else, feed = fr_pos  
        ]
      else,
        [
        xabs = vequ (x)               
        feed = fr_pos
        ]  
        
      #Check flags and change orientation         # - eap 1/17/03        
      if xflip = yes, xabs = xabs * -1            # - eap 1/17/03
      if yflip = yes, yabs = yabs * -1            # - eap 1/17/03        
      if zflip = yes, zabs = zabs * -1            # - eap 1/17/03

The xflip and yflip and zflip variables are the ones you are really interested in. The logic needs to be modified to work properly. Change it to:

      #Check flags and change orientation         # - eap 1/17/03        
      if xflip = yes,
        [
        xabs = xabs * -1
        i = i * -1
        ]
      if yflip = yes,
        [
        yabs = yabs * -1
        j = j * -1
        ]
      if zflip = yes,
        [
        zabs = zabs * -1
        k = k * -1
        ]

Now find the variable initializations in the post:

xflip       : no    #Reverse X axis orientation                - eap 1/17/03
yflip       : no    #Reverse Y axis orientation                - eap 1/17/03
zflip       : no    #Reverse Z axis orientation                - eap 1/17/03

and change them to:

xflip       : yes   #Reverse X axis orientation                - eap 1/17/03
yflip       : yes   #Reverse Y axis orientation                - eap 1/17/03
zflip       : no    #Reverse Z axis orientation                - eap 1/17/03